LHC+ Ingredients & Drug Interactions

Green tea extract seems to reduce the levels and clinical effects of atorvastatin.
In healthy humans, taking green tea extract 300 mg or 600 mg along with atorvastatin reduces plasma levels of atorvastatin by approximately 24%. The elimination of atorvastatin is not affected. Atorvastatin is a substrate of organic anion-transporting polypeptides (OATPs). Research shows that two of the major catechins found in green tea, epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), inhibit OATPs. Some OATPs are expressed in the small intestine and are responsible for the uptake of drugs and other compounds, which may have resulted in reduced plasma levels of atorvastatin. It is not clear if drinking green tea alters the absorption of atorvastatin.

Theoretically, concomitant use might increase the risk for stimulant adverse effects.
Green tea contains caffeine. There is evidence that using ephedrine with caffeine might increase the risk of serious life-threatening or debilitating adverse effects such as hypertension, myocardial infarction, stroke, seizures, and death.

Green tea seems to reduce the levels and clinical effects of nadolol.
Preliminary clinical research shows that green tea consumption reduces plasma concentrations of nadolol. Compared to a control group, both peak levels and total drug exposure (AUC) of nadolol were reduced by approximately 85% in subjects who drank green tea daily for two weeks. Drinking green tea with nadolol also significantly reduced nadolol's systolic blood pressure lowering effect. Other clinical research shows that a single dose of green tea can affect plasma nadolol levels for at least one hour. Green tea catechins have been shown to inhibit organic anion transporting polypeptides (OATP), one of which, OATP1A2, is involved in the uptake of nadolol in the intestine The interaction is thought to be due primarily to the epigallocatechin gallate (EGCG) content of green tea.

Theoretically, high doses of green tea might increase the effects and side effects of 5-fluorouracil.
Animal research shows that taking green tea in amounts equivalent to about 6 cups daily in humans for 4 weeks prior to receiving a single injection of 5-fluorouracil increases the maximum plasma levels of 5-fluorouracil by about 2.5-fold and the area under the curve by 425%.

Theoretically, green tea might decrease the vasodilatory effects of adenosine and interfere with its use prior to stress testing.
Green tea contains caffeine. Caffeine is a competitive inhibitor of adenosine at the cellular level. However, caffeine doesn't seem to affect supplemental adenosine because high interstitial levels of adenosine overcome the antagonistic effects of caffeine. It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests. However, methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing.

Theoretically, green tea may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Conflicting reports exist regarding the effect of green tea on bleeding risk when used with anticoagulant or antiplatelet drugs; however, most evidence suggests that drinking green tea in moderate amounts is unlikely to cause a significant interaction. Green tea contains small amounts of vitamin K, approximately 7 mcg per cup. Some case reports have associated the antagonism of warfarin with the vitamin K content of green tea. However, these reports are rare, and very large doses of green tea (about 8-16 cups daily) appear to be needed to cause these effects. Furthermore, the catechins and caffeine in green tea are reported to have antiplatelet activity.

Green tea contains caffeine. Theoretically, concomitant use of large amounts of caffeine might increase cardiac inotropic effects of beta-agonists.

Theoretically, green tea might interfere with the effects of bortezomib.
In vitro research shows that green tea polyphenols, such as epigallocatechin gallate (EGCG), interact with bortezomib and block its proteasome inhibitory action. This prevents the induction of cell death in multiple myeloma or glioblastoma cancer cell lines. Advise patients taking bortezomib, not to take green tea.

Theoretically, green tea might reduce the effects of carbamazepine and increase the risk for convulsions.
Green tea contains caffeine. Animal research suggests that taking caffeine can lower the anticonvulsant effects of carbamazepine and can induce seizures when taken in doses above 400 mg/kg. Human research has shown that taking caffeine 300 mg in three divided doses along with carbamazepine 200 mg reduces the bioavailability of carbamazepine by 32% and prolongs the plasma half-life of carbamazepine 2-fold in healthy individuals.

Theoretically, green tea might reduce the levels and clinical effects of celiprolol.
In a small human study, taking green tea daily for 4 days appears to decrease blood and urine levels of celiprolol by at least 98%. This interaction is possibly due to the inhibition of organic anion transporting polypeptide (OATP). Green tea catechins have been shown to inhibit organic anion transporting polypeptides (OATP), one of which, OATP1A2, is found in the intestine The interaction is thought to be due primarily to the epigallocatechin gallate (EGCG) content of green tea.

Theoretically, concomitant use might increase the effects and adverse effects of caffeine in green tea.
Green tea contains caffeine. Cimetidine can reduce caffeine clearance by 31% to 42%.

Theoretically, green tea might increase the levels and adverse effects of clozapine and acutely exacerbate psychotic symptoms.
Animal research suggests that, although green tea extract does not affect the elimination of clozapine, it delays the time to reach peak concentration and reduces the peak plasma levels. Also, concomitant administration of green tea and clozapine might theoretically cause acute exacerbation of psychotic symptoms due to the caffeine in green tea. Caffeine can increase the effects and toxicity of clozapine. Caffeine doses of 400-1000 mg daily inhibit clozapine metabolism. Clozapine is metabolized by cytochrome P450 1A2 (CYP1A2). Researchers speculate that caffeine might inhibit CYP1A2. However, there is no reliable evidence that caffeine affects CYP1A2. There is also speculation that genetic factors might make some patients be more sensitive to the interaction between clozapine and caffeine.

Theoretically, concomitant use might increase the effects and adverse effects of caffeine found in green tea.
Green tea contains caffeine. Oral contraceptives can decrease caffeine clearance by 40% to 65%.

Theoretically, concomitant use might increase the levels and adverse effects of caffeine.
Green tea contains caffeine. Caffeine is metabolized by cytochrome P450 1A2 (CYP1A2),. Theoretically, drugs that inhibit CYP1A2 may decrease the clearance rate of caffeine from green tea and increase caffeine levels.

Theoretically, green tea might decrease the vasodilatory effects of dipyridamole and interfere with its use prior to stress testing.
Green tea contains caffeine. Caffeine might inhibit dipyridamole-induced vasodilation. It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests. Methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing.

Theoretically, disulfiram might increase the risk of adverse effects from caffeine.
In human research, disulfiram decreases the clearance and increases the half-life of caffeine.

Theoretically, using green tea with diuretic drugs might increase the risk of hypokalemia.
Green tea contains caffeine. In excessive amounts, caffeine can reduce potassium levels due to stimulation of the sodium-potassium pump. Diuretics can also cause lower potassium levels.

Theoretically, estrogens might increase the levels and adverse effects of caffeine.
Green tea contains caffeine. Estrogen inhibits caffeine metabolism.

Theoretically, green tea might reduce the effects of ethosuximide and increase the risk for convulsions.
Green tea contains caffeine. Animal research suggests that caffeine 92.4 mg/kg can decrease the anticonvulsant activity of ethosuximide. However, this effect has not been reported in humans.

Theoretically, green tea might reduce the effects of felbamate and increase the risk for convulsions.
Green tea contains caffeine. Animal research suggests that a high dose of caffeine 161.7 mg/kg can decreases the anticonvulsant activity of felbamate. However, this effect has not been reported in humans.

Green tea can decrease blood levels of fexofenadine.
Clinical research shows that green tea can significantly decrease blood levels and excretion of fexofenadine. Taking green tea extract with a dose of fexofenadine decreased bioavailability of fexofenadine by about 30%. In vitro, green tea inhibits the cellular accumulation of fexofenadine by inhibiting the organic anion transporting polypeptide (OATP) drug transporter. Research shows that two of the major catechins found in green tea, epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), inhibit OATPs, specifically OATP1A2, OATP1B1, and OATP2B1. In addition, green tea has been shown to reduce the absorption of some drugs that are OATP substrates.

Theoretically, green tea might increase the levels and adverse effects of flutamide.
Green tea contains caffeine. In vitro evidence suggests that caffeine can inhibit the metabolism of flutamide. Theoretically, concomitant use of caffeine and flutamide might increase serum concentrations of flutamide and increase the risk adverse effects.

Theoretically, fluvoxamine might increase the levels and adverse effects of caffeine.
Green tea contains caffeine. Fluvoxamine reduces caffeine metabolism.

Theoretically, concomitant use might have additive adverse hepatotoxic effects.
Green tea extract supplements have been linked to several cases of hepatotoxicity and might have additive hepatotoxic effects with other drugs..

Theoretically, green tea might reduce the levels and clinical effects of imatinib.
In animal research, a single dose of green tea extract reduces the area under the curve (AUC) of imatinib by up to approximately 64% and its main metabolite N-desmethyl imatinib by up to approximately 81%. This interaction has not been shown in humans. The mechanism of action is unclear but may involve multiple pathways.

Taking ginkgo with talinolol seems to increase blood levels of talinolol.
There is some evidence that using ginkgo leaf extract 120 mg orally three times daily for 14 days can increase levels of talinolol by 36% in healthy male individuals. However, single doses of ginkgo do not seem to affect talinolol pharmacokinetics.

