Melatonin is a hormone that anticipates the daily onset of darkness.

• It is involved in the entrainment (synchronization) of the cicardian rhythms of physiological functions, including sleep timing, BP regulation, seasonal reproduction, and many others
• Many of melatonin's biological effects are produced through activation of melatonin receptors, while others are due to its role as a pervasive and powerful antioxidant, with a particular role in the protection of nuclear and mitochondrial DNA
• It can be taken orally, liquid form, capsules, tablets, subliningually, or transdermal
• There is immediate or prolonged release form

• Sleep aid
• Tx of some sleep disorders

• It is sold OTC in the USA and Canada, in other countries it may require prescription or be unavailable