Drug & supplement interaction

Comfrey + Clemastine

Clemastine brand name: Tavist Allergy.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Comfrey and Clemastine in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Comfrey and Clemastine

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Clemastine and Comfrey in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Comfrey safety at a glance

Comfrey overall Use caution Topical use on unbroken skin for short periods may be acceptable, but oral use is unsafe due to liver toxicity.
Pregnancy Likely Unsafe When used orally or topically. In addition to hepatotoxicity and possible carcinogenicity, the pyrrolizidine alkaloids (PAs) in comfrey might be teratogenic. PA... Read the full pregnancy detail
Breastfeeding Likely Unsafe When used orally or topically. In addition to hepatotoxicity and possible carcinogenicity, the pyrrolizidine alkaloids (PAs) in comfrey might be teratogenic. PA... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Clemastine and Comfrey? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Clemastine

Interactions in our licensed database are recorded against drug classes, not just single drug names. Clemastine is filed under 4 classifications — including anticholinergic drugs, photosensitizing drugs, seizure threshold lowering drugs. Comfrey has documented interactions with 2 drug classes — the most serious being cytochrome p450 3a4 (cyp3a4) inducers (moderate) and hepatotoxic drugs (moderate) — and none of Clemastine’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Comfrey Does Interact With Other Medications

Comfrey has 438 moderate known drug interactions in our database — Clemastine isn’t one of them. If you take anything else, check it against the full list below.

Moderate 438 No known interaction 2,392 (incl. Clemastine)
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.

What to actually watch for

No Interaction Found — But Data Suggests Comfrey and Clemastine May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • Tiredness / Diarrhea / Vomiting Additional detail

    Comfrey

    “The pyrrolizidine alkaloid constituents of comfrey can cause acute sinusoidal obstruction syndrome characterized by sudden abdominal pain, vomiting, ascites, and hepatomegaly. In subacute disease, comfrey can cause ascites, hepatomegaly, abdominal pain, diarrhea, vomiting, and abdominal swelling. Chronic toxicity appears as asthenia and progressive ascites.”

    Comfrey · Natural Medicines adverse-effect record, reported in cirrhosis.

    2 sources cited
    1. 11988. 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. 11990. Stickel F, Seitz HK. The efficacy and safety of comfrey. Public Health Nutr 2000;3:501-8. PubMed

    Clemastine

    Listed in the ADVERSE REACTIONS section of the FDA label for Clemastine. Read the label on DailyMed ›

  • A skin rash Additional detail

    Comfrey

    “Topically, comfrey-containing creams and ointments may cause skin redness, irritation, itching, rash, and eczema.”

    Comfrey · Natural Medicines adverse-effect record, reported in eczema.

    6 sources cited
    1. 44902. Predel, H. G., Giannetti, B., Koll, R., Bulitta, M., and Staiger, C. Efficacy of a comfrey root extract ointment in comparison to a diclofenac gel in the treatment of ankle distortions: results of an observer-blind, randomized, multicenter study. Phytome
    2. 44912. Giannetti, B. M., Staiger, C., Bulitta, M., and Predel, H. G. Efficacy and safety of comfrey root extract ointment in the treatment of acute upper or lower back pain: results of a double-blind, randomised, placebo controlled, multicentre trial. Br.J Spor PubMed
    3. 44917. Tanret, I. and Duh, D. [Pharmaceutical sheet. Symphytum officinale L., dermal use (Flexagile cream)]. J Pharm.Belg. 2012;(1):41-42.
    4. 44919. Laslett, L. L., Quinn, S. J., Darian-Smith, E., Kwok, M., Fedorova, T., Korner, H., Steels, E., March, L., and Jones, G. Treatment with 4Jointz reduces knee pain over 12 weeks of treatment in patients with clinical knee osteoarthritis: a randomised contr
    5. 92566. Frost R, Macpherson H, O'meara S. A critical scoping review of external uses of comfrey (Symphytum spp.). Complement Ther Med. 2013;21(6):724-45. PubMed
    6. 92570. Pabst H, Schaefer A, Staiger C, Junker-samek M, Predel HG. Combination of comfrey root extract plus methyl nicotinate in patients with conditions of acute upper or low back pain: a multicentre randomised controlled trial. Phytother Res. 2013;27(6):811-7. PubMed

    Clemastine

    Listed in the ADVERSE REACTIONS section of the FDA label for Clemastine. Read the label on DailyMed ›

Reported for Comfrey but not commonly for Clemastine: liver problems, stomach pain, raised blood pressure and swelling.

Effects for Clemastine come from the ADVERSE REACTIONS section of its FDA label; effects for Comfrey come from the Natural Medicines adverse-effect record, quoted above. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Comfrey in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Unsafe

When used orally or topically. In addition to hepatotoxicity and possible carcinogenicity, the pyrrolizidine alkaloids (PAs) in comfrey might be teratogenic. PAs are absorbed through the skin.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

From our Q&A

Questions About Comfrey or Clemastine

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

This page covers Comfrey only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Clemastine page lists 72 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Henbane (major), Scopolia (major), Alfalfa (moderate) and Angel's Trumpet (moderate).

By severity: 3 major · 57 moderate · 12 minor.

From our pharmacist’s overview on the Clemastine page

“Clemastine (Tavist Allergy) is an older, sedating antihistamine that already dries the mouth, blurs vision, and slows the gut, and that is exactly why this list earns real caution rather than a quick skim. Thirty of the 72 supplements on file pile the same drying, sedating anticholinergic load on top, and two of the three major-rated e…”

Reviewed by 2 · Jul 18, 2026

Open the Clemastine 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. Even though Comfrey itself has no known interaction with Clemastine, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Comfrey and Clemastine 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

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

29 days ago today
Medication Clemastine
Steady interest

#1,949 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Comfrey reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Comfrey and Clemastine records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
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.

