Comfrey (Symphytum officinale) has been traditionally used to treat wounds and to reduce the inflammation associated with sprains and broken bones. The roots and leaves of comfrey contain allantoin, a substance that promotes wound healing and tissue regeneration. Comfrey ointments were often applied to the surface of the skin to heal bruises as well as pulled muscles and ligaments, fractures, sprains, and strains. Some traditional healers also used comfrey leaves to reduce inflammation, treat gout, and heal superficial blood clots in the legs (called thrombophlebitis).

Despite these beneficial effects, reports began to emerge in the 1980s that internal consumption of comfrey may be hazardous to the health. Laboratory studies revealed that comfrey contains dangerous substances called pyrrolizidine alkaloids that are highly toxic to the liver. Animal studies found that consumption of comfrey may lead to a potentially life-threatening condition called hepatic veno-occlusive disease (HVOD) in which the blood vessels around the liver become blocked. If left untreated, HVOD can lead to complete liver failure, even death. Outbreaks of HVOD began to appear in Europe and the United States and researchers gradually discovered that these outbreaks were often linked to ingestion of oral comfrey products.

Echimidine is one of the most toxic pyrrolizidine alkaloids. Dangerously high levels of this alkaloid have been found in both prickley comfrey (Symphytum asperum) and Russian comfrey (Symphytum uplandicum), close relatives of the common comfrey plant. While common comfrey has been the preferred source of comfrey herbal products, some preparations sold in the United States and Europe may have been unknowingly contaminated with Russian and prickley comfrey. This is because common, Russian, and prickley comfrey are very similar in appearance and collectors who harvest raw plant material are not always able to distinguish between the different species.

Based on reports of HVOD in the United States and abroad, the U.S. Food and Drug Administration (FDA) recommended in July of 2001 that dietary supplement manufacturers immediately remove all comfrey-containing products from the market. The FDA cited evidence that the pyrrolizidine alkaloids are not only toxic to the liver, but possibly other tissues in the body as well. They also cited evidence that these substances may even potentially cause cancer. In addition to the United States, countries including the United Kingdom, Australia, Canada, and Germany have banned the sale of products containing comfrey. Other countries permit use of this herb only under a doctor's prescription.

Comfrey is a perennial herb that originated in Europe and temperate parts of Asia. Fond of moist soils, comfrey has an erect and stiff-haired stem, and it grows to a height of 20 to 120 cm. Its flowers are dull purple, violet, or whitish, and densely arranged in clusters. The wrinkly and hairy leaves are oblong, and often differ in appearance depending upon their position on the stem: the lower leaves are broad at the base and tapered at the ends while the upper leaves are broad throughout and narrowed only at the ends. The slimy roots show a horn-like appearance when dried. The root has a black exterior and fleshy whitish interior filled with juice.

Comfrey preparations are made from the leaves or other parts of the plant grown above the ground. Some preparations were also made from the roots, but roots contain up to 16 times the amount of pyrrolizidine alkaloids and are therefore more likely to cause poisoning.

Comfrey contains allantoin, rosmarinic acid, and vitamin B12. It also contains poisonous compounds called pyrrolizidine alkaloids, which are highly concentrated in the roots of the comfrey plant. In fact, the roots contain levels of pyrrolizidine alkaloids that are roughly 10 to 16 times higher than the mature leaves.

Oral comfrey products have been restricted by the FDA, but topical preparations are still available in the United States.

Comfrey ointments (containing 5% to 20% comfrey), creams, poultices, and liniments are made from the fresh or dried herb, leaf, or root of comfrey species. Use only products made from leaves of common comfrey.

Be sure to buy comfrey preparations from established companies with good reputations, and who distribute their products through trustworthy and knowledgeable establishments. Whenever possible, select products with guaranteed potency or standardized extracts. Follow dosage recommendations on the label.

Pediatric

Children should never ingest comfrey or comfrey-containing products for any reason.

There are no known scientific reports on the pediatric use of topical comfrey ointments or creams. Therefore, it is not currently recommended for children.

Adult

Adults should never ingest comfrey or any comfrey-containing products.

Use only herb and leaf ointments, creams, and other topical preparations. Use only the amount recommended on the label and never more than this amount. Comfrey remedies should not be used for more than four to six weeks in any given year.

Comfrey contains toxic substances that can cause severe liver damage and possibly even death. For this reason, comfrey and comfrey-containing products should never be ingested. The main symptom you would feel if experiencing liver damage from comfrey is abdominal pain just below the right side of the rib cage because the liver enlarges from HVOD.

Because of the potential for side effects and interactions with medications, even topical comfrey preparations should be taken only under the supervision of a knowledgeable healthcare provider.

Comfrey is considered relatively safe if used only as a topical preparation on unbroken skin (free of cuts or open wounds).

Pregnant and breastfeeding women should not use comfrey products under any circumstances.

There are no known scientific reports of interactions between comfrey and conventional medications.

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