Drug & supplement interaction

Green Tea + Terfenadine

Terfenadine brand name: Seldane.

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

Green Tea has a moderate interaction with Terfenadine. Green tea might increase the levels and adverse effects of P-glycoprotein (P-gp) substrates.

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

Green Tea and Terfenadine

Here is the interaction we found between these two, with the evidence behind it.

Moderate

P-GLYCOPROTEIN SUBSTRATES

Why this applies to Terfenadine

Terfenadine falls under P-GLYCOPROTEIN SUBSTRATES — the group Green Tea interacts with.

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 gist for terfenadine (older brand Seldane): your body uses a pump called P-glycoprotein to help shuttle this drug out and keep its blood levels in check. Green tea may slow that pump down a bit, which could let more terfenadine build up in your system than expected.

That matters because terfenadine is one of those drugs where higher levels can affect the heart's rhythm (a problem called QT prolongation). That's actually why this drug was pulled from the U.S. market years ago. The evidence here is thin, just lab studies and a few case reports, so plain cups of tea are unlikely to be a big deal. Still, if you're taking terfenadine, please check in with your pharmacist or doctor before adding concentrated green tea supplements.

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

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 Terfenadine one above is one of 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. Terfenadine)
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 Terfenadine

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 Terfenadine, 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 Terfenadine

This page covers Green Tea only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Terfenadine page lists 65 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), Arsenic (major), Cesium (major) and Ephedra (major).

By severity: 8 major · 42 moderate · 15 minor.

From our pharmacist’s overview on the Terfenadine page

“Terfenadine (Seldane) is an older antihistamine with a well-known heart rhythm hazard, and its supplement list warrants genuine caution. Eight of the 65 interactions on file are rated major, and the biggest danger is additive strain on the heart's electrical timing: 13 ingredients can prolong the QT interval the way terfenadine itself…”

Reviewed by 2 · Jul 18, 2026

Open the Terfenadine 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 Terfenadine 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 Terfenadine 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%

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

29 days ago today
Medication Terfenadine
Steady interest

#2,680 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
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 Terfenadine, 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 Terfenadine supplement interactions › Every supplement checked against Terfenadine, ranked by severity 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 Terfenadine Together: Common Questions

Can you take Green Tea with Terfenadine?
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.
How serious is the Green Tea and Terfenadine 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 Terfenadine 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.