Drug & supplement interaction

Green Tea + Metformin Hydrochloride

Metformin Hydrochloride brand name: Riomet ER.

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

Metformin Hydrochloride falls into 2 drug categories that Green Tea can interact with; the most serious is rated minor. Theoretically, taking green tea with antidiabetes drugs might interfere with blood glucose control.

Read the full interaction report
SeverityMinor
LikelihoodUnlikely
Interactions2
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

Green Tea and Metformin Hydrochloride

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

Green Tea interacts with whole categories of medication. Metformin Hydrochloride falls into 2 of those categories, so it can interact with Green Tea in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Minor).

Minor

ANTIDIABETES DRUGS

1 of 2

Why this applies to Metformin Hydrochloride

Metformin Hydrochloride falls under ANTIDIABETES DRUGS — the group Green Tea interacts with.

Theoretically, taking green tea with antidiabetes drugs might interfere with blood glucose control.
Concomitant use of green tea and antidiabetes drugs might interfere with blood glucose control. The data are conflicting. Reports claim that green tea and/or caffeine, a constituent of green tea, might increase or decrease blood sugar.
Severity Minor Likelihood Unlikely Evidence B

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 honest picture: green tea and metformin don't have a strong, well-proven clash. Metformin isn't a prodrug, and green tea doesn't really change how your body activates or clears it. What we have is mostly theoretical, and the studies actually point in both directions. Green tea (and the caffeine in it) might nudge your blood sugar a little up or a little down, which could blunt or slightly boost the effect you get from your metformin.

For most people sipping a normal cup or two a day, this is unlikely to cause real trouble. Concentrated green tea extract pills are where I'd be more cautious, since they pack a much bigger dose. If you notice shakiness, sweating, or unusually high readings, check with your pharmacist or doctor before changing anything.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Watson JM, Jenkins EJ, Hamilton P, et al. Influence of caffeine on the frequency and perception of hypoglycemia in free-living patients with type 1 diabetes. Diabetes Care 2000;23:455-9. PubMed
  2. Bell DG, Jacobs I, Ellerington K. Effect of caffeine and ephedrine ingestion on anaerobic exercise performance. Med Sci Sports Exerc 2001;33:1399-403. PubMed
  3. Josic, J., Olsson, A. T., Wickeberg, J., Lindstedt, S., and Hlebowicz, J. Does green tea affect postprandial glucose, insulin and satiety in healthy subjects: a randomized controlled trial. Nutr.J. 2010;9:63. PubMed
  4. Hsu, C. H., Liao, Y. L., Lin, S. C., Tsai, T. H., Huang, C. J., and Chou, P. Does supplementation with green tea extract improve insulin resistance in obese type 2 diabetics? A randomized, double-blind, and placebo-controlled clinical trial. Altern.Med.R
  5. Bogdanski, P., Suliburska, J., Szulinska, M., Stepien, M., Pupek-Musialik, D., and Jablecka, A. Green tea extract reduces blood pressure, inflammatory biomarkers, and oxidative stress and improves parameters associated with insulin resistance in obese, h
  6. Liu K, Zhou R, Wang B, Chen K, Shi LY, Zhu JD, Mi MT. Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials. Am J Clin Nutr. 2013 Aug;98(2):340-8. PubMed
Minor

METFORMIN (Glucophage)

2 of 2
Theoretically, metformin might increase the levels and adverse effects of caffeine.
Green 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.
Severity Minor 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 a twist on how this one works. It isn't that green tea changes your metformin. Instead, the thinking goes the other way: metformin might slow down how your body clears the caffeine that's naturally in green tea. So the caffeine could hang around a bit longer than usual.

In plain terms, you might feel more of the usual caffeine effects, like jitteriness, a racing heart, trouble sleeping, or a bit of an upset stomach. The good news is this is only a theoretical concern based on animal research, not strong human evidence, and it's rated minor. A normal cup or two of green tea is very unlikely to cause trouble. Concentrated extracts or lots of caffeine are where I'd be more cautious. If you notice you feel wired, mention it to your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Mohiuddin, M., Azam, A. T., Amran, M. S., and Hossain, M. A. In vive effects of gliclazide and metformin on the plasma concentration of caffeine in healthy rats. Pak.J Biol Sci 5-1-2009;12(9):734-737.

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, 905 moderate, 374 minor known drug interactions in our database — the Metformin Hydrochloride one above is among them. If you take anything else, check it against the full list below.

Major 13 Moderate 905 Minor 374 No known interaction 1,538 (incl. Metformin Hydrochloride)
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 Metformin Hydrochloride

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 Metformin Hydrochloride, 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 Metformin Hydrochloride

This page covers Green Tea only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metformin Hydrochloride page lists 257 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Siberian Cocklebur (major), Acai (moderate), African Wild Potato (moderate) and Agaricus Mushroom (moderate).

By severity: 2 major · 217 moderate · 38 minor.

From our pharmacist’s overview on the Metformin Hydrochloride page

“Anyone taking metformin hydrochloride (Riomet ER) should treat this list with genuine care, because two of its 257 entries are rated major. Siberian cocklebur has caused severe hypoglycemia in people and should not be combined with metformin at all, and activated charcoal can adsorb the drug in the gut so less reaches your blood.”

Reviewed by 2 · Jul 18, 2026

Open the Metformin Hydrochloride 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 Metformin Hydrochloride 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 Metformin Hydrochloride 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 Metformin Hydrochloride
Top 10%

#150 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
905Moderate
374Minor
1,537No known interaction
13 Major 905 Moderate 374 Minor 1,537 No interaction
Major

13 interactions

Moderate

905 interactions

Showing 60 of 905 moderate interactions — see all 905 on the Green Tea page.

Minor

374 interactions

Showing 60 of 374 minor interactions — see all 374 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 Metformin Hydrochloride, 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 Metformin Hydrochloride supplement interactions › Every supplement checked against Metformin Hydrochloride, 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 Metformin Hydrochloride Together: Common Questions

Can you take Green Tea with Metformin Hydrochloride?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 2 interactions listed for Green Tea and Metformin Hydrochloride?
Metformin Hydrochloride 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 Metformin Hydrochloride interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

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

Still Have a Question About Metformin Hydrochloride 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.