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Comfrey
Comfrey — what the European monograph actually supports, what it is not for, the form and how long it is meant to be used, side effects, and the 1 medicine interaction documented for it.
This is a reference page, not a diagnosis and not a prescription. Herbal products are real pharmacology: they have effects, side effects and interactions with medicines. Tell your doctor and your pharmacist everything you take, including teas and supplements, and never stop or change a prescribed medicine because of anything you read here.
What it is
Symphytum officinale L. — root and leaf
Local names across the region this site serves: varemerohi (ET) · rohtoraunioyrtti (FI) · окопник (RU).
Grouped here under Where the harm is. Regulatory position: External use only, with limits; oral preparations are not acceptable in the EU.
What the evidence supports
The registered indication: External use on unbroken skin for bruises, sprains and strains, in pyrrolizidine-alkaloid-depleted preparations.
Comfrey is the clearest case of a traditional remedy that modern chemistry ruled out for internal use. It contains pyrrolizidine alkaloids, which the liver converts into reactive compounds that damage the small hepatic veins and cause hepatic veno-occlusive disease (sinusoidal obstruction syndrome); they are also genotoxic and carcinogenic in animal studies. Oral comfrey preparations were withdrawn in Europe decades ago on that basis. Externally, comfrey creams and ointments for bruises and sprains remain in use and have reasonable trial support for pain relief, but regulators restrict them to alkaloid-depleted preparations, intact skin only, and a limited number of days of use per year — because pyrrolizidine alkaloids are absorbed through skin. The wider lesson is that this is not a comfrey-only problem: the same alkaloids occur in ragwort, borage, butterbur and coltsfoot, and they contaminate herbal teas and honey when alkaloid-containing weeds are harvested with the crop. European food law sets maximum levels for pyrrolizidine alkaloids in herbal teas, teas, certain herbs and food supplements for exactly that reason.
D — Popular claim unsupported, or safety dominates The better trials are negative, or the substance appears in the literature mainly for the harm it has caused.
What it is not for
Swallowing, in any form, including comfrey tea and "knitbone" infusions. Also not for open wounds, broken skin or grazes.
Form, strength and how long
Creams, ointments and gels of alkaloid-depleted root or leaf extract, for external use on unbroken skin.
Duration. Limited courses, and a limited total number of days per year — the restriction is on cumulative exposure, not on any single application.
No gram figure appears on this page on purpose. The plant part, the extraction solvent and the drug-to-extract ratio together define a preparation, and a number taken from one does not describe another. The reasoning is set out on the hub; the amount that applies to you is the one printed on the pack you are holding, and a pharmacist will read it with you.
Side effects
Externally, occasional skin irritation and contact allergy. Internally, liver injury that can be severe and irreversible.
Who should avoid it
Never in pregnancy or while breastfeeding. Not on children. Not with existing liver disease.
Interactions with medicines
| Medicine or substance | What is described |
|---|---|
| Anything else that stresses the liver | Anything else that burdens the liver — alcohol, other pyrrolizidine-containing plants, medicines with a hepatic signal — adds to the same target organ. |
The reverse view — start from the medicine rather than the plant — is in the medicine, food and alcohol interactions reference, and summarised for every herb on this site.
Sources: European Medicines Agency — Committee on Herbal Medicinal Products (HMPC), European Union herbal monographs · LiverTox: Clinical and Research Information on Drug-Induced Liver Injury (NIDDK, National Institutes of Health) · checked 2026-09-06
Frequently asked questions
What is comfrey used for?
External use on unbroken skin for bruises, sprains and strains, in pyrrolizidine-alkaloid-depleted preparations. Comfrey is the clearest case of a traditional remedy that modern chemistry ruled out for internal use. It contains pyrrolizidine alkaloids, which the liver converts into reactive compounds that damage the small hepatic veins and cause hepatic veno-occlusive disease (sinusoidal obstruction syndrome); they are also genotoxic and carcinogenic in animal studies. Oral comfrey preparations were withdrawn in Europe decades ago on that basis. Externally, comfrey creams and ointments for bruises and sprains remain in use and have reasonable trial support for pain relief, but regulators restrict them to alkaloid-depleted preparations, intact skin only, and a limited number of days of use per year — because pyrrolizidine alkaloids are absorbed through skin. The wider lesson is that this is not a comfrey-only problem: the same alkaloids occur in ragwort, borage, butterbur and coltsfoot, and they contaminate herbal teas and honey when alkaloid-containing weeds are harvested with the crop. European food law sets maximum levels for pyrrolizidine alkaloids in herbal teas, teas, certain herbs and food supplements for exactly that reason.
Does comfrey work?
Graded D here: The better trials are negative, or the substance appears in the literature mainly for the harm it has caused. Swallowing, in any form, including comfrey tea and "knitbone" infusions. Also not for open wounds, broken skin or grazes.
How much comfrey should I take?
This reference does not print gram figures, because they do not transfer between preparations of different extract strength. What can be said honestly is the form and the duration: Creams, ointments and gels of alkaloid-depleted root or leaf extract, for external use on unbroken skin. Limited courses, and a limited total number of days per year — the restriction is on cumulative exposure, not on any single application.
What are the side effects of comfrey?
Externally, occasional skin irritation and contact allergy. Internally, liver injury that can be severe and irreversible.
Does comfrey interact with medicines?
Yes — documented for Liver load. Each one is described on this page, with a link to the medicine-side reference where one exists.
Others in where the harm is
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