Comfrey is a high-yielding leafy green plant that has been used for centuries as a feed crop for animals and a medicine for humans. However, in 2001, it was removed as an oral dietary supplement from the U.S. market, and, soon afterwards, as a commercial animal food source. These actions were taken because comfrey contains dangerous levels of toxic pyrrolizidine alkaloids and its use has led to severe liver injury and death.

Traditionally, oral or topical use of comfrey was said to help bones heal more rapidly, and this is the origin of its Latin name Symphytum (drawing together). It was also used orally for the treatment of digestive and lung problems. Topical comfrey creams have been used to treat minor wounds, bruises, sprains, and varicose veins.

Comfrey is commonly included in salves and creams that also contain such herbs as aloe, goldenseal, calendula, and vitamin E. Such preparations are marketed for treatment ofminor wounds. However, forsafety reasons, comfrey should not be applied to broken skin. Therefore, it should not be used for the treatment of lacerations or abrasions (cuts and scrapes).

There is some evidence that topical comfrey might be useful in the treatment of various conditions involving pain in the joints or muscles where skin is unbroken. Safety, however, does remain a concern.

In a double-blind, placebo-controlled study of 142 people with acute ankle sprain, use of comfrey cream for 8 days significantly enhanced rate of recovery.1Comfrey proved more effective than placebo in measurements of pain, swelling, and mobility. More modest benefits were seen in another double-blind trial, this one enrolling 203 people with ankle sprain and comparing a high-comfrey to a low-comfrey product.2

A double-blind, placebo-controlled study with 215 people found comfrey cream helpful for treatment of back pain.13In another randomized trial of 379 people with acute back pain, a topical combination of comfrey and methyl nicotinate cream reduced back pain (at rest and with movement), decreased functional impairment, and reduced use of rescue medication compared to methyl nicotinate cream alone or placebo.16

In a 3-week double-blind study of 220 people with osteoarthritisof the knee, comfrey cream reduced symptoms significantly more than a placebo cream.14

In a recent, well-designed trial, two concentrations of comfrey creams were evaluated for the treatment of fresh abrasions among 278 patients (almost a quarter of whom were under age 20).15 The higher concentration cream (10%) contained 10 times more comfrey than the low-concentration cream (considered the reference or placebo cream). The 10% comfrey cream led to significantly faster wound healing than the reference cream after 2 to 3 days of application. Although the researchers reported no adverse effects in either group, the use of comfrey has been associated with severe, even life-threatening toxic effects when used orally, and its use over open wounds must be undertaken with extreme caution.

Additional studies, generally of lower quality, suggest possible benefit for shoulder tendonitis and knee injuries.3

The active ingredients in comfrey are not known, but may include rosmaric acid, choline, and allantoin.