Melatonin is a hormone produced naturally by the body's pineal gland, located at the base of the brain. This gland secretes the hormones serotonin and melatonin. Melatonin is also secreted by the intestines, regulating intestinal health, healing and peristalsis. Some people consider melatonin a complementary therapy since it is available in both synthetic and natural forms over the counter in the United States. But melatonin is not legally sold in Canada, and its use is controversial. Melatonin regulates the body's clock and the way a person responds to light. By doing so, it regulates our cycles of waking and sleeping. Many people use melatonin for insomnia and jet lag, for which studies have shown that it is effective.

Melatonin is also an antioxidant. Antioxidants neutralize oxygen free radicals, the natural by-product of human metabolism, which may be increased in PHAs. Excess free radicals may damage body cells and decrease their ability to resist infection. For details on antioxidants, see A Practical Guide to Nutrition for People Living with HIV, published by CATIE.

Several studies have shown that melatonin may play a useful role, together with chemotherapy, in treating some cancers. However, use of melatonin in AIDS-related cancers has not been studied. Most manufacturers of melatonin say that it is not appropriate for people with cancers that affect immune cells, such as lymphoma and leukemia, because it may promote the growth of these cells. Further, some claim melatonin may increase a person's risk of developing skin cancer because of the way it changes the body's susceptibility to light.
 
In the United States, melatonin is sold in tablets in varying doses. It is probably safer to take synthetic melatonin than natural melatonin, since natural melatonin is produced from the pineal glands of animals, thus has more potential for being contaminated. In most people, melatonin appears to have few side effects. A small percentage of people may have adverse reactions such as headaches, agitation and nausea. Cases of depression have also been reported, although other people use melatonin as an anti-depressant. Pregnant women and children should probably not take melatonin.