Drug & supplement interaction

Comfrey + Metronidazole, Tetracyline, Bismuth Subcitrate Potassium

Metronidazole, Tetracyline, Bismuth Subcitrate Potassium brand name: Pylera.

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

Comfrey has a moderate interaction with Metronidazole, Tetracyline, Bismuth Subcitrate Potassium. Theoretically, comfrey might have additive adverse effects on the liver when used with hepatotoxic drugs.

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

Comfrey and Metronidazole, Tetracyline, Bismuth Subcitrate Potassium

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

Moderate

HEPATOTOXIC DRUGS

Why this applies to Metronidazole, Tetracyline, Bismuth Subcitrate Potassium

Metronidazole, Tetracyline, Bismuth Subcitrate Potassium falls under HEPATOTOXIC DRUGS — the group Comfrey interacts with.

Theoretically, comfrey might have additive adverse effects on the liver when used with hepatotoxic drugs.
Due to its pyrrolizidine alkaloid constituents, comfrey can cause hepatotoxic effects, including ascites, cirrhosis, hepatic fibrosis, hepatomegaly, and sinusoidal obstruction syndrome.
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 concern with pairing comfrey and Pylera (the bismuth, metronidazole, and tetracycline combo used to clear H. pylori and heal ulcers). Comfrey contains pyrrolizidine alkaloids that can be hard on the liver, especially when swallowed. Both metronidazole and tetracycline can occasionally stress the liver too, so the worry is that stacking them together could add up and increase the chance of liver trouble.

To be honest, this is a theoretical caution based on how these substances behave, not on documented cases with this exact combo, so I don't want to alarm you. Still, comfrey should never be taken by mouth at all. If you're using a topical comfrey product on intact skin, that's far less concerning. Please run it past your pharmacist or doctor first, and tell them right away if you notice yellowing skin or eyes, dark urine, belly pain, or unusual tiredness.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Food and Drug Administration. FDA Advises Dietary Supplement Manufacturers to Remove Comfrey Products From the Market. July 6, 2001. Available at: http://www.cfsan.fda.gov/~dms/dspltr06.html.
  2. Stickel F, Seitz HK. The efficacy and safety of comfrey. Public Health Nutr 2000;3:501-8. 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

Comfrey Also Interacts With Other Medications

Comfrey has 437 moderate known drug interactions in our database — the Metronidazole, Tetracyline, Bismuth Subcitrate Potassium one above is one of them. If you take anything else, check it against the full list below.

Moderate 437 No known interaction 2,393 (incl. Metronidazole, Tetracyline, Bismuth Subcitrate Potassium)
Taking anything else?

Check Another of Your Medications Against Comfrey

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

Everything else you take

See Every Supplement That Interacts With Metronidazole, Tetracyline, Bismuth Subcitrate Potassium

This page covers Comfrey only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metronidazole, Tetracyline, Bismuth Subcitrate Potassium page lists 148 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Beer (major), Oleander (major) and Siberian Cocklebur (major).

By severity: 6 major · 128 moderate · 14 minor.

From our pharmacist’s overview on the Metronidazole, Tetracyline, Bismuth Subcitrate Potassium page

“Alcohol is the risk to handle first with Pylera (metronidazole, tetracycline, and bismuth subcitrate potassium, usually prescribed for H. pylori stomach infections).”

Reviewed by 2 · Jul 18, 2026

Open the Metronidazole, Tetracyline, Bismuth Subcitrate Potassium interaction page

One more smart check

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

We hold 29 real supplement products containing Comfrey, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Comfrey. Your product may carry other ingredients that interact with Metronidazole, Tetracyline, Bismuth Subcitrate Potassium too, on top of Comfrey — 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 Comfrey and Metronidazole, Tetracyline, Bismuth Subcitrate Potassium 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 Comfrey
Top half

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

29 days ago today
Medication Metronidazole, Tetracyline, Bismuth Subcitrate Potassium
Steady interest

#2,174 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 Comfrey

What is Comfrey?

Comfrey
  • Bruises and sprains
  • Muscle and joint pain
  • Minor wounds and skin irritation
  • Back pain
  • Inflammation

Comfrey is a traditional herb used mainly on the skin for bruises, sprains, and joint pain, and some topical products show modest benefit for these uses. However, comfrey contains compounds that can seriously damage the liver, so it should never be taken by mouth and should only be used on unbroken skin for short periods. Pregnant or breastfeeding people should avoid it entirely.

Read the full Comfrey monograph & all interactions
Medication

About Bismuth, Metronidazole, and Tetracycline

What Is Bismuth, Metronidazole, and Tetracycline Used For?

Brand name: Pylera

This combination — bismuth subcitrate potassium, metronidazole, and tetracycline hydrochloride — is used to eradicate Helicobacter pylori (H. pylori), the bacterial infection linked to duodenal ulcers. It is always taken alongside omeprazole as part of a complete treatment regimen. Getting rid of H. pylori has been shown to reduce the risk of duodenal ulcers coming back.

It is approved for adults who have an active duodenal ulcer or a history of one within the past five years. Like all antibiotics, it should only be used for infections that are proven or strongly suspected to be caused by bacteria, to help prevent antibiotic resistance.

See full Bismuth, Metronidazole, and Tetracycline drug information
Keep checking

Other Drugs & Comfrey

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

0Major
437Moderate
0Minor
2,392No known interaction
437 Moderate 2,392 No interaction
Moderate

437 interactions

Showing 60 of 437 moderate interactions — see all 437 on the Comfrey page.

No interaction 2,392 drugs checked — show the list

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

Showing the 60 most looked-up of 2,392 medications checked with no known interaction — see the full Comfrey list.

See the full Comfrey interactions page
See every supplement checked against Metronidazole, Tetracyline, Bismuth Subcitrate Potassium, 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
Comfrey monograph › Uses, safety, and every drug interaction in one place Metronidazole, Tetracyline, Bismuth Subcitrate Potassium supplement interactions › Every supplement checked against Metronidazole, Tetracyline, Bismuth Subcitrate Potassium, ranked by severity Bismuth, Metronidazole, and Tetracycline 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 Comfrey and Metronidazole, Tetracyline, Bismuth Subcitrate Potassium Together: Common Questions

Can you take Comfrey with Metronidazole, Tetracyline, Bismuth Subcitrate Potassium?
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 Comfrey and Metronidazole, Tetracyline, Bismuth Subcitrate Potassium 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 Metronidazole, Tetracyline, Bismuth Subcitrate Potassium and Comfrey?

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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.