Theoretically, ginkgo might decrease the levels and clinical effects of alprazolam.
In clinical research, ginkgo extract (Ginkgold) 120 mg twice daily seems to decrease alprazolam levels by about 17%. However, ginkgo does not appear to decrease the elimination half-life of alprazolam. This suggests that ginkgo is more likely to decrease absorption of alprazolam rather than induce hepatic metabolism of alprazolam.

Ginkgo has been shown to increase the risk of bleeding in some people when taken with warfarin. Theoretically, ginkgo might increase the risk of bleeding if used with other anticoagulant or antiplatelet drugs.
Several pharmacodynamic studies suggest that ginkgo inhibits platelet aggregation. It is thought that the ginkgo constituent, ginkgolide B, displaces platelet-activating factor (PAF) from its binding sites, decreasing blood coagulation. Several case reports have documented serious bleeding events in patients taking ginkgo. However, population and clinical studies have produced mixed results. Some evidence shows that short-term use of ginkgo leaf does not significantly reduce platelet aggregation and blood clotting. A study in healthy males who took a specific ginkgo leaf extract (EGb 761) 160 mg twice daily for 7 days found no change in prothrombin time. An analysis of a large medical record database suggests that ginkgo increases the risk of a bleeding adverse event by 38% when taken concurrently with warfarin. It has been suggested that ginkgo has to be taken for at least 2-3 weeks to have a significant effect on platelet aggregation. However, a meta-analysis of 18 studies using standardized ginkgo extracts, 80-480 mg daily for up to 32 weeks, did not find a significant effect on platelet aggregation, fibrinogen concentration, or PT/aPTT. In addition, a single dose of ginkgo plus clopidogrel or ticlopidine does not seem to significantly increase bleeding time or platelet aggregation. Also, taking ginkgo leaf extract daily for 8 days in conjunction with rivaroxaban does not affect anti-factor Xa activity; however, this study did not evaluate bleeding time.

Theoretically, ginkgo might reduce the effectiveness of anticonvulsants.
Ginkgo seeds contain ginkgotoxin. Large amounts of ginkgotoxin can cause neurotoxicity and seizure. Ginkgotoxin is present in much larger amounts in ginkgo seeds than leaves. Ginkgo leaf extract contains trace amounts of ginkgotoxin. The amount of ginkgotoxin in ginkgo leaf and leaf extract seems unlikely to cause toxicity. However, there are anecdotal reports of seizure occurring after use of ginkgo leaf both in patients without a history of seizure disorder and in those with previously well-controlled epilepsy.

Theoretically, taking ginkgo with antidiabetes drugs might alter the response to antidiabetes drugs.
Ginkgo leaf extract seems to alter insulin secretion and metabolism, and might affect blood glucose levels in people with type 2 diabetes. The effect of ginkgo seems to differ depending on the insulin and treatment status of the patient. In diet-controlled diabetes patients with hyperinsulinemia, taking ginkgo does not seem to significantly affect insulin or blood glucose levels. In patients with hyperinsulinemia who are treated with oral hypoglycemic agents, taking ginkgo seems to decrease insulin levels and increase blood glucose following an oral glucose tolerance test. Researchers speculate that this could be due to ginkgo-enhanced hepatic metabolism of insulin. In patients with pancreatic exhaustion, taking ginkgo seems to stimulate pancreatic beta-cells, resulting in increased insulin and C-peptide levels, but with no significant change in blood glucose levels in response to an oral glucose tolerance test.

Theoretically, ginkgo might decrease the levels and clinical effects of atorvastatin.
In humans, intake of ginkgo extract appears to increase atorvastatin clearance, reducing the area under the curve of atorvastatin by 10% to 14% and the maximum concentration by 29%. However, this interaction does not appear to affect cholesterol synthesis and absorption. Further, a model in rats with hyperlipidemia suggests that administering ginkgo extract does not impact blood levels of atorvastatin and leads to lower total cholesterol, low-density lipoprotein cholesterol, and triglycerides when compared with rats given atorvastatin alone.

Theoretically, ginkgo might increase levels of drugs metabolized by CYP1A2.
Laboratory research suggests that ginkgo leaf extract can mildly inhibit CYP1A2 enzymes. However, clinical research suggests ginkgo might not affect CYP1A2. Until more is known, use ginkgo cautiously in patients taking drugs metabolized by these enzymes.

Theoretically, ginkgo might decrease levels of drugs metabolized by CYP2C19.
Some clinical research shows that a specific ginkgo leaf extract (Remembrance, Herbs Product LTD) 140 mg twice daily can induce CYP2C19 enzymes and potentially decrease levels of drugs metabolized by these enzymes. However, other clinical research shows that taking ginkgo 120 mg twice daily for 12 days has no effect on levels of drugs metabolized by CYP2C19.

Theoretically, ginkgo might increase levels of drugs metabolized by CYP2C9.
In vitro, a specific standardized extract of ginkgo leaf (EGb 761) inhibits CYP2C9 activity . The terpenoid (ginkgolides) and flavonoid (quercetin, kaempferol, etc.) constituents seem to be responsible for this effect. Most ginkgo extracts contain some amount of these constituents. Therefore, other ginkgo leaf extracts might also inhibit the CYP2C9 enzyme. However, clinical research suggests that ginkgo might not have a significant effect on CYP2C9 in humans. Ginkgo does not seem to significantly affect the pharmacokinetics of CYP2C9 substrates diclofenac or tolbutamide.

Theoretically, ginkgo might decrease levels of drugs metabolized by CYP3A4.
There is conflicting evidence about whether ginkgo induces or inhibits CYP3A4. Ginkgo does not appear to affect hepatic CYP3A4. However, it is not known if ginkgo affects intestinal CYP3A4. Preliminary clinical research suggests that taking ginkgo does not significantly affect levels of donepezil, lopinavir, or ritonavir, which are all CYP3A4 substrates. Other clinical research also suggests ginkgo does not significantly affect CYP3A4 activity. However, there are two case reports of decreased efavirenz concentrations and increased viral load in patients taking ginkgo. It is suspected that terpenoids from the ginkgo extract reduced drug levels by inducing cytochrome P450 3A4 (CYP3A4).

Theoretically, ginkgo might decrease the levels and clinical effects of efavirenz.
There are two case reports of decreased efavirenz concentrations and increased viral load in patients taking ginkgo. In one case, an HIV-positive male experienced over a 50% decrease in efavirenz levels over the course of 14 months while taking ginkgo extract. HIV-1 RNA copies also increased substantially, from less than 50 to more than 1500. It is suspected that terpenoids from the ginkgo extract reduced drug levels by inducing cytochrome P450 3A4 (CYP3A4). In another case report, a patient stable on antiviral therapy including efavirenz for 10 years, had an increase in viral load from <50 copies/mL to 1350 copies/mL after 2 months of taking a combination of supplements including ginkgo. After stopping ginkgo, the viral load was again controlled with the same antiviral therapy regimen.

Theoretically, ginkgo might increase the risk of bleeding when used with ibuprofen.
Ginkgo might have antiplatelet effects and has been associated with several case reports of spontaneous bleeding. In one case, a 71-year-old male had taken a specific ginkgo extract (Gingium, Biocur) 40 mg twice daily for 2.5 years. About 4 weeks after starting ibuprofen 600 mg daily he experienced a fatal intracerebral hemorrhage. However, the antiplatelet effects of ginkgo have been questioned. A meta-analysis and other studies have not found a significant antiplatelet effect with standardized ginkgo extracts, 80 mg to 480 mg taken daily for up to 32 weeks.

Theoretically, taking ginkgo with P-glycoprotein substrates might increase the levels and adverse effects of these substrates.
A small clinical study in healthy volunteers shows that using ginkgo leaf extract 120 mg orally three times daily for 14 days can increase levels of the P-glycoprotein substrate, talinolol, by 36% in healthy male individuals. However, single doses of ginkgo do not have the same effect.

Theoretically, taking ginkgo with risperidone might increase the levels and adverse effects of risperidone.
A single case of priapism has been reported for a 26-year-old male with schizophrenia who used risperidone 3 mg daily along with ginkgo extract 160 mg daily. Risperidone is metabolized by cytochrome P450 (CYP) 2D6 and CYP3A4. CYP3A4 activity might be affected by ginkgo. Theoretically, ginkgo may inhibit the metabolism of risperidone and increase the risk of adverse effects.

Theoretically, ginkgo might decrease the levels and clinical effects of rosiglitazone.
Animal research shows that ginkgo leaf extract orally 100 or 200 mg/kg daily for 10 days alters the pharmacodynamics of rosiglitazone in a dose-dependent manner. The 100 mg/kg and 200 mg/kg doses reduce the area under the concentration time curve (AUC) of rosiglitazone by 39% and 52%, respectively, and the half-life by 28% and 39%, respectively. It is hypothesized that these changes may be due to induction of cytochrome P450 2C8 by ginkgo.

Theoretically, taking ginkgo with drugs that lower the seizure threshold might increase the risk for convulsions.
Ginkgo seeds contain ginkgotoxin. Large amounts of ginkgotoxin can cause neurotoxicity and seizure. Ginkgotoxin is present in much larger amounts in ginkgo seeds than leaves. Ginkgo leaf extract contains trace amounts of ginkgotoxin. The amount of ginkgotoxin in ginkgo leaf and leaf extract seems unlikely to cause toxicity. However, there are anecdotal reports of seizure occurring after use of ginkgo leaf both in patients without a history of seizure disorder and in those with previously well-controlled epilepsy.

