Traditional muscle rubs containing salicylate – an aspirin-like compound – do not help much, according to a recent review by British researchers for the Cochrane Collaboration, an international nonprofit that provides up-to-date information on health care research. But American doctors say that newer topical NSAIDs (non-steroidal anti-inflammatory drugs) containing diclofenac may be more effective.
In the Cochrane review, researchers from the University of Oxford looked at seven randomized, controlled trials of muscle rubs containing salicylates for acute pain, and nine randomized, controlled trials for chronic pain involving a total of 1,276 people. The rubs caused irritation and reddening of the skin by stimulating blood flow, which has been theorized to relieve certain kinds of muscle pain.
Overall, the researchers found, there’s not enough evidence to support the use of gels or creams containing salicylates.
In the last several years topical NSAIDs have entered the US market. These prescription drugs (the Flector Patch and Voltaren Gel, both of which contain diclofenac) are “somewhat effective for treating the chronic pain of osteoarthritis,” says Dr. James P. Rathmell, chief of the Division of Pain Medicine at Massachusetts General Hospital. “But only one in three patients will get more than 50 percent pain relief.”
There are also over-the-counter rubs such as BenGay, Icy Hot, and Zostrix. The first two contain menthol and Zostrix contains capsaicin. Menthol and capsaicin activate a class of receptors called TRP (Transient Receptor Potential), found on sensory neurons, says Rathmell.
In general, a major problem with any of the topical treatments is that they don’t get deeply enough into muscle tissue to provide much relief, says Dr. Robert Simms, chief of rheumatology at the Boston University School of Medicine.
“It is reasonable to try this stuff,” says Rathmell, “but don’t expect miracles. The pain relief is modest and more than half of people will not get any significant relief.”