Capsaicin, which makes peppers hot, can cause prostate cancer cells to kill themselves.  Capsaicin led 80 percent of human prostate cancer cells growing in mice to commit suicide in a process known as apoptosis. Prostate cancer tumors in mice fed capsaicin were about one-fifth the size of tumors in untreated mice. Capsaicin had a profound anti-proliferative effect on human prostate cancer cells in culture. It also slowed the development of prostate tumors formed by those human cell lines grown in mouse models. The mice ate the human equivalent of 400 milligrams of capsaicin three times a week. That is about the amount found in three to eight fresh habanero peppers, depending on how hot the peppers are.

Capsaicin and pancreatic cancer
Capsaicin, when fed to mice, causes apoptosis death in pancreatic cancer cells. The spicy compound kills pancreatic tumor cells but does not affect normal, healthy pancreas cells.

Capsaicin for pain relief
Danish researchers say purified capsaicin reduces pain for at least three days following groin hernia surgery without causing any significant side effects. Dr. Eske Aasvang and colleagues at the Juliana Marie Center in Copenhagen, Denmark, tested 41 men getting hernia operations. Half got injections of purified capsaicin, which is odorless and tasteless. The rest got placebos. All of the men also got the painkillers ibuprofen and acetaminophen. The men injected with capsaicin had significantly less pain during the three days after surgery than those given placebo.

Capsaicin skin patch for HIV patients
Treatment with a high-concentration capsaicin skin patch is a well-tolerated method of reducing the neurological pain in patients with HIV infection. Journal of Pain and Symptom Management, March 2008.

Capsaicin Research
Effects of capsaicin on P-gp function and expression in Caco-2 cells.
Biochem Pharmacol. 2006 Apr 18; Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
Capsaicin is the pungent component of hot chilli, a popular spice in many populations. The aim of the present study was to evaluate the chronicity and reversibility of the modulating effect of capsaicin on both the P-gp expression and activity in the Caco-2 cell monolayers. Capsaicin at concentrations ranging from 10 to 100muM, which were found to be non-cytotoxic towards the Caco-2 cells, were observed to inhibit P-gp mediated efflux transport of [(3)H]-digoxin in the cells. The acute inhibitory effect was dependent on the capsaicin concentration and duration of exposure. In summary, our data suggest that caution should be exercised when capsaicin is to be consumed with drugs that are P-gp substrates. In particular, the oral bioavailability of these drugs may be influenced by the P-gp status of populations that rely heavily on hot chilli in their diets.