The only hormone secreted into the bloodstream by the pineal gland. The hormone appears to inhibit numerous endocrine functions, including the gonadotropic hormones. Research exists on the efficacy of melatonin in treating jet lag and certain sleep disorders. Dosages greater than l milligram have been associated with drowsiness, headaches, disturbances in sleep/wake cycles and is contraindicated in those who are on antidepressive medication. It also negatively influences insulin utilization.