Melatonin
Melatonin is a natural chemical that helps you fall and stay asleep. According to the National Sleep Foundation (NSF), it’s only released in the dark, with levels rising just before night. It makes you feel drowsy and maintains high blood melatonin levels for about 12 hours or until daylight. While there’s no "normal" melatonin baseline, the body produces less as we age, and various factors can affect its levels. Melatonin supplements, containing a synthetic version of the hormone, have a sedative effect.
Resources:
Healthline