Capsaicin

Capsaicin, the active component derived from the fruit of capsicum, is used to relieve pain, improve circulation, to treat cluster headaches and psoriasis, and for weight loss. Capsicum or cayenne pepper, a shrub prevalent in many tropical and subtropical climates, is an important ingredient of many cuisines around the world. It has been used in traditional medical systems as a remedy for digestive and circulatory problems, poor appetite, and to relieve muscle and arthritic pain. Capsaicin is marketed in capsule form and as an ingredient in topical creams. A prescription-strength dermal capsaicin product, approved by the FDA, is available for the management of postherpetic neuralgia.

Capsaicin is thought to reduce pain sensation by temporarily depleting a neurotransmitter, substance P, which relays pain signals to the brain.
Studies support benefits of topical capsaicin for psoriasis ⁽⁵⁾, prurigo nodularis ⁽⁶⁾, pruritis ani ⁽¹⁵⁾, of intranasal application for rhinitis ⁽¹⁶⁾ and for cluster headaches ⁽⁸⁾. A dermal capsaicin patch was shown safe and effective for the treatment of postherpetic neuralgia ⁽²⁴⁾.
Intravesical capsaicin injections were shown to induce diuresis ⁽⁷⁾. A small study found improved hair growth with a combination of capsaicin and isoflavone in healthy volunteers with alopecia ⁽¹⁸⁾.
Capsaicin cream did not relieve HIV-associated distal symmetrical peripheral neuropathy ⁽²⁾ and a review of studies of capsaicin for neuropathic pain associated with HIV, diabetes, and mastectomy concluded that available data are limited to enable full assessment of its benefits ⁽¹⁹⁾. Its utility for arthritic pain also remains inconclusive ^{(3) (4)}.

Capsaicin, originally thought by some to be a carcinogen, was shown to be safe in animal studies ⁽¹⁰⁾. Interestingly, it demonstrated chemopreventive ⁽¹⁷⁾ and antiproliferative ⁽²⁶⁾ effects against prostate cancer cells. A case report of a patient with prostate cancer suggests that capsaicin may slow doubling time of prostate specific antigen (PSA) ⁽²⁵⁾. Data also suggest that capsaicin cream can effectively control post-surgical pain in cancer patients ⁽¹⁾.