Drug & supplement interaction

Green Tea + Cimetidine

Cimetidine brand names: Tagamet HB, Tagamet, Cimetidine Injection.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Cimetidine falls into 3 drug categories that Green Tea can interact with; the most serious is rated moderate. Theoretically, concomitant use might increase the levels and adverse effects of caffeine.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions3
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Green Tea and Cimetidine

These two interact in 3 distinct ways. Each one is explained separately below.

Why Are There 3 Interactions?

Green Tea interacts with whole categories of medication. Cimetidine falls into 3 of those categories, so it can interact with Green Tea in 3 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CYTOCHROME P450 1A2 (CYP1A2) INHIBITORS

1 of 3

Why this applies to Cimetidine

Cimetidine falls under CYTOCHROME P450 1A2 (CYP1A2) INHIBITORS — the group Green Tea interacts with.

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.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the thing to know about this pair: cimetidine slows down a liver enzyme called CYP1A2, and that same enzyme is what your body uses to clear caffeine. Green tea naturally contains caffeine, so while you're taking cimetidine, that caffeine may hang around a bit longer than usual.

In real life, this could mean the caffeine from green tea hits you a little harder. Think jitteriness, a racing heart, trouble sleeping, or feeling wired. Keep in mind this is a theoretical concern based on how the drugs work, not strong proof, and a normal cup or two of green tea is unlikely to cause trouble for most folks. Concentrated extracts or lots of caffeine are more likely to matter. If you notice these effects, chat with your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Weisburger JH. Tea and health: the underlying mechanisms. Proc Soc Exp Biol Med 1999;220:271-5. PubMed
  2. Hagg S, Spigset O, Mjorndal T, Dahlqvist R. Effect of caffeine on clozapine pharmacokinetics in healthy volunteers. Br J Clin Pharmacol 2000;49:59-63. PubMed
  3. Carrillo JA, Benitez J. Clinically significant pharmacokinetic interactions between dietary caffeine and medications. Clin Pharmacokinet 2000;39:127-53. PubMed
  4. Kot, M. and Daniel, W. A. Effect of diethyldithiocarbamate (DDC) and ticlopidine on CYP1A2 activity and caffeine metabolism: an in vitro comparative study with human cDNA-expressed CYP1A2 and liver microsomes. Pharmacol Rep. 2009;61(6):1216-1220. PubMed
  5. Wojcikowski, J. and Daniel, W. A. Perazine at therapeutic drug concentrations inhibits human cytochrome P450 isoenzyme 1A2 (CYP1A2) and caffeine metabolism--an in vitro study. Pharmacol Rep. 2009;61(5):851-858. PubMed
  6. Wang, X. and Yeung, J. H. Effects of the aqueous extract from Salvia miltiorrhiza Bunge on caffeine pharmacokinetics and liver microsomal CYP1A2 activity in humans and rats. J Pharm Pharmacol 2010;62(8):1077-1083.
  7. Kot M, Daniel WA. Caffeine as a marker substrate for testing cytochrome P450 activity in human and rat. Pharmacol Rep 2008;60:789-97.
  8. Kjaerstad MB, Nielsen F, Nohr-Jensen L, et al. Systemic uptake of miconazole during vaginal suppository use and effect on CYP1A2 and CYP3A4 associated enzyme activities in women. Eur J Clin Pharmacol 2010;66:1189-97. PubMed
  9. Goh BC, Reddy NJ, Dandamudi UB, et al. An evaluation of the drug interaction potential of pazopanib, an oral vascular endothelial growth factor receptor tyrosine kinase inhibitor, using a modified Cooperstown 5+1 cocktail in patients with advanced solid t
  10. Chen Y, Kang Z, Yan J, et al. Liu wei di huang wan, a well-known traditional Chinese medicine induces CYP1A2 while suppressing CYP2A6 and N-acetyltransferase 2 acivities in man. J Ethnopharmacol 2010;132:213-8.
  11. Suzuki S, Murayama Y, Sugiyama E, et al. Estimating pediatric doses of drugs metabolized by cytochrome P450 (CYP) isozymes, based on physiological liver development and serum protein levels. Yakugaku Zasshi 2010;130:613-20. PubMed
  12. Chien CF, Wu YT, Lee WC, et al. Herb-drug interaction of Andrographis paniculata extract and andrographolide on the pharmacokinetics of theophylline in rats. Chem Biol Interact 2010;184:458-65. PubMed
  13. Mills BM, Zaya MJ, Walters RR, et al. Current cytochrome P450 phenotyping methods applied to metabolic drug -drug interaction prediction in dogs. Drug Metab Dispos 2010;38:396-404. PubMed
  14. Turpault S, Brian W, Van Horn R, et al. Pharmacokinetic assessment of a five-probe cocktail for CYPs 1A2, 2C9, 2C19, 2D6, and 3A. Br J Clin Pharmacol 2009;68:928-35. PubMed
  15. Filimonova AA, Ziganshina LE, Ziganshin AU, Chichirov AA. On the possibility of patient phenotyping on the basis of cytochrome p-450 1A2 isoenzyme activity using caffeine as the test substrate. Eksp Klin Farmakol 2009;72:61-5.
  16. Jenkins J, Williams D, Deng Y, et al. Eltrombopag, an oral thrombopoietin receptor agonist, has no impact on the pharmacokinetic profile of probe drugs for cytochrome P450 isoenzymes CYP3A4, CYP1A2, CYP2C9 and CYP2C19 in healthy men: a cocktail analysis.
  17. Perera, V., Gross, A. S., and McLachlan, A. J. Caffeine and paraxanthine HPLC assay for CYP1A2 phenotype assessment using saliva and plasma. Biomed.Chromatogr. 2010;24(10):1136-1144. PubMed
  18. Izzo, A. A. and Ernst, E. Interactions between herbal medicines and prescribed drugs: an updated systematic review. Drugs 2009;69(13):1777-1798. PubMed
Moderate

