Clinical Question: Is topical capsaicin effective in the treatment of neuropathic or musculoskeletal pain?
Setting: Outpatient (any)
Study Design: Meta-analysis (randomized controlled trials)
Synopsis: This meta-analysis combined the results of 16 double-blind randomized studies comparing topical capsaicin with placebo in the treatment of musculoskeletal or neuropathic pain in 1,556 patients. Studies were identified by a thorough search that included numerous databases, including an in-house database of 13,000 studies in pain research. The search and data extraction processes were appropriate. After four weeks of treatment, capsaicin, applied three to four times daily, was significantly better than placebo in the treatment of neuropathic and musculoskeletal pain, defined as the percentage of patients achieving a 50 percent reduction in pain (i.e., “none” or “slight” pain on rest or movement or “good” or “excellent” overall assessment of treatment).
For neuropathic pain, more than one half of the patients receiving capsaicin (57 percent; range in studies: 53 to 75 percent) had this degree of improvement compared with 42 percent of patients receiving placebo (range: 31 to 55 percent). For every seven patients treated with capsaicin instead of placebo, one patient will benefit (number needed to treat [NNT] = 6.4; 95 percent confidence interval [CI], 3.8 to 21). Results after eight weeks of treatment were similar. For musculoskeletal conditions, the treatment benefit was less, with 38 percent of patients responding to the capsaicin compared with 25 percent responding to placebo (NNT = 8; 95 percent CI, 4.6 to 34). Significantly more adverse events occurred with capsaicin than placebo (number needed to treat to harm [NNTH] = 3). Withdrawals because of adverse events occurred in 13 percent of the capsaicin group and 3 percent of the placebo group (NNTH = 9.8; 95 percent CI, 7.3 to 15.0).
Bottom Line: A little more than one half of the patients with neuropathic pain (57 percent) will achieve a good reduction in pain with the use of topical capsaicin, although there is a significant placebo response (42 percent). Results with capsaicin are not as good for musculoskeletal pain, with a 38 percent response to treatment and a 25 percent response to placebo. More than one of every three patients using capsaicin will experience an adverse effect, and approximately one in eight will stop using the drug because of side effects. This therapy should be saved for those few patients who have exhausted other options. (Level of Evidence: 1a)