Herb & supplement monograph

Black Tea Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Black Tea interacts with medications. The heart of this page is the interaction list — every drug Black Tea is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Black Tea is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Black Tea Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Black Tea drug interaction is moderate for most people, and it comes almost entirely from the caffeine in the tea. Only a small handful of the many listed interactions are rated major, and most of the rest are moderate caffeine-related effects that depend on how much tea is consumed.

Interactions deserving the most attention

The combination we take most seriously is black tea with ephedrine or similar stimulants, where added caffeine has been linked to dangerous rises in blood pressure and other serious harm. Seizure medicines also deserve care, since human research suggests caffeine can weaken the effect of carbamazepine, and animal studies raise the same question for related drugs. Caffeine can also raise levels or side effects of closely monitored medicines such as clozapine, and stopping heavy tea intake suddenly may affect lithium levels.

What the rest of the list means

Most of the hundreds of listed interactions are theoretical. Many rest on caffeine's possible effects on an enzyme the body uses to clear certain medications, or on lab and animal findings, and several predicted effects have not produced meaningful changes in people. For someone drinking moderate amounts of black tea, most combinations are unlikely to cause real problems.

Check your medications against Black Tea

Based on HelloPharmacist’s Black Tea interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Black Tea

694 medications have a known interaction with Black Tea, graded by severity. Select any drug for the full evidence-based detail.

8 major interactions. These combinations can be clinically significant — best avoided, or used only with close professional supervision. Always check with your pharmacist before combining them with Black Tea.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Black Tea using our pharmacist-reviewed interaction data.

AI summaries are generated from our Black Tea interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Black Tea combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Black Tea affects

Every type of medication (drug category) Black Tea is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 46 drug categories Black Tea interacts with

EphedrineAdenosine (adenocard)Anticoagulant/antiplatelet DrugsBeta-adrenergic AgonistsCarbamazepine (tegretol)Cimetidine (tagamet)Clozapine (clozaril)Contraceptive DrugsCytochrome P450 1a2 (cyp1a2) InhibitorsDipyridamole (persantine)Disulfiram (antabuse)Diuretic DrugsEstrogensEthosuximide (zarontin)Felbamate (felbatol)Flutamide (eulexin)Fluvoxamine (luvox)LithiumMonoamine Oxidase Inhibitors (maois)NicotineOrganic Anion-transporting Polypeptide Substrates (oatp)Pentobarbital (nembutal)Phenobarbital (luminal)PhenylpropanolaminePhenytoin (dilantin)Pioglitazone (actos)Quinolone AntibioticsRiluzole (rilutek)Rosuvastatin (crestor)Stimulant DrugsTheophyllineValproateVerapamil (calan, Others)Warfarin (coumadin)Alcohol (ethanol)Antidiabetes DrugsFluconazole (diflucan)Flurbiprofen (ansaid, Others)Metformin (glucophage)Methoxsalen (oxsoralen)Mexiletine (mexitil)PhenothiazinesTerbinafine (lamisil)Tiagabine (gabitril)Ticlopidine (ticlid)Tricyclic Antidepressants (tcas)

Ephedrine

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.

Likelihood Probable Evidence D

Adenosine (Adenocard)

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.

Likelihood Possible Evidence B

Anticoagulant/Antiplatelet Drugs

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.

Likelihood Possible Evidence D

Beta-Adrenergic Agonists

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.

Likelihood Probable Evidence D

Carbamazepine (Tegretol)

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.

Likelihood Possible Evidence B

Cimetidine (Tagamet)

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%.

Likelihood Likely Evidence B

Clozapine (Clozaril)

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.

Likelihood Possible Evidence B

Contraceptive Drugs

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%.

Likelihood Probable Evidence B

Cytochrome P450 1A2 (Cyp1A2) Inhibitors

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.

Likelihood Possible Evidence D

Dipyridamole (Persantine)

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.

Likelihood Probable Evidence B

Disulfiram (Antabuse)

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.

Likelihood Probable Evidence B

Diuretic Drugs

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.

Likelihood Possible Evidence D

Estrogens

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

Likelihood Probable Evidence B

Ethosuximide (Zarontin)

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.

Likelihood Possible Evidence D

Felbamate (Felbatol)

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.

Likelihood Possible Evidence D

Flutamide (Eulexin)

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.

Likelihood Possible Evidence D

Fluvoxamine (Luvox)

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

Likelihood Probable Evidence B

Lithium

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.

