<unk>  is a hormone primarily released by the pineal gland at night, and has long been associated with control of the sleep–wake cycle. In vertebrates,<unk>  is involved in synchronizing circadian rhythms, including sleep–wake timing and blood pressure regulation, and in control of seasonal rhythmicity including reproduction, fattening, moulting and hibernation. Many of its effects are through activation of the<unk>  receptors, while others are due to its role as an antioxidant. In plants, it functions to defend against oxidative stress. It is also present in various foods.<unk>  was discovered in 1958. In addition to its role as a natural hormone,<unk>  is used as a dietary supplement and medication in the treatment of sleep disorders such as insomnia and circadian rhythm sleep disorders; for information on<unk>  as a supplement and medication, see the<unk>  (supplement/medication) article.
Melatonin
Etoperidone
Sertindole
Tropisetron
Zolpidem
Cilansetron
Chloracyzine
Alosetron