Drug & supplement interaction

Ilex Guayusa + Metformin

Metformin brand names: Glucophage, Metformin.

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

Metformin falls into 2 drug categories that Ilex Guayusa can interact with; the most serious is rated minor. Theoretically, taking Ilex guayusa with antidiabetes drugs might increase the risk of hypoglycemia.

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

Ilex Guayusa and Metformin

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

Why Are There 2 Interactions?

Ilex Guayusa interacts with whole categories of medication. Metformin falls into 2 of those categories, so it can interact with Ilex Guayusa 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

Metformin falls under ANTIDIABETES DRUGS — the group Ilex Guayusa interacts with.

Theoretically, taking Ilex guayusa with antidiabetes drugs might increase the risk of hypoglycemia.
Animal research in a model of hyperglycemia suggests that Ilex guayusa may have antihyperglycemic effects, although it does not appear to lower glucose levels when compared with baseline. This effect has not been evaluated 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 gist if you enjoy guayusa tea and take metformin for your type 2 diabetes. There's a thought on paper that guayusa might nudge your blood sugar a little lower, which could add to what metformin is already doing. If that happened, you might notice signs of low blood sugar like shakiness, sweating, dizziness, or feeling hungry and irritable.

The honest truth is that this is very weak evidence. It comes from animal studies, and in those studies guayusa didn't actually drop sugar below normal levels. It has never been tested in people this way, so I'd call the real-world risk small. Still, if you start drinking it regularly, it's smart to keep an eye on your readings and mention it to your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Swanston-Flatt SK, Day C, Flatt PR, Gould BJ, Bailey CJ. Glycaemic effects of traditional European plant treatments for diabetes. Studies in normal and streptozotocin diabetic mice. Diabetes Res 1989;10(2):69-73.
  2. Mello TC, Dias DDS, Bernardes N, et al. Ilex Guayusa Tea Improves Glycaemia and Autonomic Modulation in Female Streptozotocin-Induced Diabetic Rats. Pharmaceuticals (Basel) 2025;18(3):316. PubMed
Minor

METFORMIN (Glucophage)

2 of 2
Theoretically, metformin might increase the levels and adverse effects of caffeine.
Ilex guayusa 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 the interesting twist with this pair: it's not your metformin that gets affected, it's the caffeine in the guayusa tea. Animal studies hint that metformin may slow down how your body clears caffeine, so the caffeine could hang around a bit longer than usual. That might mean you feel the effects of a cup more strongly, things like jitteriness, a racing heart, trouble sleeping, or feeling wired.

I want to be honest though: this is only based on lab and animal research, so it's more of a theoretical heads-up than a proven problem. Your blood sugar control from metformin shouldn't change. If you notice caffeine hitting you harder than normal, just ease back on the guayusa 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

Ilex Guayusa Also Interacts With Other Medications

Ilex Guayusa has 8 major, 470 moderate, 126 minor known drug interactions in our database — the Metformin one above is among them. If you take anything else, check it against the full list below.

Major 8 Moderate 470 Minor 126 No known interaction 2,226 (incl. Metformin)
Taking anything else?

Check Another of Your Medications Against Ilex Guayusa

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

From our Q&A

Questions About Ilex Guayusa or Metformin

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Ilex Guayusa or Metformin, 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

This page covers Ilex Guayusa only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metformin page lists 258 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 · 39 minor.

From our pharmacist’s overview on the Metformin page

“Siberian cocklebur is the ingredient I most want anyone taking metformin (Glucophage) to know about. It has caused severe low blood sugar in people, documented in humans, and it should not be combined with any glucose-lowering medication.”

Reviewed by 2 · Jul 18, 2026

Open the Metformin interaction page

How much people look this up

Where Ilex Guayusa and Metformin 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 Ilex Guayusa
Steady interest

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

29 days ago today
Medication Metformin
Top 1%

#28 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 Ilex Guayusa

What is Ilex Guayusa?

  • Energy and alertness
  • Mental focus
  • Antioxidant support
  • Appetite control
  • Athletic and physical performance

Ilex guayusa is a caffeine-containing holly leaf from the Amazon, traditionally brewed as a tea for energy and alertness, much like yerba mate or green tea. There is limited human research confirming specific health benefits, and its main reliable effect comes from its caffeine content. Because it is a stimulant, use it cautiously and check with your pharmacist or doctor if you have heart concerns or are pregnant.

Read the full Ilex Guayusa monograph & all interactions
Medication

About Metformin

What Is Metformin Used For?

Brand names: Glucophage, Metformin

Metformin — available as tablets, extended-release tablets, and an oral solution — is used to improve blood sugar (glucose) control in people with type 2 diabetes mellitus, always as part of a plan that includes diet and exercise.

Metformin hydrochloride tablets and the oral solution are approved for adults and children 10 years and older. Extended-release tablets (including Fortamet, Glumetza, and Metformin Hydrochloride Extended Release) are approved for adults only. Riomet (oral solution) is approved for adults and children 10 years and older.

See full Metformin drug information
Keep checking

Other Drugs & Ilex Guayusa

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

8Major
470Moderate
126Minor
2,225No known interaction
8 Major 470 Moderate 126 Minor 2,225 No interaction
Major

8 interactions

Moderate

470 interactions

Showing 60 of 470 moderate interactions — see all 470 on the Ilex Guayusa page.

Minor

126 interactions

Showing 60 of 126 minor interactions — see all 126 on the Ilex Guayusa page.

No interaction 2,225 drugs checked — show the list

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

Showing the 60 most looked-up of 2,225 medications checked with no known interaction — see the full Ilex Guayusa list.

See the full Ilex Guayusa interactions page
See every supplement checked against Metformin, 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
Ilex Guayusa monograph › Uses, safety, and every drug interaction in one place Metformin supplement interactions › Every supplement checked against Metformin, ranked by severity Metformin 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 Ilex Guayusa and Metformin Together: Common Questions

Can you take Ilex Guayusa with Metformin?
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 Ilex Guayusa and Metformin?
Metformin belongs to more than one drug category, and Ilex Guayusa 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 Ilex Guayusa and Metformin 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 and Ilex Guayusa?

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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.