General Info
When Carolus Linneus first identified the genus Capsicum in the mid-1700s, there were only two species. By the 1900s, more than 100 cultivated species of Capsicums have been described. However, the variations were so minor that horticulturists have distilled the list anew to two: c. annuum, which includes cayenne peppers and chiles, as well as bell peppers, and C. fructescens, which is the pepper from which Tabasco sauce is made.

Capsaicin is the active ingredient in the extract of hot peppers. It is most concentrated in the rib or membrane, less in the seeds, least in the flesh. Capsaicin for medicinal use comes from Capsicum fructescens, a species of the cayenne pepper.

Mechanism of Action
Capsaicin depletes substance P in afferent type C sensory nerve fibers and affects only proprioception. Unlike other treatments for neuropathy, such as local anesthetics, opiates, anti-seizure medications or tricyclic antidepressants, capsaicin specifically treats pain without impairing other aspects of the nervous system. In incomplete depletion of substance P from suboptimal use, it may cause parodoxical increase of pain.

Uses
Post-herpetic neuralgia, post-mastectomy pain, hemodialysis-associated pruritus, psoriatic itching and pain, painful neuropathies, especially diabetic neuropathy, and other superficial neuropathies.

In a double-blind placebo-controlled trial, topically applied capsicum cream provided significant relief from soft tissue pain. 281 patients with musculoskeletal pains of the back, shoulder, and neck were randomized to a placebo cream or a cream with 2.5 g/100 g capsicum extract, both applied three times daily for 21 days. There wre 74% (103) responders in the active group vs 48% (63) in the placebo group, a difference that is statistically significant. The treatment was well tolerated with only 19 adverse events - 13 in the capsicum group (2, excessive heat; one, pruritus) and 6 in the placebo group. The effect was attributed to the depletion of the neurotransmitter involved in transmission of pain signals to the brain.

Doses
Creams of varying potency from 0.01% and 0.075% applied 4-5 times daily for at least four weeks. Because of local side effects, it is advisable to start with low potency creams and increasing in potency as tolerated. Less frequent application, such as once or twice daily, can actually lead to increased pain. Older patients, especially those with long-standing post-herpetic neuralgia, may require several years of therapy and may even need lifelong treatment.Capsaicin is also available as fresh and dried peppers, capsules, tablets, and tinctures.

Precautions
Because of potential respiratory toxicity, avoid concentrations greater than 0.1%. Higher concentrations are also more likely to cause local chemical irritation. Wear gloves during applications, avoiding contact with eyes and mucous membranes; do not use on open abrasions and open wounds.

Formulation
Approved for external application, capsaicin is also available as tablets, capsules and tinctures.

Capsaicin and Dyspepsia
In a small trial in Italy (Dr. Mauro Bortolotti et al, University of Bologna), 30 patients with functional dyspepsia were randomized on daily capsules of 2.5 g of red pepper or placebo. The capsaicin content (trans-8-methyl-N-vanillyl-6-nonenamide) was 0.7 mg/g of red pepper power. After 3 weeks, upper gastrointestinal symptoms of epigastric pain, fullness, nausea and early satiety were all significantly reduced in the capsaicin group and not in the placebo group. The mechanism of action is believed to be the desensitization of gastric nociceptive C fibers, which carry pain sensations to the central nervous system. (NEJM.346[12]:947-48,2002) Clinical Capsules. Internal Medicine News. May15,2002