Drug & supplement interaction

Black Tea + Metformin, Rosiglitazone

Metformin, Rosiglitazone brand name: Avandamet.

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

Metformin, Rosiglitazone falls into 2 drug categories that Black Tea can interact with; the most serious is rated minor. Theoretically, taking black 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

Black Tea and Metformin, Rosiglitazone

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

Why Are There 2 Interactions?

Black Tea interacts with whole categories of medication. Metformin, Rosiglitazone falls into 2 of those categories, so it can interact with Black 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, Rosiglitazone

Metformin, Rosiglitazone falls under ANTIDIABETES DRUGS — the group Black Tea interacts with.

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.
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

Avandamet combines metformin and rosiglitazone, two medicines that work to lower your blood sugar. The concern with black tea here is really about the caffeine and tea compounds nudging your blood sugar in either direction, not about tea blocking or speeding up how your body clears the medicine. Honestly, this is a minor and mostly theoretical interaction, and the evidence is mixed and on the weaker side.

For most people, enjoying a cup or two of black tea alongside Avandamet won't cause a problem. If you tend to drink large amounts daily, just keep an eye out for unusual swings, like feeling shaky, sweaty, or lightheaded (low sugar) or extra thirst and fatigue. When in doubt, check your readings and chat with your pharmacist or doctor.

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. Bahorun T, Luximon-Ramma A, Neergheen-Bhujun VS, Gunness TK, Googoolye K, Auger C, Crozier A, Aruoma OI. The effect of black tea on risk factors of cardiovascular disease in a normal population. Prev Med. 2012 ;54 Suppl:S98-102. PubMed
Minor

Metformin (Glucophage)

2 of 2
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.
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 something interesting about this combo. It's actually the metformin part of Avandamet that may slow down how your body clears the caffeine in black tea, not the other way around. So instead of the medicine being affected, it's the caffeine that can hang around a little longer and pile up. That could mean more of the usual caffeine effects: feeling jittery, a faster or pounding heartbeat, trouble sleeping, or a bit of stomach upset.

The good news? This is very mild and only shown in lab and animal studies, so I wouldn't lose sleep over it (pun intended). A normal cup or two of tea is unlikely to cause problems for most people. If you notice you feel more wired than usual, just ease back on the caffeine and 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

Black Tea Also Interacts With Other Medications

Black Tea has 8 major, 572 moderate, 113 minor known drug interactions in our database — the Metformin, Rosiglitazone one above is among them. If you take anything else, check it against the full list below.

Major 8 Moderate 572 Minor 113 No known interaction 2,137 (incl. Metformin, Rosiglitazone)
Taking anything else?

Check Another of Your Medications Against Black Tea

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

Everything else you take

See Every Supplement That Interacts With Metformin, Rosiglitazone

This page covers Black Tea only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metformin, Rosiglitazone page lists 315 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Beer (major), Siberian Cocklebur (major), Wine (major) and Acai (moderate).

By severity: 4 major · 268 moderate · 43 minor.

From our pharmacist’s overview on the Metformin, Rosiglitazone page

“Avandamet pairs metformin with rosiglitazone to manage type 2 diabetes, and its supplement list calls for genuine care rather than a quick skim. Start with the four major-rated entries: alcohol and the herb Siberian cocklebur can each stress the liver, a serious concern with rosiglitazone on board, while activated charcoal can soak up…”

Reviewed by 2 · Jul 18, 2026

Open the Metformin, Rosiglitazone interaction page

One more smart check

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

We hold 271 real supplement products containing Black Tea, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Black Tea. Your product may carry other ingredients that interact with Metformin, Rosiglitazone too, on top of Black 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 Black Tea and Metformin, Rosiglitazone 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 Black Tea
Top 25%

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

29 days ago today
Medication Metformin, Rosiglitazone
Steady interest

#1,739 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 Black Tea

What is Black Tea?

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

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.

Read the full Black Tea monograph & all interactions
Keep checking

Other Drugs & Black Tea

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

8Major
572Moderate
113Minor
2,136No known interaction
8 Major 572 Moderate 113 Minor 2,136 No interaction
Major

8 interactions

Moderate

572 interactions

Showing 60 of 572 moderate interactions — see all 572 on the Black Tea page.

Minor

113 interactions

Showing 60 of 113 minor interactions — see all 113 on the Black Tea page.

No interaction 2,136 drugs checked — show the list

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

Showing the 60 most looked-up of 2,136 medications checked with no known interaction — see the full Black Tea list.

See the full Black Tea interactions page
See every supplement checked against Metformin, Rosiglitazone, 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
Black Tea monograph › Uses, safety, and every drug interaction in one place Metformin, Rosiglitazone supplement interactions › Every supplement checked against Metformin, Rosiglitazone, 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 Black Tea and Metformin, Rosiglitazone Together: Common Questions

Can you take Black Tea with Metformin, Rosiglitazone?
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 Black Tea and Metformin, Rosiglitazone?
Metformin, Rosiglitazone belongs to more than one drug category, and Black 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 Black Tea and Metformin, Rosiglitazone 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, Rosiglitazone and Black 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.