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Botanical Description & Habitat

Symphytum officinale


Common Names

Healing herbKnitback
Slippery rootWallwart

North America, Europe, and western Siberia; found in moist, watery places.

Comfrey is a perennial plant; its rootstock is fleshy and branched, with a white interior. It produces an angular hairy stem, which grows up to 3 feet in height, branching only near the top. The green leaves are large, oblong, and lanceolate, with a rough texture and covering of short hairs; basal leaves usually lie on the ground. Whitish or pale purple flowers grow in racemes from the upper leaf axils, blooming from May to August. The fruit consists of 4 small nuts located at the bottom of the calyx.

Medicinal Parts
Root and rhizome - dried, collected in spring and autumn.

Historical Properties & Uses

Comfrey was once one of the most popular herbs around, but recent word of possible toxicity has caused a sharp decrease in its use. Little is fully understood about the problem. Complicating the question is the fact this particular type of poisoning (due to pyrrolizidine alkaloids) can take several months or years to appear, and is seldom directly traceable to any one cause. Such uncertainty about its safety leads many people to simply avoid ingesting it.

Externally, there appears to be no danger. Since many of comfrey's most valuable uses are external, it remains a beneficial part of herbal medicine. Its active component, allantoin, is used in many commercial topical preparations. Applied to open wounds, it reduces inflammation and helps heal the wound by promoting new cell growth. Skin conditions successfully treated with comfrey or allantoin include psoriasis and burns. When applied as a poultice or pomade, comfrey has also been used on varicose veins, fractures, pleurisy, rheumatism, and bronchitis.

While hundreds of case studies attest to the herb's utility in most of the above conditions, some (varicose veins, pleurisy, rheumatism, and bronchitis) have not yet been substantiated experimentally.

Comfrey remains popular in Germany, where the entire herb (leaf and root etc.) has been approved by the Commission E as a topical preparation for bruises and sprains and maintains a leading position in the sales for phytopharmaceuticals: almost $5 million.


Blumenthal, M (Ed.): The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. American Botanical Council. Austin, TX. 1998.

Method of Action

Comfrey has antibacterial properties
Comfrey has good antimicrobial properties which are due to caffeic acid and phenolic esters. It also has some antitubercular activity.

Comfrey and allantoin have good skin healing action
Allantoin is the constituent in comfrey responsible for its ability to heal skin disorders. Pure allantoin is produced by many manufacturers for the purpose of stimulating the growth of healthy tissue to heal wounds and resistant ulcers.

Allantoin is generally recognized as a cell proliferator, which would explain its folklore uses as a wound healer.

The use of allantoin in medicine followed the use of fly maggots during World War I. Osteomyelitic abscesses and severe wounds were treated during the war with maggots, after it was found such conditions healed faster when infested with fly maggots. Allantoin was found to be present in the larvae and was promptly substituted as a cell proliferator. Later, it was found urea was the effective molecule in allantoin, and so urea has become the standard treatment.

Some studies have found allantoin is effective in the treatment of psoriasis, while other studies have found no beneficial effect at all.

Allantoin has been combined with silver nitrate to form a burn treatment. Initial investigations with the compound proved effective and very promising.

Comfrey has anti-asthmatic and anti-inflammatory properties
Some research suggests that fresh uncooked comfrey leaves and roots are efficacious in relief of asthma.

The anti-inflammatory property has received some positive support in the literature.

Drug Interactions & Precautions

Possible Interactions
If comfrey is being used on a daily basis, the following drugs may be imperfectly absorbed: tetracycline derivatives, oral anticholinergics, phenothiazines, digoxin, isoniazid, phenytoin, and warfarin.

The urinary excretion of alkaline drugs, such as amphetamines or quinidine, may be inhibited by the antacid nature of comfrey. The antacid nature of comfrey may also decrease or delay the absorption of nalidixic acid and the sulfonamides.

The antituberculous activity of comfrey may potentiate the adverse effects of other antituberculous drugs, especially ethionamide.