Theoretically, ginkgo might decrease the levels and clinical effects of simvastatin.
Clinical research shows that taking ginkgo extract can reduce the area under the curve and maximum concentration of simvastatin by 32% to 39%. However, ginkgo extract does not seem to affect the cholesterol-lowering ability of simvastatin.

Theoretically, ginkgo might increase the levels and clinical effects of sofosbuvir.
Animal research in rats shows that giving a ginkgo extract 25 mg/kg orally daily for 14 days increases the area under the concentration time curve (AUC) after a single sofosbuvir dose of 40 mg/kg by 11%, increases the half-life by 60%, and increases the plasma concentration at 4 hours by 38%. This interaction appears to be related to the inhibition of intestinal P-glycoprotein by ginkgo.

Theoretically, ginkgo might increase the blood levels of tacrolimus.
In vitro evidence suggests that certain biflavonoids in ginkgo leaves (i.e. amentoflavone, ginkgetin, bilobetin) may inhibit the metabolism of tacrolimus by up to 50%. This interaction appears to be time-dependent and due to inhibition of cytochrome P450 (CYP) 3A4 by these bioflavonoids. In rats given tacrolimus 1 mg/kg orally, amentoflavone was shown to increase the area under the concentration time curve (AUC) of tacrolimus by 3.8-fold.

Theoretically, ginkgo might increase the levels and clinical effects of trazodone.
In a case report, an Alzheimer patient taking trazodone 20 mg twice daily and ginkgo leaf extract 80 mg twice daily for four doses became comatose. The coma was reversed by administration of flumazenil (Romazicon). Coma might have been induced by excessive GABA-ergic activity. Ginkgo flavonoids are thought to have GABA-ergic activity and act directly on benzodiazepine receptors. Ginkgo might also increase metabolism of trazodone to active GABA-ergic metabolites, possibly by inducing cytochrome P450 3A4 (CYP3A4) metabolism.

Ginkgo has been shown to increase the risk of bleeding in some people when taken with warfarin.
Several pharmacodynamic studies suggest that ginkgo inhibits platelet aggregation. It is thought that the ginkgo constituent, ginkgolide B, displaces platelet-activating factor (PAF) from its binding sites, decreasing blood coagulation. Several case reports have documented serious bleeding events in patients taking ginkgo. Information from a medical database suggests that when taken concurrently with warfarin, ginkgo increases the risk of a bleeding adverse event by 38%. There is also some evidence that ginkgo leaf extract can inhibit cytochrome P450 2C9, an enzyme that metabolizes warfarin. This could result in increased warfarin levels. However, population and clinical research has produced mixed results. Clinical research in healthy people suggests that ginkgo has no effect on INR, or the pharmacokinetics or pharmacodynamics of warfarin. A meta-analysis of 18 studies using standardized ginkgo extracts, 80 mg to 480 mg daily for up to 32 weeks, did not find a significant effect on platelet aggregation, fibrinogen concentration, or PT/aPTT. There is also some preliminary clinical research that suggests ginkgo might not significantly increase the effects of warfarin in patients that have a stable INR.

Theoretically, taking ginkgo with oral, but not intravenous, nifedipine might increase levels and adverse effects of nifedipine.
Animal research and some clinical evidence suggests that taking ginkgo leaf extract orally in combination with oral nifedipine might increase nifedipine levels and cause increased side effects, such as headaches, dizziness, and hot flushes. However, taking ginkgo orally does not seem to affect the pharmacokinetics of intravenous nifedipine.

Theoretically, taking ginkgo with omeprazole might decrease the levels and clinical effects of omeprazole.
Clinical research shows that a specific ginkgo leaf extract (Remembrance, Herbs Product LTD) 140 mg twice daily can induce cytochrome P450 (CYP) 2C19 enzymes and decrease levels of omeprazole by about 27% to 42%.

Turmeric has antioxidant effects. Theoretically, this may reduce the activity of chemotherapy drugs that generate free radicals. However, research is conflicting.
In vitro research suggests that curcumin, a constituent of turmeric, inhibits mechlorethamine-induced apoptosis of breast cancer cells by up to 70%. Also, animal research shows that curcumin inhibits cyclophosphamide-induced tumor regression. However, some in vitro research shows that curcumin does not affect the apoptosis capacity of etoposide. Also, other laboratory research suggests that curcumin might augment the cytotoxic effects of alkylating agents. Reasons for the discrepancies may relate to the dose of curcumin and the specific chemotherapeutic agent. Lower doses of curcumin might have antioxidant effects while higher doses might have pro-oxidant effects. More evidence is needed to determine what effect, if any, turmeric might have on alkylating agents.

Taking turmeric with amlodipine may increase levels of amlodipine.
Animal research shows that giving amlodipine 1 mg/kg as a single dose following the use of turmeric extract 200 mg/kg daily for 2 weeks increases the maximum concentration and area under the curve by 53% and 56%, respectively, when compared with amlodipine alone. Additional animal research shows that taking amlodipine 1 mg/kg with a curcumin 2 mg/kg pretreatment for 10 days increases the maximum concentration and area under the curve by about 2-fold when compared with amlodipine alone.

Turmeric may have antiplatelet effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs. However, research is conflicting.
Curcumin, a constituent of turmeric, has demonstrated antiplatelet effects in vitro. Furthermore, two case reports have found that taking turmeric along with warfarin or fluindione was associated with an increased international normalized ratio (INR). However, one clinical study in healthy volunteers shows that taking curcumin 500 mg daily for 3 weeks, alone or with aspirin 100 mg, does not increase antiplatelet effects or bleeding risk. It is possible that the dose of turmeric used in this study was too low to produce a notable effect.

Theoretically, taking turmeric with antidiabetes drugs might increase the risk of hypoglycemia.
Animal research and case reports suggest that curcumin, a turmeric constituent, can reduce blood glucose levels in patients with diabetes. Furthermore, clinical research in adults with type 2 diabetes shows that taking curcumin 475 mg daily for 10 days prior to taking glyburide 5 mg decreased postprandial glucose levels for up to 24 hours when compared with glyburide alone, despite the lack of a significant pharmacokinetic interaction. Other clinical studies in patients with diabetes show that taking curcumin daily can reduce blood glucose levels when compared with placebo.

Turmeric has antioxidant effects. Theoretically, this may reduce the activity of chemotherapy drugs that generate free radicals. However, research is conflicting.
In vitro and animal research shows that curcumin, a constituent of turmeric, inhibits doxorubicin-induced apoptosis of breast cancer cells by up to 65%. However, curcumin does not seem to affect the apoptosis capacity of daunorubicin. In fact, some research shows that curcumin might augment the cytotoxic effects of antitumor antibiotics, increasing their effectiveness. Reasons for the discrepancies may relate to the dose of curcumin and the chemotherapeutic agent. Lower doses of curcumin might have antioxidant effects while higher doses might have pro-oxidant effects. More evidence is needed to determine what effects, if any, antioxidants such as turmeric have on antitumor antibiotics.

Turmeric might increase or decrease levels of drugs metabolized by CYP3A4.
In vitro and animal research show that turmeric and its constituents curcumin and curcuminoids inhibit CYP3A4. Also, 8 case reports from the World Health Organization (WHO) adverse drug reaction database describe increased toxicity in patients taking turmeric and cancer medications that are CYP3A4 substrates, including everolimus, ruxolitinib, ibrutinib, and palbociclib, and bortezomib. In another case report, a transplant patient presented with acute nephrotoxicity and elevated tacrolimus levels after consuming turmeric powder at a dose of 15 or more spoonfuls daily for ten days prior. It was thought that turmeric increased levels of tacrolimus due to CYP3A4 inhibition.
Conversely, other in vitro research suggests that turmeric induces CYP3A4 activity, leading to reduced levels of CYP3A4 substrates. An animal model suggests that induction of CYP3A4 occurs after daily curcumin use for 1 week. However, the induction of CYP3A4 by turmeric has not been reported in humans.

Theoretically, turmeric might increase the risk of liver damage when taken with hepatotoxic drugs.
There is concern that turmeric might cause hepatotoxicity, especially when highly bioavailable formulations are used in high doses.

Theoretically, turmeric might have additive effects when used with hepatotoxic drugs such as methotrexate.
In one case report, a 39-year-old female taking methotrexate, turmeric, and linseed oil developed hepatotoxicity.

Theoretically, turmeric might increase blood levels of OATP4C1 substrates.
In vitro research shows that the turmeric constituent curcumin competitively inhibits OATP4C1 transport. This transporter is expressed in the kidney and facilitates the renal excretion of certain drugs. Theoretically, taking turmeric might decrease renal excretion of OATP substrates.

Turmeric might increase the effects and adverse effects of sulfasalazine.
Clinical research shows that taking the turmeric constituent, curcumin, can increase blood levels of sulfasalazine by 3.2-fold.

