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Posted on Sat, Nov 26, 2011 : 5 a.m.

Capsaicin gets mixed results for arthritis pain relief

By Ask Dr. K


I have pain from osteoarthritis in both knees. I'm curious about creams made from a substance in hot peppers. How do they relieve pain? Are there other pain medications that can be applied to my skin, so I don't have to take a pill?


You're referring to capsaicin, the substance in chili peppers that gives them their hot taste. Capsaicin is an ingredient in many over-the-counter topical pain-relief preparations, which include creams, gels, lotions, patches and sticks.

When first applied, topical capsaicin causes a burning sensation. This sensation lessens within a few minutes, and it also gets less intense with repeated applications. Aside from the burning feeling, there are few, if any, side effects.

Doctors don't know exactly how capsaicin works, but they think it stimulates the release of substance P, a chemical that helps relay pain signals from sensory nerve fibers to the brain. After several applications of capsaicin, the substance P in that area is used up and levels go down. This causes the nerve fibers in that area to transmit fewer pain signals.

Studies comparing topical capsaicin with a placebo for arthritis pain have produced inconsistent results. Some studies have shown topical capsaicin to be more effective than a placebo, but other research has shown only a moderate to poor benefit.

Capsaicin might be helpful when it's used along with other pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs). It may also be useful for people who can't tolerate other pain-relief treatments.

Capsaicin provides only temporary relief, so it must be applied four times a day. Before you use it on a large area, test it on a small patch of skin to make sure you're not allergic to any of the ingredients. Then apply enough to cover the painful area and rub it into your skin until it disappears. Finally, be sure to wash your hands thoroughly to avoid accidentally getting capsaicin into your eyes, nose or mouth.

Don't apply capsaicin to broken or irritated skin, and don't use a heating pad on the area you're treating. It may be a week or so before you feel the full effect on your knee pain. If you don't notice any improvement after four weeks, stop using capsaicin.

If you are interested in other topical medications to control your osteoarthritis pain, some options are available.

A prescription NSAID, diclofenac, is available for topical use as a gel (Voltaren gel) and a patch (Flector Patch). Both carry some of the same risks as oral NSAIDs, but they are less likely to cause stomach and intestinal irritation because they don't enter the gastrointestinal tract. If you develop an upset stomach when taking an oral NSAID, consider trying one of the topical versions. Non-prescription ointments that contain methyl salicylate, menthol and camphor are among the other popular topical pain relievers.

Whenever you apply a medication to your skin, it's important to avoid touching any of your mucous membranes (for example, around your mouth, nose or eyes) after applying the cream, to avoid irritation.

While the notion of applying medicine right to the spot that hurts has obvious appeal, there are some doubts about whether such remedies work. With something as subjective as pain, it can be hard to figure out whether a treatment is effective.

For example, an ointment that provides a soothing sensation might be said to work by some definitions. And the placebo effect -- a benefit that comes from the patient's expectations rather than the treatment itself -- is a major complicating factor.

On the other hand, there's no question that active medicine can penetrate the skin and get into the body; how much is absorbed is a separate question. And, at least in theory, exposing just the painful part of the body to a medicine might mean fewer side effects than taking a pill, which involves gastrointestinal absorption and the drug being carried in the blood throughout the entire body.

Topical pain medication may provide temporary relief from arthritis pain. But you may get more durable relief from special exercises and weight loss. So if your goal is to reduce pain with a minimum of medication, discuss all these options with your doctor or physical therapist.

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