Cayenne contains a resinous and pungent substance known as capsaicin. Topical application of capsaicin relieves pain and itching by acting on sensory nerves.45 Capsaicin temporarily depletes "substance P", a chemical in nerves that transmits pain sensations. Without substance P, pain signals can no longer be sent. The effect is temporary. Numerous double-blind trials have proven topically applied capsaicin creams are helpful for a range of conditions, including nerve pain in diabetes (diabetic neuropathy),46, 47 post-surgical pain,48, 49, 50psoriasis,51 muscle pain due to fibromyalgia,52 nerve pain after shingles (postherpetic neuralgia),53, 54osteoarthritis pain,55, 56 and rheumatoid arthritis pain.57
With the aid of a healthcare professional, capsaicin administered via the nose may also be a potentially useful therapy for cluster headaches. This is supported by a double-blind trial.58 Weaker scientific support exists for the use of capsaicin for migraines.59
Injecting capsaicin directly into the urinary bladder has reduced symptoms of one type of bladder dysfunction (neurogenic hyperreflexic bladder)60 that results from spinal cord and other nerve injuries. Capsaicin is not known to help other bladder conditions, such as chronic bladder pain. The placing of cayenne or capsaicin products into the bladder has only been performed in clinical experiments and should only be done by a urologist.
Modest reductions in appetite have been found in healthy Japanese women and white men when they consumed 10 grams of cayenne pepper along with meals in a double-blind trial.61 A similar trial found that cayenne could increase metabolism of dietary fats in Japanese women.62 These trials suggest cayenne may help in the treatment of obesity.
In a double-blind study of people with dyspepsia (heartburn),
supplementation with 833 mg of cayenne powder in capsules, three times per day before meals, reduced heartburn symptoms by 48%, compared with a placebo. However, two of 15 individuals receiving cayenne discontinued it because of abdominal pain.63