Turmeric might increase the effects and adverse effects of tacrolimus.
In one case report, a transplant patient presented with acute nephrotoxicity and elevated tacrolimus levels of 29 ng/mL. The patient previously had tacrolimus levels within the therapeutic range at 9.7 ng/mL. Ten days prior to presenting at the emergency room the patient started consumption of turmeric powder at a dose of 15 or more spoonfuls daily. It was thought that turmeric increased levels of tacrolimus due to cytochrome P450 3A4 (CYP3A4) inhibition. In vitro and animal research show that turmeric and its constituent curcumin inhibit CYP3A4.

Turmeric may reduce the absorption of talinolol in some situations.
Clinical research shows that taking curcumin for 6 days decreases the bioavailability of talinolol when taken together on the seventh day. The clinical significance of this effect is unclear.

Theoretically, turmeric might reduce the levels and clinical effects of tamoxifen.
In a small clinical trial in patients with breast cancer taking tamoxifen 20-30 mg daily, adding curcumin 1200 mg plus piperine 10 mg three times daily reduces the 24-hour area under the curve of tamoxifen and the active metabolite endoxifen by 12.8% and 12.4%, respectively, as well as the maximum concentrations of tamoxifen, when compared with tamoxifen alone. However, in the absence of piperine, the area under the curve for endoxifen and the maximum concentration of tamoxifen were not significantly reduced. Effects were most pronounced in patients who were extensive cytochrome P450 (CYP) 2D6 metabolizers.

Turmeric has antioxidant effects. There is some concern that this may reduce the activity of chemotherapy drugs that generate free radicals. However, research is conflicting.
In vitro research shows that curcumin, a constituent of turmeric, inhibits camptothecin-induced apoptosis of breast cancer cells by up to 71%. However, other in vitro research shows that curcumin augments the cytotoxic effects of camptothecin. Reasons for the discrepancies may relate to the dose of curcumin and the chemotherapeutic agents. Lower doses of curcumin might have antioxidant effects while higher doses might have pro-oxidant effects. More evidence is needed to determine what effect, if any, turmeric might have.

Theoretically, turmeric might increase or decrease levels of tramadol.
Animal research suggests that a single dose of curcumin, a constituent of turmeric, may increase tramadol's maximum concentration (Cmax) by inhibiting metabolism, while continued daily use for 7 days may reduce the area under the curve (AUC) due to the induction of drug-metabolizing enzymes such as cytochrome P450 3A4 (CYP3A4). However, this interaction has not been reported in humans.

Turmeric might increase the risk of bleeding with warfarin.
One case of increased international normalized ratio (INR) has been reported for a patient taking warfarin who began taking turmeric. Prior to taking turmeric, the patient had stable INR measurements. Within a few weeks of starting turmeric supplementation, the patient's INR increased to 10. Additionally, curcumin, the active constituent in turmeric, has demonstrated antiplatelet effects in vitro, which may produce additive effects when taken with warfarin.

Theoretically, turmeric might increase levels of drugs metabolized by CYP1A2. However, research is conflicting.
In vitro and animal research show that the turmeric constituent, curcumin, inhibits CYP1A2. However, other in vitro research suggests that curcumin does not significantly affect CYP1A2.

Theoretically, turmeric might increase blood levels of oral docetaxel.
Animal research suggests that the turmeric constituent, curcumin, enhances the oral bioavailability of docetaxel. However, the significance of this interaction is unclear, as this drug is typically administered intravenously in clinical settings.

Theoretically, large amounts of turmeric might interfere with hormone replacement therapy through competition for estrogen receptors.
In vitro research shows that curcumin, a constituent of turmeric, displaces the binding of estrogen to its receptors.

Theoretically, taking turmeric and glyburide in combination might increase the risk of hypoglycemia.
Clinical research shows that taking curcumin 475 mg daily for 10 days prior to taking glyburide 5 mg increases blood levels of glyburide by 12% at 2 hours after the dose in patients with type 2 diabetes. While maximal blood concentrations of glyburide were not affected, turmeric modestly decreased postprandial glucose levels for up to 24 hours when compared to glyburide alone, possibly due to the hypoglycemic effect of turmeric demonstrated in animal research.

Theoretically, turmeric might increase the effects of losartan.
Research in hypertensive rats shows that taking turmeric can increase the hypotensive effects of losartan.

Theoretically, turmeric might increase the effects and adverse effects of norfloxacin.
Animal research shows that taking curcumin, a turmeric constituent, can increase blood levels of orally administered norfloxacin.

Theoretically, turmeric might increase the absorption of P-glycoprotein substrates.
In vitro and animal research shows that curcuminoids and other constituents found in turmeric can inhibit P-glycoprotein expression and activity.

Theoretically, turmeric might alter blood levels of paclitaxel, although any effect may not be clinically relevant.
Clinical research in adults with breast cancer receiving intravenous paclitaxel suggests that taking turmeric may modestly alter paclitaxel pharmacokinetics. Patients received paclitaxel on day 1, followed by either no treatment or turmeric 2 grams daily from days 2-22. Pharmacokinetic modeling suggests that turmeric reduces the maximum concentration and area under the curve of paclitaxel by 12.1% and 7.7%, respectively. However, these changes are not likely to be considered clinically relevant. Conversely, animal research suggests that curcumin, a constituent of turmeric, enhances the oral bioavailability of paclitaxel. However, the significance of this interaction is unclear, as this drug is typically administered intravenously in clinical settings.

Goji can increase the effects of warfarin and possibly increase the risk of bleeding.
There are at least 5 case reports of increased international normalized ratio (INR) in patients stabilized on warfarin who began drinking goji juice, concentrated goji tea, or goji wine. Goji may inhibit the metabolism of warfarin by cytochrome P450 2C9 (CYP2C9).

Theoretically, concomitant use of goji root bark, but not goji fruit, with antihypertensive drugs might have additive effects.
Animal and in vitro research suggest that goji root bark has hypotensive effects. However, goji fruit juice does not appear to reduce systolic or diastolic blood pressure in humans.

Theoretically, goji berry might inhibit CYP2C19 and reduce metabolism of CYP2C19 substrates.
In vitro research shows that goji berry tincture and juice inhibit CYP2C19 enzymes. Concomitant use with goji may decrease metabolism and increase levels of CYP2C19 substrates. However, this has not been reported in humans.

Theoretically, goji berry might inhibit CYP2C9 and reduce metabolism of CYP2C9 substrates.
In vitro research shows that goji berry tincture and juice inhibit CYP2C9 enzymes. Additionally, multiple case reports suggest that goji berry concentrated tea and juice inhibit the metabolism of warfarin, a CYP2C9 substrate. Concomitant use with goji may decrease metabolism and increase levels of CYP2C9 substrates.

Theoretically, goji berry might inhibit CYP2D6 and reduce metabolism of CYP2D6 substrates.
In vitro research shows that goji berry juice inhibits CYP2D6 enzymes. Concomitant use with goji may decrease metabolism and increase levels of CYP2D6 substrates. However, this has not been reported in humans.

Theoretically, goji berry might inhibit CYP3A4 and reduce metabolism of CYP3A4 substrates.
In vitro research shows that goji berry juice inhibits CYP3A4 enzymes. Concomitant use with goji may decrease metabolism and increase levels of CYP3A4 substrates. However, this has not been reported in humans.

Theoretically, goji berry might increase the levels and clinical effects of flecainide.
In one case report, a 75-year-old patient stable on flecainide and warfarin presented to the emergency room with fainting and pleomorphic arrhythmia caused by flecainide toxicity. Flecainide toxicity was attributed to drinking 1-2 glasses of concentrated goji tea daily for 2 weeks. Theoretically, goji may have inhibited the cytochrome P450 2D6 (CYP2D6) metabolism of flecainide.

Theoretically, concomitant use of goji fruit polysaccharides or goji root bark with antidiabetes drugs might have additive effects.
Animal and in vitro research show that goji root bark and fruit polysaccharides might have hypoglycemic effects. However, clinical research has only shown that taking goji fruit polysaccharides with or without antidiabetes drugs modestly reduces postprandial glucose when compared with control, with no reports of hypoglycemia.

Theoretically, grape extracts may have antiplatelet effects and may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
In vitro evidence suggests that grape extracts might decrease platelet aggregation.

Ingesting grape juice with cyclosporine can reduce cyclosporine absorption.
A small pharmacokinetic study in healthy young adults shows that intake of purple grape juice 200 mL along with cyclosporine can decrease the absorption of cyclosporine by up to 30% when compared with water. Separate doses of grape juice and cyclosporine by at least 2 hours to avoid this interaction.

Theoretically, grape juice might reduce the levels of CYP1A2 substrates.
A small pharmacokinetic study in healthy adults shows that ingestion of 200 mL of grape juice decreases phenacetin plasma levels. This is thought to be due to induction of CYP1A2.

Theoretically, grape seed extract may increase the levels of CYP2D6 substrates.
In vitro evidence suggests that grape seed extract might inhibit CYP2D6 enzymes. However, this interaction has not been reported in humans.

