Capsaicin,(8-methyl-N-vanillyl-6-nonenamide, (CH3)2CHCH=CH(CH2)4CONHCH2C6H3-4-(OH)-3-(OCH3)) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact. Capsaicin and several related compounds are called capsaicinoids and are produced as a secondary metabolite by chili peppers, probably as deterrents against certain herbivores and fungi. Pure capsaicin is a hydrophobic, colorless, odorless, crystalline to waxy compound.
We know that many pain killer gels are using this and even some companies are trying to establish the anti cancer activity (prostate cancer).
Mode of action :
The burning and painful sensations associated with capsaicin result from its chemical interaction with sensory neurons. Capsaicin, as a member of the vanilloid family, binds to a receptor called the vanilloid receptor subtype 1 (VR1). The resulting depolarization of the neuron stimulates it to signal the brain. By binding to the VR1 receptor, the capsaicin molecule produces the same sensation that excessive heat or abrasive damage would cause, explaining why the spiciness of capsaicin is described as a burning sensation.
Now FDA has approved the Qutenza(TM) (capsaicin) 8% patch, the first and only product containing prescription strength capsaicin, for the management of neuropathic pain due to postherpetic neuralgia (PHN). As per the claim by the company, Qutenza works by targeting certain pain nerves in the area of skin where pain is being experienced. The Qutenza patch is applied by a physician or a healthcare professional. Clinical studies have shown that PHN pain can be reduced for up to 12 weeks following a single one-hour treatment. Up to four patches may be used and patches may be cut to conform to the size and shape of the painful area.
Source : http://ngsx.client.shareholder.com/releasedetail.cfm?ReleaseID=424559