Melatonin

Melatonin, chemically N-acetyl-5-methoxy tryptamine,[1] is a substance found in animals, plants, fungi, and bacteria. In animals, it is a hormone that anticipates the daily onset of darkness;[2] however in other organisms, it may have different functions. Likewise, the synthesis of melatonin in animals differs from that in other organisms.

In animals, melatonin is involved in the entrainment (synchronization) of the circadian rhythms of physiological functions including sleep timing, blood pressure regulation, seasonal reproduction, and many others.[3] Many of melatonin's biological effects in animals are produced through activation of melatonin receptors,[4] while others are due to its role as a pervasive and powerful antioxidant,[5] with a particular role in the protection of nuclear and mitochondrial DNA.[6]

https://en.wikipedia.org/wiki/Melatonin