Theoretically, grape seed extract might increase the levels of CYP2E1 substrates.
In vitro and animal research suggests that grape seed proanthocyanidin extract inhibits CYP2E1 enzymes. However, this interaction has not been reported in humans.

It is unclear if grape seed extract inhibits or induces CYP3A4; research is conflicting.
In vitro evidence suggests that grape seed extract might inhibit CYP3A4 enzymes. However, evidence from animal research shows that grape seed extract may induce CYP3A4 in the liver. So far, these interactions have not been reported in humans.

Theoretically, long-term intake of grape seed extract might decrease the effects of midazolam.
Animal research shows that subchronic ingestions of grape seed extract can increase the elimination of intravenous midazolam by increasing hepatic CYP3A4 activity. Single doses of grape seed extract do not appear to affect midazolam elimination.

Grape juice might decrease phenacetin absorption.
A small pharmacokinetic study in healthy adults shows that ingestion of 200 mL of grape juice decreases phenacetin plasma levels. This is thought to be due to induction of cytochrome P450 1A2 (CYP1A2).

It is unclear if grape juice or grape seed extract inhibits CYP2C9; research is conflicting.
In vitro evidence shows that grape seed extract or grape juice might inhibit CYP2C9 enzymes. However, a small pharmacokinetic study in healthy adults shows that drinking 8 ounces of grape juice once does not affect the clearance of flurbiprofen, a probe-drug for CYP2C9 metabolism. The effects of continued grape juice consumption are unclear.

Vitamin D might increase aluminum absorption and toxicity, but this has only been reported in people with renal failure.
The protein that transports calcium across the intestinal wall can also bind and transport aluminum. This protein is stimulated by vitamin D, which may therefore increase aluminum absorption. This mechanism may contribute to increased aluminum levels and toxicity in people with renal failure, when they take vitamin D and aluminum-containing phosphate binders chronically.

Vitamin D might reduce absorption of atorvastatin.
A small, low-quality clinical study shows that taking vitamin D reduces levels of atorvastatin and its active metabolites by up to 55%. However, while atorvastatin levels decreased, total cholesterol, low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol levels did not substantially change. Atorvastatin is metabolized in the gut by CYP3A4 enzymes, and researchers theorized that vitamin D might induce CYP3A4, causing reduced levels of atorvastatin. However, this proposed mechanism was not specifically studied.

Taking calcipotriene with vitamin D increases the risk for hypercalcemia.
Calcipotriene is a vitamin D analog used topically for psoriasis. It can be absorbed in sufficient amounts to cause systemic effects, including hypercalcemia. Theoretically, combining calcipotriene with vitamin D supplements might increase the risk of hypercalcemia.

Theoretically, hypercalcemia induced by high-dose vitamin D can increase the risk of arrhythmia from digoxin.
High doses of vitamin D can cause hypercalcemia. Hypercalcemia increases the risk of fatal cardiac arrhythmias with digoxin. Avoid vitamin D doses above the tolerable upper intake level (4000 IU daily for adults) and monitor serum calcium levels in people taking vitamin D and digoxin concurrently.

Theoretically, hypercalcemia induced by high-dose vitamin D can reduce the therapeutic effects of diltiazem for arrhythmia.
High doses of vitamin D can cause hypercalcemia. Hypercalcemia can reduce the effectiveness of verapamil in atrial fibrillation. Theoretically this could also occur with diltiazem. Avoid vitamin D doses above the tolerable upper intake level (4000 IU daily for adults) and monitor serum calcium levels in people taking vitamin D and diltiazem concurrently.

Theoretically, taking thiazide diuretics and high-dose vitamin D can increase the risk of hypercalcemia.
Thiazide diuretics decrease urinary calcium excretion, which could lead to hypercalcemia if vitamin D supplements are taken concurrently. This has been reported in people being treated with vitamin D for hypoparathyroidism, and also in elderly people with normal parathyroid function who were taking a thiazide, vitamin D, and calcium-containing antacids daily.

Hypercalcemia induced by high-dose vitamin D can reduce the therapeutic effects of verapamil for arrhythmia.
Hypercalcemia due to high doses of vitamin D can reduce the effectiveness of verapamil in atrial fibrillation. Avoid vitamin D doses above the tolerable upper intake level (4000 IU daily for adults) and monitor serum calcium levels in people taking vitamin D and verapamil concurrently.

Vitamin D might induce CYP3A4 enzymes and reduce the bioavailability of CYP3A4 substrates.
There is some concern that vitamin D might induce CYP3A4. In vitro research suggests that vitamin D induces CYP3A4 transcription. Additionally, observational research has found that increased UV light exposure and serum vitamin D levels are associated with decreased serum levels of CYP3A4 substrates such as tacrolimus and sirolimus, while no association between UV light exposure or vitamin D levels and levels of mycophenolic acid, a non-CYP3A4 substrate, was found. A small, low-quality clinical study shows that taking vitamin D reduces levels of the CYP3A4 substrate atorvastatin and its active metabolites by up to 55%; however, the clinical effects of atorvastatin were not reduced. While researchers theorized that vitamin D might induce CYP3A4, this proposed mechanism was not specifically studied.

Theoretically, concomitant use might increase the risk for simulant adverse effects.
Black tea contains caffeine. There is evidence that using ephedrine with caffeine might increase the risk of serious life-threatening or debilitating adverse effects such as hypertension, myocardial infarction, stroke, seizures, and death. Tell patients to avoid taking caffeine with ephedrine and other stimulants.

Theoretically, black tea might decrease the vasodilatory effects of adenosine and interfere with its use prior to stress testing.
Black tea contains caffeine. Caffeine is a competitive inhibitor of adenosine at the cellular level. However, caffeine does not seem to affect supplemental adenosine because high interstitial levels of adenosine overcome the antagonistic effects of caffeine. It is recommended that methylxanthines such as caffeine, as well as methylxanthine-containing products, be stopped 24 hours prior to pharmacological stress tests. However, methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing.

Theoretically, black tea may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Black tea contains caffeine. Caffeine is reported to have antiplatelet activity. Theoretically, the caffeine in black tea might increase the risk of bleeding when used concomitantly with antiplatelet drugs. However, this interaction has not been reported in humans.

Theoretically, concomitant use of large amounts of black tea might increase cardiac inotropic effects of beta-agonists.
Black tea contains caffeine. Caffeine can increase cardiac inotropic effects of beta-agonists.

Theoretically, black tea might reduce the effects of carbamazepine and increase the risk for convulsion.
Black tea contains caffeine. Animal research suggests that caffeine can lower the anticonvulsant effects of carbamazepine and can induce seizures when taken in doses above 400 mg/kg. Human research has shown that taking caffeine 300 mg in three divided doses along with carbamazepine 200 mg reduces the bioavailability of carbamazepine by 32% and prolongs the plasma half-life of carbamazepine 2-fold in healthy individuals.

Theoretically, concomitant use might increase the effects and adverse effects of caffeine in black tea.
Black tea contains caffeine. Cimetidine can reduces caffeine clearance by 31% to 42%.

Theoretically, black tea might increase the levels and adverse effects of clozapine and acutely exacerbate psychotic symptoms.
Concomitant administration of black tea and clozapine might theoretically cause acute exacerbation of psychotic symptoms due to the caffeine in black tea. Caffeine can increase the effects and toxicity of clozapine. Caffeine doses of 400-1000 mg daily inhibit clozapine metabolism. Clozapine is metabolized by cytochrome P450 1A2 (CYP1A2). Researchers speculate that caffeine might inhibit CYP1A2. However, there is no reliable evidence that caffeine affects CYP1A2. There is also speculation that genetic factors might make some patients be more sensitive to the interaction between clozapine and caffeine.

Theoretically, concomitant use might increase the effects and adverse effects of caffeine found in black tea.
Black tea contains caffeine. Oral contraceptive drugs can decrease caffeine clearance by 40% to 65%.

Theoretically, concomitant use might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Caffeine is metabolized by CYP1A2,. Theoretically, drugs that inhibit CYP1A2 may decrease the clearance rate of caffeine from black tea and increase caffeine levels.

Theoretically, black tea might decrease the vasodilatory effects of dipyridamole and interfere with its use prior to stress testing.
Black tea contains caffeine. Caffeine is a methylxanthine that may inhibit dipyridamole-induced vasodilation. It is recommended that methylxanthines such as caffeine, as well as methylxanthine-containing products such as black tea, be stopped 24 hours prior to pharmacological stress tests. Methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing.

Theoretically, disulfiram might increase the risk of adverse effects from caffeine.
Black tea contains caffeine. In human research, disulfiram decreases the clearance and increases the half-life of caffeine.

Theoretically, using black tea with diuretic drugs might increase the risk of hypokalemia.
Black tea contains caffeine. Caffeine, especially in excessive amounts, can reduce potassium levels due to stimulation of the sodium-potassium pump. Diuretics can also cause lower potassium levels.

Theoretically, estrogens might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Estrogen inhibits caffeine metabolism.

Theoretically, black tea might reduce the effects of ethosuximide and increase the risk for convulsions.
Black tea contains caffeine. Animal research suggests that caffeine 92.4 mg/kg can decrease the anticonvulsant activity of ethosuximide. However, this effect has not been observed in humans.