Likelihood Probable Evidence D

Monoamine Oxidase Inhibitors (Maois)

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.

Likelihood Possible Evidence D

Nicotine

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.

Likelihood Probable Evidence B

Organic Anion-Transporting Polypeptide Substrates (Oatp)

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.

Likelihood Possible Evidence D

Pentobarbital (Nembutal)

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

Likelihood Possible Evidence B

Phenobarbital (Luminal)

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.

Likelihood Possible Evidence D

Phenylpropanolamine

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.

Likelihood Probable Evidence B

Phenytoin (Dilantin)

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.

Likelihood Possible Evidence D

Pioglitazone (Actos)

Theoretically, black tea might increase the levels and clinical effects of pioglitazone.
Black tea 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 could increase the antidiabetic effects of pioglitazone. However, the exact mechanism of this interaction is unclear.

Likelihood Possible Evidence D

Quinolone Antibiotics

Theoretically, quinolone antibiotics might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Concomitant use of caffeine and quinolones can decrease caffeine clearance and increase effects and risk of adverse effects.

Likelihood Probable Evidence B

Riluzole (Rilutek)

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

Likelihood Possible Evidence D

Rosuvastatin (Crestor)

Theoretically, concomitant use might decrease the levels and clinical effects of rosuvastatin.
In animals, taking black tea extract along with rosuvastatin reduces plasma levels of rosuvastatin by approximately 48%. In vitro, black tea extract was found to inhibit organic anion-transporting polypeptide (OATP)2B1, a protein expressed in the small intestine that is responsible for the uptake of rosuvastatin and other compounds. This effect has not been reported in humans.

Likelihood Possible Evidence D

Stimulant Drugs

Theoretically, concomitant use might increase stimulant adverse effects.
Black tea 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.

Likelihood Probable Evidence C

Theophylline

Theoretically, black tea might increase the levels and adverse effects of theophylline.
Black tea contains caffeine, which can increase theophylline levels.

Likelihood Probable Evidence B

Valproate

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

Likelihood Possible Evidence D

Verapamil (Calan, Others)

Theoretically, concomitant use might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Verapamil increases plasma caffeine concentrations by 25%.

Likelihood Possible Evidence D

Warfarin (Coumadin)

Consuming large amounts of black tea might decrease the effects of warfarin.
In one case, a 67-year-old female who took warfarin and who regularly consumed large amounts of black tea had a stable international normalized ratio (INR) of 1.7 to 2.7. However, the INR increased to 5 when tea consumption was discontinued. It is thought that the vitamin K content of black tea may have reduced the effects of warfarin. Monitor patients carefully who start or discontinue drinking black tea while taking warfarin.

Likelihood Possible Evidence D

Alcohol (Ethanol)

Theoretically, alcohol might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Concomitant use of alcohol and caffeine can increase caffeine serum concentrations and the risk of caffeine adverse effects. Alcohol reduces caffeine metabolism.

Likelihood Possible Evidence D

Antidiabetes Drugs

Theoretically, taking black tea with antidiabetes drugs might interfere with blood glucose control.
Black tea contains caffeine. Reports claim that caffeine might increase or decrease blood sugar levels. Also, some evidence in healthy individuals suggests that drinking black tea reduces blood sugar.

Likelihood Unlikely Evidence B

Fluconazole (Diflucan)

Theoretically, fluconazole might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Fluconazole decreases caffeine clearance by approximately 25%.

Likelihood Possible Evidence B

Flurbiprofen (Ansaid, Others)

Theoretically, black tea might decrease the metabolism of flurbiprofen.
In vitro research shows that black tea decreases the metabolism of flurbiprofen, a cytochrome P450 2C9 (CYP2C9) substrate, by about 10%. However, clinical research suggests that drinking black tea does not significantly affect flurbiprofen plasma levels, metabolism, or elimination.

Likelihood Unlikely Evidence B

Metformin (Glucophage)

Theoretically, metformin might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Animal research suggests that metformin can reduce caffeine metabolism. Theoretically, concomitant use can increase caffeine serum concentrations and the risk of caffeine adverse effects.

Likelihood Possible Evidence D

Methoxsalen (Oxsoralen)

Theoretically, methoxsalen might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Methoxsalen can reduce caffeine metabolism. Concomitant use can increase caffeine serum concentrations and the risk of caffeine adverse effects.