P-GLYCOPROTEIN SUBSTRATES

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Cimetidine also falls under P-GLYCOPROTEIN SUBSTRATES.

Green tea might increase the levels and adverse effects of P-glycoprotein (P-gp) substrates.
In vitro research and case reports suggest that green tea inhibits drug efflux by P-gp, potentially increasing serum levels of P-gp substrates. Case reports from the World Health Organization (WHO) adverse drug reaction database describe increased toxicity in patients taking green tea and certain P-gp substrates.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the idea with green tea and cimetidine. Your body uses a kind of cellular bouncer called P-glycoprotein (P-gp) to push certain drugs back out of cells and into the gut and urine. Compounds in green tea may slow that bouncer down a little, which could let a bit more cimetidine linger in your system than usual.

In practice, cimetidine is a pretty gentle, well-tolerated medicine, so even if levels nudge up, most people won't notice much. If anything, you might see more of its usual mild effects like headache, dizziness, or loose stools. Honestly, this is built on weak, anecdotal evidence, and a cup or two of tea is unlikely to matter much. Concentrated green tea extract pills are the bigger question, so run those by your pharmacist first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Pochet S, Lechon AS, Lescrainier C, et al. Herb-anticancer drug interactions in real life based on VigiBase, the WHO global database. Sci Rep 2022;12(1):14178. PubMed
Moderate

CIMETIDINE (Tagamet)

3 of 3
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%.
Severity Moderate Likelihood Likely Evidence B

Well-controlled human studies have demonstrated the likely existence of this interaction.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's a simple way to picture this one. Cimetidine (Tagamet) slows down the liver enzyme that normally clears caffeine out of your body, and green tea naturally contains caffeine. So when you pair the two, that caffeine can hang around longer than usual, building up by roughly a third or more. Cimetidine isn't a prodrug here, so the direction is straightforward: more caffeine staying active in your system.

In real life, that might mean feeling jittery, a racing heart, trouble sleeping, or a nervous, wired feeling, especially if you drink a lot of green tea or take concentrated extracts. A cup or two probably won't be a big deal for most folks. If you notice these symptoms, chat with your pharmacist or doctor before changing anything.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. May DC, Jarboe CH, VanBakel AB, Williams WM. Effects of cimetidine on caffeine disposition in smokers and nonsmokers. Clin Pharmacol Ther 1982;31:656-61. PubMed

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction 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.
  • PossibleInteraction 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.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Green Tea Also Interacts With Other Medications

Green Tea has 13 major, 904 moderate, 375 minor known drug interactions in our database — the Cimetidine one above is among them. If you take anything else, check it against the full list below.