Theoretically, black tea might reduce the effects of felbamate and increase the risk for convulsions.
Black tea contains caffeine. Animal research suggests that a high dose of caffeine 161.7 mg/kg can decrease the anticonvulsant activity of felbamate. However, this effect has not been observed in humans.

Theoretically, black tea might increase the levels and adverse effects of flutamide.
Black tea contains caffeine. In vitro evidence suggests that caffeine can inhibit the metabolism of flutamide. Theoretically, concomitant use of caffeine and flutamide might increase serum concentrations of flutamide and increase the risk of adverse effects.

Theoretically, fluvoxamine might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Fluvoxamine reduces caffeine metabolism.

Theoretically, abrupt black tea withdrawal might increase the levels and adverse effects of lithium.
Black tea contains caffeine. Abrupt caffeine withdrawal can increase serum lithium levels. Two cases of lithium tremor that worsened with abrupt coffee withdrawal have been reported.

Theoretically, concomitant use might increase the risk of a hypertensive crisis.
Black tea contains caffeine. Caffeine has been shown to inhibit monoamine oxidase (MAO) A and B in laboratory studies. Concomitant intake of large amounts of caffeine with MAOIs might precipitate a hypertensive crisis. In a case report, a patient that consumed 10-12 cups of caffeinate coffee and took the MAOI tranylcypromine presented with severe hypertension. Hypertension was resolved after the patients switched to drinking decaffeinated coffee.

Theoretically, concomitant use might increase the risk of hypertension.
Black tea contains caffeine. Concomitant use of caffeine and nicotine has been shown to have additive cardiovascular effects, including increased heart rate and blood pressure. Blood pressure was increased by 10.8/12.4 mmHg when the agents were used concomitantly.

Theoretically, black tea might reduce the absorption of organic anion-transporting polypeptide (OATP) substrates.
In vitro, black tea extract inhibits organic anion-transporting polypeptide (OATP)2B1. OATP2B1 is expressed in the small intestine and liver and is responsible for the uptake of drugs and other compounds. In an animal model, black tea extract was found to inhibit the absorption of rosuvastatin, a substrate of OATP2B1. However, this effect has not been reported in humans.

Theoretically, black tea might decrease the effects of pentobarbital.
Black tea contains caffeine. Theoretically, caffeine might negate the hypnotic effects of pentobarbital.

Theoretically, black tea might reduce the effects of phenobarbital and increase the risk for convulsions.
Black tea contains caffeine. Animal research suggests that caffeine can decrease the anticonvulsant activity of phenobarbital. The exact mechanism of this interaction is unclear.

Theoretically, phenylpropanolamine might increase the risk of hypertension, as well as the levels and adverse effects of caffeine.
Black tea contains caffeine. Concomitant use of phenylpropanolamine and caffeine might cause an additive increase in blood pressure. Phenylpropanolamine also seems to increase caffeine serum levels.

Theoretically, black tea might reduce the effects of phenytoin and increase the risk for convulsions.
Black tea contains caffeine. Animal research suggests that caffeine can decrease the anticonvulsant activity of phenytoin. The effect does not seem to be related to the seizure threshold-lowering effects of caffeine. However, the exact mechanism of this interaction is unclear.

Theoretically, concomitant use might increase the risk for stimulant adverse effects.
Guarana contains caffeine. Use of ephedrine with caffeine can increase the risk of stimulatory adverse effects. There is evidence that using ephedrine with caffeine might increase the risk of serious life-threatening or debilitating adverse effects such as hypertension, myocardial infarction, stroke, seizures, and death.

Theoretically, guarana might decrease the vasodilatory effects of adenosine and interfere with its use prior to stress testing.
Guarana contains caffeine. Caffeine is a competitive inhibitor of adenosine at the cellular level. However, caffeine does not seem to affect supplemental adenosine because high interstitial levels of adenosine overcome the antagonistic effects of caffeine. It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests. However, methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing.

Theoretically, guarana may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
In vitro and animal research suggests that guarana extract can inhibit platelet aggregation. This effect may be due to the caffeine in guarana, which is also reported to have antiplatelet activity. This interaction has not been reported in humans.

Theoretically, concomitant use might increase the clinical effects of beta-adrenergic agonists.
Guarana contains caffeine. Theoretically, concomitant use of large amounts of caffeine might increase cardiac inotropic effects of beta-agonists.

Theoretically, guarana might reduce the effects of carbamazepine and increase the risk for convulsions.
Animal research suggests that taking caffeine can lower the anticonvulsant effects of carbamazepine and can induce seizures when given to animals in doses above 400 mg/kg. Human research has shown that taking caffeine 300 mg in three divided doses along with carbamazepine 200 mg reduces the bioavailability of carbamazepine by 32% and prolongs the plasma half-life of carbamazepine two-fold in healthy individuals.

Theoretically, concomitant use might increase the effects and adverse effects of caffeine in guarana.
Guarana contains caffeine. Cimetidine decreases the rate of caffeine clearance by 31% to 42%.

Theoretically, guarana might increase the levels and adverse effects of clozapine and acutely exacerbate psychotic symptoms.
Guarana contains caffeine. Caffeine can increase the effects and toxicity of clozapine. Caffeine doses of 400-1000 mg per day inhibit clozapine metabolism. Clozapine is metabolized by cytochrome P450 1A2 (CYP1A2). Researchers speculate that caffeine might inhibit CYP1A2. However, there is no reliable evidence that caffeine affects CYP1A2. There is also speculation that genetic factors might make some patients more sensitive to the interaction between clozapine and caffeine.

Theoretically, guarana might decrease the vasodilatory effects of dipyridamole and interfere with its use prior to stress testing.
Guarana contains caffeine. Caffeine might inhibit dipyridamole-induced vasodilation. It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests. Methylxanthines appear more likely to interfere with dipyridamole than adenosine-induced stress testing.

Theoretically, disulfiram might increase the risk of adverse effects from caffeine.
In human research, disulfiram decreases the clearance and increases the half-life of caffeine.

Theoretically, using guarana with diuretic drugs might increase the risk of hypokalemia.
Guarana contains caffeine. Caffeine, especially in excessive amounts, can reduce potassium levels due to stimulation of the sodium-potassium pump. Diuretics can also lower potassium levels.

Theoretically, estrogens might increase the levels and adverse effects of caffeine.
Guarana contains caffeine. Estrogen inhibits caffeine metabolism.

Theoretically, guarana might reduce the effects of ethosuximide and increase the risk for convulsions.
Guarana contains caffeine. Animal research shows that caffeine 92.4 mg/kg can decrease the anticonvulsant activity of ethosuximide. This effect has not been observed in humans.

Theoretically, guarana might reduce the effects of felbamate and increase the risk for convulsions.
Guarana contains caffeine. Animal research shows that a high dose of caffeine 161.7 mg/kg can decreases the anticonvulsant activity of felbamate. This effect has not been observed in humans.

Theoretically, guarana might increase the levels and adverse effects of flutamide.
Guarana contains caffeine. In vitro evidence shows that caffeine can inhibit the metabolism of flutamide. However, this effect has not been reported in humans.

Theoretically, fluvoxamine might increase the levels and adverse effects of caffeine.
Guarana contains caffeine. Fluvoxamine reduces caffeine metabolism.

Theoretically, abrupt guarana withdrawal might increase the levels and adverse effects of lithium.
Guarana contains caffeine. Theoretically, abrupt caffeine withdrawal might increase serum lithium levels. There are two case reports of lithium tremor that worsened upon abrupt coffee withdrawal.

Theoretically, concomitant use might increase the risk of a hypertensive crisis.
Guarana contains caffeine. Caffeine has been shown to inhibit MAO-A and -B in laboratory studies. Concomitant intake of large amounts of caffeine with MAOIs might precipitate a hypertensive crisis. In a case report, a patient that consumed 10-12 cups of caffeinated coffee and took the MAOI tranylcypromine presented with severe hypertension. Hypertension was resolved after the patient switched to drinking decaffeinated coffee.

Theoretically, concomitant use might increase the risk of hypertension.
Guarana contains caffeine. Concomitant use of caffeine and nicotine has been shown to have additive cardiovascular effects, including increased heart rate and blood pressure. Blood pressure was increased by 10.8/12.4 mmHg when the agents were used concomitantly.

Theoretically, guarana might decrease the effects of pentobarbital.
Guarana contains caffeine. In vivo evidence suggests that caffeine can negate the hypnotic effects of pentobarbital in humans. However, animal research suggests that guarana does not alter the hypnotic effect of pentobarbital.

Theoretically, guarana might reduce the effects of phenobarbital and increase the risk for convulsions.
Guarana contains caffeine. Animal research shows that caffeine can decrease the anticonvulsant activity of phenobarbital. The exact mechanism of this interaction is unclear.

Theoretically, phenylpropanolamine might increase the risk of hypertension, as well as the levels and adverse effects of caffeine.
Guarana contains caffeine. Concomitant use of phenylpropanolamine and caffeine might cause an additive increase in blood pressure. Phenylpropanolamine also seems to increase caffeine serum levels.

