In Germany, a double-blind, multicenter, randomized, placebo-controlled trial on 142 patients suffering from unilateral acute ankle sprains (mean age 31.8 years, 78.9% male) conclusively demonstrated the efficacy of a comfrey root extract ointment.  Treatment consisted of 4 applications per day for 8 days. Compared to placebo, comfrey treatment was superior in terms of pain reduction (tonometric measurement, p[less than]0.0001) and ankle edema (figure of eight method, p=0.000l). In relative terms pain was reduced by 63% for the active treatment after 8 days (vs 25% for placebo) and edema by 61% (vs 36% for placebo). Statistically significant differences between active treatment and placebo could also be demonstrated for ankle mobility and global efficacy. In terms of the latter, 81% of patients rated comfrey treatment as good or very good (vs 50% for placebo, p[less than]0.0009) and 86% of physicians rated comfrey as good or very good (vs 23% for placebo, p[less than]0.0001). No side effects were reported.
Comfrey contains potentially toxic unsaturated pyrrolizidine alkaloids (PA). In Germany the maximum allowed PA dosage from topical application is 100 [micro]g per day and treatment is limited to 4 to 6 weeks per year (for doses between 10 and 100 [micro]g per day). However these restrictions are not relevant to the test medication used in the trial which contained only 0.35 [micro]g/g of PA, resulting in a daily dose of PA well under 10 [micro]g.
The authors attributed their striking findings to the anti-inflammatory, antioxidant, antiexudative and healing properties of allantoin and rosmarinic acid, which are key components of comfrey. While this is certainly the case for effects of comfrey on the skin, with our current knowledge it is difficult to explain the deeper healing effect observed in the trial.
It is certainly true that there is a reasonable body of evidence for the anti-inflammatory and healing effects of comfrey on various skin conditions. A key component here is the allantoin which has been used for over 70 years as an 'effective' and 'non-irritating' skin moisturizer in cosmetics and toiletries. It acts on the non-keratin soluble cement matrix, binding the cornified cells of the horny layer of the skin and thus promoting the water binding ability or...
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