hormone secreted by the pineal gland
"The doctor explained that our bodies naturally produce melatonin, a hormone secreted by the pineal gland, to help regulate sleep cycles at night."
A hormone, related to serotonin, that is secreted by the pineal gland, and stimulates colour change in the skin of reptiles, and is involved in the sleep/wake and reproductive cycles in mammals.
"After reading about how melatonin regulates both our sleep patterns and seasonal breeding behaviors, I decided to take a supplement before bed to help adjust my circadian rhythm during winter months."