Theoretically, guarana might reduce the effects of phenytoin and increase the risk for convulsions.
Guarana contains caffeine. Animal research shows that caffeine can decrease the anticonvulsant activity of phenytoin. The effect does not seem to be related to the seizure threshold-lowering effects of caffeine. However, the exact mechanism of this interaction is unclear.

Theoretically, guarana might increase the levels and clinical effects of pioglitazone.
Guarana contains caffeine. Animal research suggests that caffeine can modestly increase the maximum concentration, area under the curve, and half-life of pioglitazone, and also reduce its clearance. This increased the antidiabetic effects of pioglitazone. However, the exact mechanism of this interaction is unclear.

Theoretically, concomitant use might increase the levels and adverse effects of both caffeine and riluzole.
Guarana contains caffeine. Caffeine and riluzole are both metabolized by cytochrome P450 1A2 (CYP1A2), and concomitant use might reduce the metabolism of one or both agents.

Theoretically, concomitant use might increase stimulant adverse effects.
Guarana contains caffeine. Due to the central nervous system (CNS) stimulant effects of caffeine, concomitant use with stimulant drugs can increase the risk of adverse effects.

Theoretically, chlorella might have additive effects with photosensitizing drugs.
Chlorella has been reported to cause photosensitization. In five case reports, patients who had ingested chlorella exhibited swelling followed by erythematopurpuric lesions on sun-exposed areas of the body. Theoretically, concomitant use with photosensitizing drugs may exacerbate effects.

Theoretically, chlorella might reduce the clinical effects of warfarin.
Chlorella contains significant amounts of vitamin K. There is at least one case report of warfarin therapy becoming sub-therapeutic after initiation of chlorella supplements.

Theoretically, spirulina blue-green algae might increase the risk of bleeding if used with other anticoagulant or antiplatelet drugs. However, this is unlikely.
Spirulina blue-green algae have shown antiplatelet and anticoagulant effects in vitro. However, one preliminary study in 24 patients receiving spirulina blue-green algae 2.3 grams daily for 2 weeks showed no effect on platelet activation or measures of clotting time.

Theoretically, taking blue-green algae with antidiabetes drugs might increase the risk of hypoglycemia.
Human research shows that spirulina blue-green algae can have hypoglycemic effects in patients with diabetes, at least some of whom were using antidiabetes drugs. However, blue-green algae does not seem to improve glycated hemoglobin (HbA1c) levels in patients with diabetes. A meta-analysis of animal studies also suggests that spirulina blue-green algae have hypoglycemic effects.

Theoretically, concurrent use of blue-green algae might interfere with immunosuppressive therapy.
Blue-green algae have been shown to stimulate the immune system.

Theoretically, taking wheatgrass with antidiabetes drugs might lower blood glucose levels and increase the risk of hypoglycemia.
Animal research shows that taking wheatgrass stimulates the release of insulin from beta-cells and lowers blood glucose.

Theoretically, wheatgrass might decrease the levels and clinical effects of CYP1A2 substrates.
In vitro research shows that wheatgrass induces CYP1A2 enzymes.

Consuming sweet orange with celiprolol can decrease oral absorption of celiprolol.
A pharmacokinetic study in healthy volunteers shows that celiprolol levels, after a single dose of 100 mg, are decreased by up to 90% in people who drink sweet orange juice 200 mL three times daily. It's not known if lower consumption of sweet orange juice will have the same effect. Theoretically, this occurs due to short-term inhibition of organic anion transporting polypeptide (OATP). Recommend separating drug administration and consumption of sweet orange by at least 4 hours.

Consuming sweet orange juice with ivermectin can decrease the oral absorption of ivermectin.
A pharmacokinetic study in healthy volunteers shows that taking ivermectin orally with sweet orange juice 750 mL over 4 hours reduces the bioavailability of ivermectin. This effect does not seem to be related to effects on P-glycoprotein. The effect on ivermectin is more pronounced in males compared to females.

Consuming sweet orange juice can decrease oral absorption of OATP substrates. Separate administration by at least 4 hours.
Clinical research shows that consuming sweet orange juice inhibits OATP, which reduces bioavailability of oral drugs that are substrates of OATP. For example, sweet orange juice decreases bioavailability of fexofenadine, a substrate of OATP, by about 72% and of celiprolol, another OATP substrate, by up to 90%. Since sweet orange juice seems to affect OATP for a short time, recommend separating drug administration and consumption of sweet orange juice by at least 4 hours.

Consuming sweet orange juice with pravastatin can increase the absorption of pravastatin.
A small pharmacokinetic study in healthy volunteers shows that consuming sweet orange juice 800 mL over 3 hours, including before, during, and after taking pravastatin 10 mg, increases pravastatin levels by about 149%, without affecting pravastatin elimination. Theoretically this effect might be due to modulation of organic anion transporting polypeptides (OATPs) by sweet orange juice. Sweet orange juice does not seem to affect simvastatin levels, but it is not known if sweet orange affects any of the other statins.

Consuming sweet orange juice with fexofenadine can decrease oral absorption of fexofenadine.
Clinical research shows that coadministration of sweet orange juice 1200 mL decreases bioavailability of fexofenadine by about 72%. In an animal model, sweet orange juice decreased bioavailability of fexofenadine by 31%. Fexofenadine manufacturer data indicates that concomitant administration of sweet orange juice and fexofenadine results in larger wheal and flare sizes in research models. This suggests that sweet orange reduces the clinical response to fexofenadine. Theoretically, this occurs due to short-term inhibition of organic anion transporting polypeptide (OATP). Recommend separating drug administration and consumption of sweet orange by at least 4 hours.

Sweet orange juice seems to modulate P-glycoprotein (P-gp), which might affect the blood levels of P-gp substrates.
Animal and in vitro research suggest that orange juice extract inhibits drug efflux by P-gp, increasing absorption and levels of P-gp substrates. In contrast, pharmacokinetic research in humans shows that drinking large amounts of sweet orange juice decreases absorption and levels of the P-gp substrate celiprolol. This suggests that orange juice actually induces drug efflux by P-gp or affects drug levels by another mechanism such as inhibiting the gut drug transporter called organic anion transporting polypeptide (OATP). Until more is known, sweet orange juice should be used cautiously in people taking P-gp substrates.

Calcium-fortified sweet orange juice might reduce quinolone absorption.
Calcium binds to quinolones in the gut. Theoretically, the calcium in certain fortified orange juices can also bind to quinolone antibiotics and reduce their absorption and levels.

American ginseng seems to decrease the effectiveness of warfarin therapy.
Healthy patients receiving warfarin 5 mg daily, who also take American ginseng 1 gram twice daily, seem to have a significantly reduced international normalized ratio (INR).

Theoretically, taking American ginseng with antidiabetes drugs might increase the risk of hypoglycemia.
American ginseng seems to lower postprandial blood glucose. Theoretically, concomitant use with antidiabetes drugs might enhance blood glucose lowering effects and possibly cause hypoglycemia.

Theoretically, American ginseng use might interfere with immunosuppressive therapy.
American ginseng seems to stimulate immune function. Theoretically, American ginseng might decrease the effectiveness of immunosuppressant drugs.

Theoretically, American ginseng can interfere with MAOI therapy.
There is one case report of insomnia, headache, and tremors when an unspecified ginseng product was used with phenelzine (Nardil), an MAOI. There is also one case report of hypomania when an unspecified ginseng product was used with phenelzine. Theoretically, American ginseng may interfere with MAOI therapy.

Theoretically, antioxidant effects of vitamin C might reduce the effectiveness of alkylating agents.
The use of antioxidants like vitamin C during chemotherapy is controversial. There is concern that antioxidants could reduce the activity of chemotherapy drugs that generate free radicals, such as cyclophosphamide, chlorambucil, carmustine, busulfan, and thiotepa. In contrast, some researchers theorize that antioxidants might make chemotherapy more effective by reducing oxidative stress that could interfere with apoptosis (cell death) of cancer cells. More evidence is needed to determine what effect, if any, antioxidants such as vitamin C have on chemotherapy.

Vitamin C can increase the amount of aluminum absorbed from aluminum compounds.
Research in animals and humans shows that vitamin C increases aluminum absorption, theoretically by chelating aluminum and keeping it in solution where it is available for absorption. In people with normal renal function, urinary excretion of aluminum will likely increase, making aluminum retention and toxicity unlikely. Patients with renal failure who take aluminum-containing compounds such as phosphate binders should avoid vitamin C supplements in doses above the recommended dietary allowances.

Theoretically, the antioxidant effects of vitamin C might reduce the effectiveness of antitumor antibiotics.
The use of antioxidants like vitamin C during chemotherapy is controversial. There is concern that antioxidants could reduce the activity of chemotherapy drugs which generate free radicals, such as doxorubicin. In contrast, some researchers theorize that antioxidants might make chemotherapy more effective by reducing oxidative stress that could interfere with apoptosis (cell death) of cancer cells. More evidence is needed to determine what effects, if any, antioxidants such as vitamin C have on chemotherapy.

