What is melatonin? And how does it function? Melatonin is a kind of hormone that is produced by your brain when exposed to darkness and can be produced naturally in your body. Its main function is to regulate the timing of your circadian rhythms (24-hour internal clock) and sleep. It is produced in the pineal gland in your brain. It can also be found in different parts of … [Read more...] about Melatonin: What is the Side Effects and Precautions?