A hormone produced by the pineal gland. The level of melatonin increases at night, but like other hormones, production of melatonin diminishes with age. In recent times, melatonin has become available as a drug and a dietary supplement. It appears to have some use against insomnia, jet lag, and circadian misalignment. Melatonin is a powerful antioxidant which can easily cross cell membranes including the blood-brain barrier. It has been studied for the treatment of cancer, immune disorders, cardiovascular diseases, depression, seasonal affective disorder, and sexual dysfunction; the results of most of these studies remain inconclusive. However, it has been shown to clearly ameliorate seasonal affective disorder and circadian misalignment, in studies by Alfred J. Lewy (OHSU) and other researchers.