Vitamin C might increase blood levels of estrogens.
Increases in plasma estrogen levels of up to 55% occur under some circumstances when vitamin C is taken concurrently with oral contraceptives or hormone replacement therapy, including topical products. It is suggested that vitamin C prevents oxidation of estrogen in the tissues, regenerates oxidized estrogen, and reduces sulfate conjugation of estrogen in the gut wall. When tissue levels of vitamin C are high, these processes are already maximized and supplemental vitamin C does not have any effect on estrogen levels. Increases in plasma estrogen levels may occur when patients who are deficient in vitamin C take supplements. Monitor these patients for estrogen-related side effects.

Theoretically, vitamin C might decrease levels of fluphenazine.
In one patient there was a clinically significant decrease in fluphenazine levels when vitamin C (500 mg twice daily) was started. The mechanism is not known, and there is no further data to confirm this interaction.

Vitamin C can modestly reduce indinavir levels.
One pharmacokinetic study shows that taking vitamin C 1 gram orally once daily along with indinavir 800 mg orally three times daily reduces the area under the concentration-time curve of indinavir by 14%. The mechanism of this interaction is unknown, but it is unlikely to be clinically significant in most patients. The effect of higher doses of vitamin C on indinavir levels is unknown.

Vitamin C can increase levothyroxine absorption.
Two clinical studies in adults with poorly controlled hypothyroidism show that swallowing levothyroxine with a glass of water containing vitamin C 500-1000 mg in solution reduces thyroid stimulating hormone (TSH) levels and increases thyroxine (T4) levels when compared with taking levothyroxine alone. This suggests that vitamin C increases the oral absorption of levothyroxine, possibly due to a reduction in pH.

High-dose vitamin C might reduce the levels and effectiveness of warfarin.
Vitamin C in high doses may cause diarrhea and possibly reduce warfarin absorption. There are reports of two people who took up to 16 grams daily of vitamin C and had a reduction in prothrombin time. Lower doses of 5-10 grams daily can also reduce warfarin absorption. In many cases, this does not seem to be clinically significant. However, a case of warfarin resistance has been reported for a patient who took vitamin C 500 mg twice daily. Cessation of vitamin C supplementation resulted in a rapid increase in international normalized ratio (INR). Tell patients taking warfarin to avoid taking vitamin C in excessively high doses (greater than 10 grams daily). Lower doses may be safe, but the anticoagulation activity of warfarin should be monitored. Patients who are stabilized on warfarin while taking vitamin C should avoid adjusting vitamin C dosage to prevent the possibility of warfarin resistance.

High-dose vitamin C might slightly prolong the clearance of acetaminophen.
A small pharmacokinetic study in healthy volunteers shows that taking high-dose vitamin C (3 grams) 1.5 hours after taking acetaminophen 1 gram slightly increases the apparent half-life of acetaminophen from around 2.3 hours to 3.1 hours. Ascorbic acid competitively inhibits sulfate conjugation of acetaminophen. However, to compensate, elimination of acetaminophen glucuronide and unconjugated acetaminophen increases. This effect is not likely to be clinically significant.

Acidification of the urine by vitamin C might increase aspirin levels.
It has been suggested that acidification of the urine by vitamin C could increase reabsorption of salicylates by the renal tubules, and increase plasma salicylate levels. However, short-term use of up to 6 grams daily of vitamin C does not seem to affect urinary pH or salicylate excretion, suggesting this interaction is not clinically significant.

Acidification of the urine by vitamin C might increase choline magnesium trisalicylate levels.
It has been suggested that acidification of the urine by vitamin C could increase reabsorption of salicylates by the renal tubules, and increase plasma salicylate levels. However, short-term use of up to 6 grams daily of vitamin C does not seem to affect urinary pH or salicylate excretion, suggesting this interaction probably is not clinically significant.

Vitamin C might decrease the beneficial effects of niacin on high-density lipoprotein (HDL) cholesterol levels.
A combination of niacin and simvastatin (Zocor) effectively raises HDL cholesterol levels in patients with coronary disease and low HDL levels. Clinical research shows that taking a combination of antioxidants (vitamin C, vitamin E, beta-carotene, and selenium) along with niacin and simvastatin (Zocor) attenuates this rise in HDL, specifically the HDL-2 and apolipoprotein A1 fractions, by more than 50% in patients with coronary disease. It is not known whether this adverse effect is due to a single antioxidant such as vitamin C, or to the combination. It also is not known whether it will occur in other patient populations.

Acidification of the urine by vitamin C might increase salsalate levels.
It has been suggested that acidification of the urine by vitamin C could increase reabsorption of salicylates by the renal tubules, and increase plasma salicylate levels. However, short-term use of up to 6 grams/day vitamin C does not seem to affect urinary pH or salicylate excretion, suggesting this interaction probably is not clinically significant.

Theoretically, zinc might decrease levels of bictegravir/emtricitabine/tenofovir alafenamide by reducing its absorption.
Advise patients that bictegravir/emtricitabine/tenofovir alafenamide should be taken at least 2 hours before or 6 hours after zinc containing products.

Zinc might decrease cephalexin levels by chelating with cephalexin in the gut and preventing its absorption.
A pharmacokinetic study shows that zinc sulfate 250 mg taken concomitantly with cephalexin 500 mg decreases peak levels of cephalexin by 31% and reduces the exposure to cephalexin by 27%. Also, taking zinc sulfate 3 hours before cephalexin decreases peak levels of cephalexin by 11% and reduces the exposure to cephalexin by 18%. By decreasing cephalexin levels, zinc might increase the risk of treatment failure. This effect does not occur when zinc is taken 3 hours after the cephalexin dose. To avoid an interaction, advise patients take zinc sulfate 3 hours after taking cephalexin.

Theoretically, zinc might interfere with the therapeutic effects of cisplatin.
Animal research suggests that zinc stimulates tumor cell production of the protein metallothionein, which binds and inactivates cisplatin. It is not known whether zinc supplements or high dietary zinc intake can cause clinically significant interference with cisplatin therapy. Cisplatin might also increase zinc excretion.

Theoretically, taking zinc along with integrase inhibitors might decrease the levels and clinical effects of these drugs.
Zinc is a divalent cation. Pharmacokinetic studies have shown that other divalent cations such as calcium and iron can decrease blood levels of the integrase inhibitor dolutegravir through chelation.

Zinc might reduce the levels and clinical effects of penicillamine.
By forming an insoluble complex with penicillamine, zinc interferes with penicillamine absorption and activity. Zinc supplements reduce the efficacy of low-dose penicillamine (0.5-1 gram/day), but do not seem to affect higher doses (1-2.75 gram/day), provided dosing times are separated. Advise patients to take zinc and penicillamine at least 2 hours apart.

Zinc can decrease the levels and clinical effects of quinolones antibiotics.
Quinolones form complexes with zinc in the gastrointestinal tract, reducing absorption of both the quinolone and zinc if taken at the same time. Advise patients to take these drugs at least 2 hours before, or 4-6 hours after, zinc supplements.

Zinc modestly reduces levels of ritonavir.
Clinical research shows that zinc might reduce serum ritonavir levels by chelating with ritonavir in the gut and preventing its absorption. In patients with HIV, ritonavir is taken with atazanavir to prevent the metabolism and increase the effects of atazanavir. A pharmacokinetic study shows that, in patients being treated with atazanavir/ritonavir, co-administration of zinc sulfate (Solvazinc tablets) 125 mg as a single dose or as multiple daily doses for 2 weeks reduces plasma levels of ritonavir by about 16%. However, atazanavir levels still remains high enough to prevent HIV virus replication. Therefore, the decrease in ritonavir levels is not likely to be clinically significant.

Zinc might reduce levels of tetracycline antibiotics.
Tetracyclines form complexes with zinc in the gastrointestinal tract, which can reduce absorption of both the tetracycline and zinc when taken at the same time. Taking zinc sulfate 200 mg with tetracycline reduces absorption of the antibiotic by 30% to 40%. Demeclocycline and minocycline cause a similar interaction. However, doxycycline does not seem to interact significantly with zinc. Advise patients to take tetracyclines at least 2 hours before, or 4-6 hours after, zinc supplements to avoid any interactions.

Amiloride can modestly reduce zinc excretion and increase zinc levels.
Clinical research shows that amiloride can reduce urinary zinc excretion, especially at doses of 10 mg per day or more. This zinc-sparing effect can help to counteract zinc losses caused by thiazide diuretics, but it is unlikely to cause zinc toxicity at usual amiloride doses. The other potassium-sparing diuretics, spironolactone (Aldactone) and triamterene (Dyrenium), do not seem to have a zinc-sparing effect.

Zinc modestly reduces levels of atazanavir, although this effect does not seem to be clinically significant.
Clinical research shows that zinc might decrease serum atazanavir levels by chelating with atazanavir in the gut and preventing its absorption. Although a single dose of zinc sulfate (Solvazinc tablets) 125 mg orally does not affect atazanavir concentrations in patients being treated with atazanavir/ritonavir, co-administration of zinc sulfate 125 mg daily for 2 weeks reduces plasma levels of atazanavir by about 22% in these patients. However, despite this decrease, atazanavir levels still remain at high enough concentrations for the prevention of HIV virus replication.