Drug & supplement interaction

Green Tea + Conjugated Estrogens

Conjugated Estrogens brand names: Premarin, Cenestin, Enjuvia, Premarin Vaginal Cream.

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

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

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

Green Tea and Conjugated Estrogens

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. Conjugated Estrogens 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

ESTROGENS

1 of 3

Why this applies to Conjugated Estrogens

Conjugated Estrogens falls under ESTROGENS — the group Green Tea interacts with.

Theoretically, estrogens might increase the levels and adverse effects of caffeine.
Green tea contains caffeine. Estrogen inhibits caffeine metabolism.
Severity Moderate Likelihood Probable Evidence B

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..

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

Here's a twist worth knowing: in this pairing, it's actually your estrogen that affects the green tea, not the other way around. Conjugated estrogens like Premarin can slow down how your body clears caffeine, and green tea naturally contains caffeine. So if you're taking estrogen, the caffeine from your green tea can linger longer and hit a little harder than usual.

In real life, that might mean more jitteriness, a racing or pounding heart, trouble sleeping, or feeling restless after your usual cup. A normal mug or two of green tea is rarely a big deal for most people, but concentrated green tea extract pills or lots of cups could add up. If caffeine seems to bother you more since starting estrogen, just mention it to your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Pollock BG, Wylie M, Stack JA, et al. Inhibition of caffeine metabolism by estrogen replacement therapy in postmenopausal women. J Clin Pharmacol 1999;39:936-40. PubMed
Moderate

P-GLYCOPROTEIN SUBSTRATES

2 of 3

Conjugated Estrogens 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 gist for Premarin and other conjugated estrogens: green tea may gently block a cellular pump called P-glycoprotein that helps move some medicines out of your body. If that pump slows down, a bit more estrogen could stay in your system. In theory, that might nudge up familiar estrogen side effects like breast tenderness, bloating, nausea, headaches, or spotting.

I want to keep this in perspective, though. This is based on lab studies and a few scattered case reports, so the evidence is pretty thin, and a cup or two of green tea is unlikely to cause trouble for most people. Concentrated green tea extract capsules are where I'd be more cautious. If you take those regularly, just run it by your pharmacist or doctor 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
Minor

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

3 of 3

Conjugated Estrogens also falls under CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES.

Green tea is unlikely to produce clinically significant changes in the levels and clinical effects of CYP3A4 substrates.
In vitro and in vivo research suggests that green tea can inhibit intestinal CYP3A and induce hepatic CYP3A4 enzymes. However, this effect is unlikely to be clinically significant, as green tea does not appear to affect CYP3A4 activity in humans.
Severity Minor Likelihood Unlikely Evidence D

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

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

Here's the short version: your body uses a liver enzyme called CYP3A4 to help process conjugated estrogens (Premarin), and green tea has shown some mixed effects on that enzyme in lab and animal studies. In test tubes it looked like green tea might slow this enzyme in the gut while nudging it up in the liver. On paper, that could shift estrogen levels slightly, in theory changing how strong the effects are or how often you notice side effects like breast tenderness, nausea, headaches, or bloating.

The reassuring part is that in actual human studies, green tea doesn't appear to meaningfully change CYP3A4 activity. So drinking your usual cups of tea is very unlikely to cause a problem. If you're considering concentrated green tea extract pills, just give your pharmacist or doctor a heads-up first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Donovan JL, Chavin KD, Devane CL, et al. Green tea (Camellia sinensis) extract does not alter cytochrome P450 3A4 or 2D6 activity in healthy volunteers. Drug Metab Dispos 2004;32:906-8. PubMed
  2. Nishikawa, M., Ariyoshi, N., Kotani, A., Ishii, I., Nakamura, H., Nakasa, H., Ida, M., Nakamura, H., Kimura, N., Kimura, M., Hasegawa, A., Kusu, F., Ohmori, S., Nakazawa, K., and Kitada, M. Effects of continuous ingestion of green tea or grape seed extrac
  3. Chow, H. H., Hakim, I. A., Vining, D. R., Crowell, J. A., Cordova, C. A., Chew, W. M., Xu, M. J., Hsu, C. H., Ranger-Moore, J., and Alberts, D. S. Effects of repeated green tea catechin administration on human cytochrome P450 activity. Cancer Epidemiol.B PubMed
  4. Engdal, S. and Nilsen, O. G. In vitro inhibition of CYP3A4 by herbal remedies frequently used by cancer patients. Phytother.Res. 2009;23(7):906-912.
  5. Schönthal AH. Adverse effects of concentrated green tea extracts. Mol Nutr Food Res. 2011 Jun;55(6):874-85. 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 Conjugated Estrogens 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. Conjugated Estrogens)
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 Conjugated Estrogens

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 Conjugated Estrogens, 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 Conjugated Estrogens

This page covers Green Tea only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Conjugated Estrogens page lists 207 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), Tiratricol (major) and Acacia Rigidula (moderate).

By severity: 4 major · 172 moderate · 31 minor.

From our pharmacist’s overview on the Conjugated Estrogens page

“Conjugated estrogens (Premarin, Cenestin) are hormone replacement, most often for menopause symptoms, and the 207 supplements here warrant real care before adding any of them. Most of the risk runs through drug processing: 121 entries involve the CYP3A4 enzyme that clears estrogen, which is how St.”

Reviewed by 2 · Jul 18, 2026

Open the Conjugated Estrogens 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 Conjugated Estrogens 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 Conjugated Estrogens 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%

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

29 days ago today
Medication Conjugated Estrogens
Steady interest

#1,461 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 Conjugated Estrogens, 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 Conjugated Estrogens supplement interactions › Every supplement checked against Conjugated Estrogens, 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 Conjugated Estrogens Together: Common Questions

Can you take Green Tea with Conjugated Estrogens?
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 Conjugated Estrogens?
Conjugated Estrogens 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 Conjugated Estrogens 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 Conjugated Estrogens 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.