The anti-inflammatory activity of comfrey can be seriously inhibited by phenobarbital and certain other sedatives and hypnotics, such as chloral hydrate and meprobamate. This is also true of beta-adrenergic blocking agents, such as propranolol.

The topical application of the astringent herb comfrey, in conjunction with the acne product tretinoin (retinoic acid, vitamin A acid), may adversely affect the skin.

The antacid properties of comfrey may enhance the renal tubular resorption of the antiarrhythmic drug, quinidine, leading to increased quinidine serum levels.

Since comfrey's action depends on the presence of cholinergic substances, its action will be affected by the decrease in cholinergic-receptor stimulation produced by anticholinergics.

Safety Factors & Toxicity

The FDA currently classifies Comfrey as a toxic substance.

Comfrey is a member of the family Borageinaceae which is noted for its many species containing hepatotoxic pyrrolizidine alkaloids. These alkaloids are metabolized by the liver through dehydrogenation to reactive pyrrole-like derivatives which are really the toxic substances. Comfrey also contains a good share of these toxic, tumor- and lesion-promoting chemicals. There are, however, several species of comfrey itself, and they vary in the amount of alkaloids present. Within a species, total alkaloid content varies with time of year, age of plant, and size of leaves. In general, larger and more mature leaves, gathered late in the fall will have the least toxicity.

S. officinale extracts have been shown to cause hepatocellular adenomas. These liver tumors occurred more often in groups of experimental rats fed comfrey root than in groups fed comfrey leaf. Concentrations of root of 4% affected many rats, whereas concentrations of leaf as high as 33% did not adversely affect the animals. The root is therefore much more toxic than the leaf. Toxicity of the leaf to humans is probably quite small. It has been pointed out toxicological data on the chronic effects of pyrrolizidine alkaloids in humans are scarce because the effects of such poisoning take several months or years to become noticeable. What evidence does exist is open to dispute as far as critical parameters such as dosage were concerned.

Protein extracted from comfrey is not toxic.

Comfrey (herb, leaf and root) has approval status by the German Commission E.

The German Commission E recommends a limited duration for the use of this herb of not more than 4 - 6 weeks in a year.


Blumenthal, M (Ed.): The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. American Botanical Council. Austin, TX. 1998.

Preparation & Administration

Three times a day

Dried leaf
2-4 grams

made from 1 tsp dried leaf

Fluid extract
1:1 in 25% alcohol, 2-4 ml

This herb has approval status by the German Commission E.

Recommended daily dosages in Germany are as follows:

External ointments have 5 - 20% dried drug (above or below ground parts).

The German Commission E recommends a limited duration for the use of this herb of not more than 4 - 6 weeks in a year.

Note: This Herbal Preparation information is a summary of data from books and articles by various authors. It is not intended to replace the advice or attention of health care professionals.


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Bressler, R., M.D. Bogdonoff & G.J. Subak-Sharpe. 1981. The Physicians Drug Manual. Doubleday & Co, Inc. Garden City, NY. 1213 pp.

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De Martinis, et.al. Milk thistle (silybum marianum) derivatives in the therapy of chronic hepatopathies. Clin. Ter., 94(3). pp. 283-315. 1980.

Drug package insert (FDA approved official brochure) and other labeling based on sponsored clinical investigations and New Drug Application data.

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Kastrup, E.K., ed. 1981. Drug Facts and Comparisons, 1982 edition. Facts and Comparisions Division, J.P. Lippincott Co, Phila(St. Louis).

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Riesterer, L. & R. Jaques. 1968. Interference by beta-adrenergic blocking agents with the antiinflammatory action of various drugs. Helv Physiol Acta, 26. pp. 287-293.

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Scientific Committee, British Herbal Pharmocopaeia, British Herbal Med Assoc, Lane House, Cowling, Na Keighley, West Yorks, Bd Bd220lx, l983

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Yeong, ML et al., Hepatic veno-occlusive disease associated with comfrey ingestion. J or Gastroent. Hepatol. 1990, 5(2):211.

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Symphytum officinale

? Southwest School of Botanical Medicine