Drug & supplement interaction

White Horehound + Metformin Hydrochloride

Metformin Hydrochloride brand name: Riomet ER.

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

White Horehound has a moderate interaction with Metformin Hydrochloride. Evidence from animal research suggests that white horehound might lower blood glucose.

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

White Horehound and Metformin Hydrochloride

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

Moderate

ANTIDIABETES DRUGS

Why this applies to Metformin Hydrochloride

Metformin Hydrochloride falls under ANTIDIABETES DRUGS — the group White Horehound interacts with.

Evidence from animal research suggests that white horehound might lower blood glucose. However, preliminary clinical research suggests that white horehound only slightly lowers blood glucose when taken in combination with antidiabetic agents, suggesting that the effect may not be clinically significant. Until more is known, use with caution. Theoretically, white horehound may have additive effects when used by patients taking antidiabetic drugs. The dose of diabetes medications might need to be adjusted. Some antidiabetes drugs include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, metformin (Glucophage), pioglitazone (Actos), rosiglitazone (Avandia), and others.
Severity Moderate Likelihood Possible Evidence B

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 with white horehound and your metformin: this herb may have a mild blood sugar lowering effect of its own. When you stack that on top of metformin, the two could add up and nudge your glucose lower than metformin alone would. In theory, that raises the chance of low blood sugar symptoms like shakiness, sweating, dizziness, or feeling unusually tired, though metformin by itself rarely causes serious lows.

The honest truth is the evidence here is thin. Animal studies hinted at a sugar lowering effect, but early human research suggests any extra drop is small and may not really matter day to day. An occasional white horehound cough drop is very unlikely to be a problem. If you plan to use concentrated supplement doses regularly, mention it to your pharmacist or doctor first and keep an eye on your home glucose readings.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Roman, Ramos R., Alarcon-Aguilar, F., Lara-Lemus, A., and Flores-Saenz, J. L. Hypoglycemic effect of plants used in Mexico as antidiabetics. Arch.Med.Res 1992;23:59-64.
  2. Novaes AP, Rossi C, Poffo C, et al. Preliminary evaluation of the hypoglycemic effect of some Brazilian medicinal plants. Therapie. 2001;56(4):427-30.
  3. Herrera-Arellano, A., Aguilar-Santamaria, L., Garcia-Hernandez, B., Nicasio-Torres, P., and Tortoriello, J. Clinical trial of Cecropia obtusifolia and Marrubium vulgare leaf extracts on blood glucose and serum lipids in type 2 diabetics. Phytomedicine 200 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

White Horehound Also Interacts With Other Medications

White Horehound has 257 moderate known drug interactions in our database — the Metformin Hydrochloride one above is one of them. If you take anything else, check it against the full list below.

Moderate 257 No known interaction 2,573 (incl. Metformin Hydrochloride)
Taking anything else?

Check Another of Your Medications Against White Horehound

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

Everything else you take

See Every Supplement That Interacts With Metformin Hydrochloride

This page covers White Horehound 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

How much people look this up

Where White Horehound 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 White Horehound
Steady interest

#1,036 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Metformin Hydrochloride
Top 10%

#159 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 White Horehound

What is White Horehound?

White Horehound
  • Cough and chest congestion
  • Sore throat
  • Bronchitis
  • Digestive upset and poor appetite
  • Bloating and gas

White horehound is a traditional bitter herb used mainly for coughs, sore throats, and mild digestive complaints, and it is a common flavoring in old-fashioned cough drops. Solid human evidence supporting these uses is limited, so view it as a folk remedy rather than a proven treatment. Talk to your pharmacist or doctor before using it, and avoid it during pregnancy.

Read the full White Horehound monograph & all interactions
Keep checking

Other Drugs & White Horehound

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

0Major
257Moderate
0Minor
2,572No known interaction
257 Moderate 2,572 No interaction
Moderate

257 interactions

Showing 60 of 257 moderate interactions — see all 257 on the White Horehound page.

No interaction 2,572 drugs checked — show the list

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

Showing the 60 most looked-up of 2,572 medications checked with no known interaction — see the full White Horehound list.

See the full White Horehound 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
White Horehound 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 White Horehound and Metformin Hydrochloride Together: Common Questions

Can you take White Horehound with Metformin Hydrochloride?
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 White Horehound and Metformin Hydrochloride 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 Metformin Hydrochloride and White Horehound?

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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.