Symphytum officinale · Boraginaceae · Leaves and roots · Topical ointments, creams, salves, poultices, and (less safely) teas

An interaction check asks whether these two react with each other — it does not ask whether Comfrey is a good idea for someone in your situation. Here is what our Comfrey record says about it on its own.

Comfrey: dosing

There is no well-established, standardized dose for comfrey, and oral use is not recommended at any dose because of liver toxicity.For topical products, follow the directions on the product label and do not use more than directed or for longer than recommended (usually a few weeks at most).

From our Comfrey monograph — the full record covers uses, side effects and every documented interaction.

Read the full Comfrey monograph & all interactions
Medication

About Clemastine

What Is Clemastine Used For?

Brand name: Tavist Allergy

Clemastine treats symptoms of allergic rhinitis (hay fever and similar nasal allergies) — including sneezing, runny nose, itching, and watery eyes. The oral solution (Clemastine Fumarate syrup) is indicated for adults and children aged 6 through 12 years. The tablets (Clemastine Fumarate and Clemsza) are indicated for adults.

Clemastine also treats mild, uncomplicated allergic skin reactions — specifically urticaria (hives) and angioedema (swelling under the skin) — at the appropriate dosage level, in both the oral solution and tablet forms.

See full Clemastine 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
438Moderate
0Minor
2,391No known interaction
438 Moderate 2,391 No interaction
Moderate

438 interactions

Showing 60 of 438 moderate interactions — see all 438 on the Comfrey page.

No interaction 2,391 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 2,391 medications checked with no known interaction — see the full Comfrey list.

See the full Comfrey interactions page
See every supplement checked against Clemastine, ranked by severity
Evidence & sources

Comfrey References

The 13 references that drive our Comfrey monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Stewart MJ, Steenkamp V. Pyrrolizidine poisoning: a neglected area in human toxicology. Ther Drug Monit 2001;23:698-708. PubMed
  2. 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.
  3. Stickel F, Seitz HK. The efficacy and safety of comfrey. Public Health Nutr 2000;3:501-8. PubMed
  4. Chojkier M. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. J Hepatol 2003;39:437-46. PubMed
  5. Wang YP, Yan J, Fu PP, Chou MW. Human liver microsomal reduction of pyrrolizidine alkaloid N-oxides to form the corresponding carcinogenic parent alkaloid. Toxicol Lett 2005;155:411-20. PubMed
  6. Predel, H. G., Giannetti, B., Koll, R., Bulitta, M., and Staiger, C. Efficacy of a comfrey root extract ointment in comparison to a diclofenac gel in the treatment of ankle distortions: results of an observer-blind, randomized, multicenter study. Phytome
  7. Gyorik, S. and Stricker, H. Severe pulmonary hypertension possibly due to pyrrolizidine alkaloids in polyphytotherapy. Swiss.Med.Wkly. 4-4-2009;139(13-14):210-211.
  8. Giannetti, B. M., Staiger, C., Bulitta, M., and Predel, H. G. Efficacy and safety of comfrey root extract ointment in the treatment of acute upper or lower back pain: results of a double-blind, randomised, placebo controlled, multicentre trial. Br.J Spor PubMed
  9. Tanret, I. and Duh, D. [Pharmaceutical sheet. Symphytum officinale L., dermal use (Flexagile cream)]. J Pharm.Belg. 2012;(1):41-42.
  10. Laslett, L. L., Quinn, S. J., Darian-Smith, E., Kwok, M., Fedorova, T., Korner, H., Steels, E., March, L., and Jones, G. Treatment with 4Jointz reduces knee pain over 12 weeks of treatment in patients with clinical knee osteoarthritis: a randomised contr
  11. Frost R, Macpherson H, O'meara S. A critical scoping review of external uses of comfrey (Symphytum spp.). Complement Ther Med. 2013;21(6):724-45. PubMed
  12. Pabst H, Schaefer A, Staiger C, Junker-samek M, Predel HG. Combination of comfrey root extract plus methyl nicotinate in patients with conditions of acute upper or low back pain: a multicentre randomised controlled trial. Phytother Res. 2013;27(6):811-7. PubMed
  13. Smith DB, Jacobson BH. Effect of a blend of comfrey root extract (Symphytum officinale L.) and tannic acid creams in the treatment of osteoarthritis of the knee: randomized, placebo-controlled, double-blind, multiclinical trials. J Chiropr Med. 2011;10(3) PubMed

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Comfrey and Clemastine Together: Common Questions

Is it safe to take Comfrey with Clemastine?
We do not list a known interaction between Comfrey and Clemastine. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do Comfrey and Clemastine have any of the same side effects?
Yes — our sources link each of them separately to 4 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
How was the Comfrey and Clemastine combination checked?
Interactions in our licensed database are recorded against drug classes. Clemastine is filed under 4 classifications, and Comfrey has documented interactions with 2 drug classes — none of Clemastine's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Comfrey interact with any other medications?
Yes. Comfrey has 438 documented drug interactions in our database — Clemastine is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Clemastine interact with any supplements?
Yes. Clemastine has documented interactions with 72 supplements in our database — Comfrey is not one of them. The Clemastine interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

Comfrey monograph Uses, safety profile, and every drug interaction in one place Clemastine drug information The full plain-English guide to this medication Clemastine supplement interactions Every supplement checked against Clemastine, 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 References The 13 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Clemastine 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.