The following article review, written by Christina Chase, MS, RD, is from the American Botanical Council's (www.herbalgram.org) HerbClipâ„¢ Education Mailing Service. The article is from a 2001 issue of the Journal of Nutraceuticals, Functional and Medical Foods. For more information, see the credit at the end of this article.
Capsaicin is the primary pungent compound found in the hot pepper plant (genus Capsicum). The chemical name of capsaicin is trans-8 methyl N-vanillyl-nonenamide. Recently, clinical studies have confirmed that capsaicin has analgesic properties when applied topically.
The clinical evidence of capsaicin's analgesic effects is supported by research revealing two possible mechanisms of action. One mechanism is neuronal, and the other is receptor-mediated. The neuronal mechanism is as follows: capsaicin depletes substance P, a neuropeptide, from a specific type of sensory neuron (nerve cell). When capsaicin is first applied to the skin, it causes release of substance P, which leads to redness and a burning sensation. However, if capsaicin is applied regularly, the cumulative exposure to capsaicin depletes substance P and desensitizes the sensory neurons. Eventually the neurons become inactive, and pain sensation is reduced.
The receptor-mediated mechanism is not yet completely understood. It appears that capsaicin's effects are moderated by a receptor-ligand interaction. One theory is that capsaicin and its analog (similar substance) resiniferatioxin both can bind to a single receptor that is also the binding site of capsazepine, the competitive antagonist of capsaicin. Further research has updated this theory, suggesting that a group of similar receptors, the vanilloid receptor family, may be involved. Future research on the vanilloid receptor model may prove promising in elucidating the topical mechanism underlying capsaicin's analgesic effects.
The authors review the clinical research on use of capsaicin for pain relief in three medical conditions: osteoarthritis, postmastectomy pain syndrome, and postherpetic neuralgia. Postherpetic neuralgia is a painful condition that often follows acute herpes zoster infection (shingles). Among patients aged 60 years and older, 50% of those who recover from shingles develop postherpetic neuralgia. The pain has been described as severe and unrelenting, and it may be accompanied by loss of appetite, insomnia, and constipation. The available treatments include potent analgesics and psychoactive drugs, but various drugs have been found ineffective. One study compared 0.075% capsaicin cream to an inert (placebo) cream in 32 patients, aged 54 to 90 years, who had had postherpetic neuralgia for at least 12 months. After four weeks of treatment, 77% of the capsaicin group reported reduced pain compared with 31% of the placebo group. The results showed that capsaicin was both safe and effective.
Osteoarthritis is usually treated with non-steroidal anti-inflammatory drugs or salicylates, but these drugs have been associated with serious side effects including gastrointestinal bleeding and impaired kidney and liver function. Therefore, new treatment approaches are greatly needed. A small, double-blind, placebo-controlled study was conducted on 21 patients with either osteoarthritis or rheumatoid arthritis. The study compared 0.075% capsaicin cream, applied to affected areas four times daily, to a placebo cream. "Results showed that the capsaicin cream reduced pain and tenderness of osteoarthritis of the hands by 40% as compared to the control group, but had no effect on grip strength, joint swelling or morning stiffness,"? the authors report. The rheumatoid arthritis patients reported no improvement with either capsaicin or the placebo.
Capsaicin was also evaluated as a treatment for postmastectomy pain syndrome. In a double-blind, randomized study, 25 patients were treated with either 0.075% capsaicin cream or an inert cream for six weeks. The capsaicin-treated group reported a significant improvement in pain relief; 46% of these patients were satisfied with the degree of pain relief they experienced. The placebo group did not report a significant change in pain relief.
In summary, studies on clinical effectiveness and underlying mechanisms support the analgesic potential of capsaicin. However, the authors caution that “not all disorders show similar results with capsaicin treatment and...this review represents only a sampling of the available therapeutic studies using capsaicin.� As an analgesic, capsaicin has the advantages of being non-addictive and also a natural substance. "Capsaicin is a safe and effective alternative in the pain relief of a variety of medical conditions. The natural aspect of this treatment, in comparison to synthetic drugs, may be the most appealing factor in patient care," the authors conclude.
The American Botanical Council (ABC) is the world's leading non-profit education organization disseminating science-based information promoting the safe and effective use of herbal medicine. This review was originally distributed as part of the HerbClipâ„¢ Educational Mailing Service. HerbClip and HerbalGram are among the benefits of membership in ABC. To join ABC, logon to www.herbalgram.org or call 800-373-7105, or email abc@herbalgram.org.