Likelihood Possible Evidence B

Mexiletine (Mexitil)

Theoretically, mexiletine might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Mexiletine can decrease caffeine elimination by 50%.

Likelihood Possible Evidence B

Phenothiazines

Theoretically, phenothiazines might increase the levels and adverse effects of caffeine. Also, black tea may bind to phenothiazines and reduce their absorption.
Black tea contains caffeine. Phenothiazines can reduce the metabolism of caffeine by inhibiting cytochrome P450 1A2 (CYP1A2). Additionally, the tannins in black tea may bind to phenothiazines in the gastrointestinal tract and reduce their absorption.

Likelihood Possible Evidence D

Terbinafine (Lamisil)

Theoretically, terbinafine might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. Terbinafine decreases the clearance of intravenous caffeine by 19%.

Likelihood Possible Evidence B

Tiagabine (Gabitril)

Theoretically, black tea might increase the levels and adverse effects of tiagabine.
Black tea contains caffeine. Animal research suggests that chronic caffeine administration can increase the serum concentrations of tiagabine. However, concomitant use does not seem to reduce the antiepileptic effects of tiagabine.

Likelihood Possible Evidence D

Ticlopidine (Ticlid)

Theoretically, ticlopidine might increase the levels and adverse effects of caffeine.
Black tea contains caffeine. In vitro evidence suggests that ticlopidine can inhibit caffeine metabolism. However, this effect has not been reported in humans.

Likelihood Possible Evidence D

Tricyclic Antidepressants (Tcas)

Theoretically, TCAs might bind with black tea constituents when taken at the same time.
In vitro research suggests that the tannins in black tea might cause precipitation of TCAs. However, this effect has not been reported in humans.

Likelihood Possible Evidence D

Monograph

Black Tea: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Black tea is a popular caffeinated drink made from the fully oxidized leaves of the Camellia sinensis plant, and it contains caffeine and antioxidant plant compounds. Moderate tea drinking is generally safe for most adults and may modestly support heart health and alertness, but it is not a proven treatment for any disease. If you are pregnant, breastfeeding, sensitive to caffeine, or taking medicines, talk to your pharmacist or doctor.

Scientific name: Camellia sinensis
Family: Theaceae
Part used: Leaves and leaf buds (fully oxidized)
Common forms: Brewed tea, tea bags, loose leaf, instant powder, capsules, and standardized extracts

People commonly use it for

Mental alertness and energy
Heart health support
Blood pressure and cholesterol
Digestive complaints
Weight management
Antioxidant support

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallLikely safe

Moderate amounts are generally safe for most healthy adults, but the caffeine can cause problems in large amounts.

PregnancyPossibly Safe

When used orally in moderate amounts. Due to the caffeine content of black tea, mothers should closely monitor their intake to ensure moderate consump...

Read the full pregnancy detail

BreastfeedingPossibly Safe

When used orally in moderate amounts. Due to the caffeine content of black tea, caffeine intake should be closely monitored. Breast milk concentration...

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Jump to a section

Overview

Black tea is one of the most widely consumed drinks in the world. It comes from the leaves of the Camellia sinensis plant, the same plant used to make green, white, and oolong tea. What makes black tea different is that the leaves are fully oxidized (exposed to air), which gives it a darker color and stronger flavor.

The tea plant grows in warm, humid regions, especially in countries like India, China, Sri Lanka, and Kenya. After harvesting, the leaves are withered, rolled, oxidized, and dried.

People drink black tea mainly for its taste and its caffeine, which provides a gentle energy and alertness boost. It is also taken in capsule or extract form by people looking for antioxidant or heart-health support.

How it works

Black tea contains several active compounds. The best known is caffeine, a stimulant that increases alertness and can mildly raise heart rate and blood pressure for a short time.

Tea also contains plant compounds called polyphenols, including theaflavins and thearubigins that form during oxidation, along with smaller amounts of catechins. These act as antioxidants, meaning they may help protect cells from a type of damage called oxidative stress.

Black tea also contains L-theanine, an amino acid that some research suggests may promote a calm, focused feeling. Much of the research on these compounds comes from laboratory and animal studies, so it is not always clear how strongly they affect the human body when you simply drink tea.

Effectiveness

Does Black Tea work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 33 uses evaluated

1 Likely effective 5 Possibly effective 8 Leans ineffective 19 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Likely Effective Mental alertness