Capsaicin (Capsicum frutescens)

Origin: The highly purified, heat-producing component in chili peppers

What we know: Applied as a topical cream, gel or patch, capsaicin works by depleting the amount of a neurotransmitter called substance P that sends pain messages to the brain. For the first couple of weeks of use, it may cause burning or stinging as substance P is released and ultimately depleted; it must be used regularly to keep substance P from building up again.

Studies: Many studies have shown that capsaicin effectively reduces pain from osteoarthritis, rheumatoid arthritis and fibromyalgia. In a 2010 German study, joint pain decreased nearly 50 percent after three weeks' use of 0.05 percent capsaicin cream.

Dosage: Most capsaicin products – such as Zostrix, Zostrix HP, Capzasin-P and others – contain between 0.025 to 0.075 percent concentrations. Apply regularly three times daily.

Capsaicin can cause burning and irritation. Avoid applying it near your eyes or on sensitive skin.