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
vitamin E. Such preparations are marketed for treatment of minor wounds. However, for safety 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.1 Comfrey 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.13 In 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
osteoarthritis of 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
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.
The tested form of topical comfrey contains 10% of a 2.5:1 juice extract made from fresh pressed plant sap; in other words, every 100 grams of cream contains the equivalent of 25 grams of comfrey sap.
As noted above, comfrey contains substances called pyrrolizidine alkaloids that are both toxic to the liver and carcinogenic.5-12
The main form of liver disease seen with comfrey is a blockage of small veins that can lead to liver cirrhosis and eventually liver failure (hepato-occlusive disease). Liver transplantation may be required.
Oral use of comfrey for as brief a time as 5 to 7 days in a child and 19 to 45 days in adults has resulted in severe liver disease and death. Long-term use of very low dosages may also cause harm.
In general, the root of the plant contains more pyrrolizidine alkaloids than the leaves. Related species of comfrey such as
contain even higher levels of these toxins, and may be mistakenly sold as ordinary comfrey.
Pyrrolizidine alkaloids in comfrey can be absorbed through the skin. For this reason, it has been recommended that when using comfrey preparations, the daily amount of pyrrolizidine alkaloids should not exceed 100 mcg. Unfortunately, few products are labeled to indicate their pyrrolizidine alkaloid content. Furthermore, the common analytic methods used for testing pyrrolizidine alkaloid content may fail to measure a certain chemical form of these toxins (the N-oxide form), leading to results that are too low by a factor of ten or more. For all these reasons, it may be prudent to avoid topical comfrey products entirely. If you nonetheless wish to use comfrey as a topical treatment, we recommend the following general guidelines:
- Do not apply comfrey for more than 4-6 weeks per year.
- Do not use for more than 10 days in a row.
- Do not apply to broken skin.
In addition, comfrey should not be used by children, pregnant or nursing women, or people with liver disease.
Koll R, Buhr M, Dieter R et al. Efficacy and tolerance of a comfrey root extract (Extr. Rad. Symphyti) in the treatment of ankle distorsions: results of a multicenter, randomized, placebo-controlled, double-blind study.
Kucera M, Barna M, Horacek O, et al. Efficacy and safety of topically applied
herb extract cream in the treatment of ankle distortion: results of a randomized controlled clinical double blind study.
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Oberlies NH, Kim NC, Brine DR, et al. Analysis of herbal teas made from the leaves of comfrey (
Symphytumofficinale): reduction of N-oxides results in order of magnitude increases in the measurable concentration of pyrrolizidine alkaloids.
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Yeong ML, Wakefield SJ, Ford HC. Hepatocyte membrane injury and bleb formation following low dose comfrey toxicity in rats.
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Yeong ML, Clark SP, Waring JM, et al. The effects of comfrey derived pyrrolizidine alkaloids on rat liver.
Kucera M, Barna M, Horacek O et al. Topical symphytum herb concentrate cream against myalgia: a randomized controlled double-blind clinical study.
Grube B, Grunwald J, Krug L, et al. Efficacy of a comfrey root (Symphyti offic. radix) extract ointment in the treatment of patients with painful osteoarthritis of the knee: results of a double-blind, randomised, bicenter, placebo-controlled trial.
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Barna M, Kucera A, Hladicova M, et al. Wound healing effects of a Symphytum herb extract cream (Symphytum x uplandicum NYMAN): Results of a randomized, controlled double-blind study.
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Pabst H, Schaefer A, et al. 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):811-817.
Last reviewed September 2014 by EBSCO CAM Review Board
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