Melatonin is a hormone that tells the body it's time to sleep. In people without sleep problems, the body follows a roughly 24-hour biological clock called the circadian rhythm.

The main time for melatonin synthesis is from 2 am to 3 am, and light shining on the retina will destroy the formation of melatonin, affect the normal neuroendocrine rhythm, and inhibit the secretion of melatonin from the pineal gland. Therefore, when flying around the world, people who need jet lag, night shift workers, and people exposed to artificial light sources at night can take melatonin for a short period of time.

Melatonin is a hormone synthesized by the pineal gland using tryptophan. Its most well-known function is to improve sleep. Melatonin secreted by pineal gland shows a strong physiological cycle law, which is related to the alternation of day and night. It secretes less during the day and more at night. One is people who need jet lag and shift work.