Major 13 Moderate 904 Minor 375 No known interaction 1,538 (incl. Cimetidine)
Taking anything else?

Check Another of Your Medications Against Green Tea

Covers the 2,830 medications we’ve checked against Green Tea. Pick one to open its full report.

From our Q&A

Questions About Green Tea or Cimetidine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Green Tea or Cimetidine, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Cimetidine

This page covers Green Tea only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Cimetidine page lists 95 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Pu-erh Tea (major), St. John's Wort (major), Adrafinil (moderate) and African Wild Potato (moderate).

By severity: 3 major · 63 moderate · 29 minor.

Open the Cimetidine interaction page

One more smart check

Taking Green Tea as Part of a Dietary Supplement Product? Check It for Interactions

We hold 9,084 real supplement products containing Green Tea, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Green Tea. Your product may carry other ingredients that interact with Cimetidine too, on top of Green Tea — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Green Tea and Cimetidine Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Green Tea
Top 5%

#25 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Cimetidine
Top half

#1,063 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Green Tea

What is Green Tea?

Green Tea
  • Antioxidant support
  • Weight loss
  • Heart health
  • Mental alertness
  • Cancer risk reduction

Green tea is a popular beverage rich in antioxidants called catechins, and drinking it in normal amounts is considered safe for most people. Concentrated green tea extracts are a different story—they may help modestly with weight or heart health for some, but high doses have been linked to rare liver problems. Talk to your pharmacist or doctor before taking green tea supplements, especially if you have liver concerns or are pregnant.

Read the full Green Tea monograph & all interactions
Medication

About Cimetidine

What Is Cimetidine Used For?

Brand names: Tagamet HB, Tagamet, Cimetidine Injection

Cimetidine tablets sold over the counter — including brands like Acid Controller, Acid Reducer, Basic Care Acid Reducer, Equate Cimetidine, and cimetidine 200 — are used to relieve heartburn associated with acid indigestion and sour stomach, and to prevent heartburn brought on by eating or drinking certain foods and beverages.

Prescription-strength cimetidine tablets and Cimetidine Hydrochloride Oral Solution are used for more serious conditions: short-term treatment of active duodenal ulcers (ulcers in the upper small intestine) and benign gastric ulcers (stomach ulcers), maintenance therapy to keep duodenal ulcers from coming back, healing of erosive GERD (acid reflux that has damaged the lining of the esophagus), and treatment of conditions that cause the stomach to make too much acid — such as Zollinger-Ellison Syndrome, systemic mastocytosis, and multiple endocrine adenomas.

See full Cimetidine drug information
Keep checking

Other Drugs & Green Tea

Browse every other medication we’ve checked against Green Tea — both the ones with a known interaction and the ones without. Select any drug for the full detail.

13Major
904Moderate
375Minor
1,537No known interaction
13 Major 904 Moderate 375 Minor 1,537 No interaction
Major

13 interactions

Moderate

904 interactions

Showing 60 of 904 moderate interactions — see all 904 on the Green Tea page.

Minor

375 interactions

Showing 60 of 375 minor interactions — see all 375 on the Green Tea page.

No interaction 1,537 drugs checked — show the list

We also checked Green Tea against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,537 medications checked with no known interaction — see the full Green Tea list.

See the full Green Tea interactions page
See every supplement checked against Cimetidine, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Green Tea monograph › Uses, safety, and every drug interaction in one place Cimetidine supplement interactions › Every supplement checked against Cimetidine, ranked by severity Cimetidine drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Green Tea and Cimetidine Together: Common Questions

Can you take Green Tea with Cimetidine?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 3 interactions listed for Green Tea and Cimetidine?
Cimetidine belongs to more than one drug category, and Green Tea interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Green Tea and Cimetidine interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Cimetidine and Green Tea?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.