<unk>  sold under the brand name Circadin among others, is a dietary supplement and medication as well as naturally occurring hormone. As a hormone,<unk> is released by the pineal gland and is involved in sleep–wake cycles. As a supplement, it is often used for the short-term treatment of insomnia, such as from jet lag or shift work, and is typically taken orally. Evidence of its benefit for this use, however, is not strong. A 2017 review found that sleep onset occurred six minutes faster with use, but found no change in total time asleep. A prolonged-release form of<unk> is also approved for use as a medication in Europe for the treatment of insomnia in certain people. Side effects from<unk> supplements are minimal at low doses for short durations. Side effects of<unk> are rare but may occur in 1 to 10 patients in 1,000. They may include somnolence (sleepiness), headaches, nausea, diarrhea, abnormal dreams, irritability, nervousness, restlessness, insomnia, anxiety, migraine, lethargy, psychomotor hyperactivity, dizziness, hypertension, abdominal pain, heartburn, mouth ulcers, dry mouth, hyperbilirubinaemia, dermatitis, night sweats, pruritus, rash, dry skin, pain in the extremities, symptoms of menopause, chest pain, glycosuria (sugar in the urine), proteinuria (protein in the urine), abnormal liver function tests, increased weight, tiredness, mood swings, aggression and feeling hungover. Its use is not recommended during pregnancy or breastfeeding or for those with liver disease.<unk> acts as an agonist of the<unk> MT1 and MT2 receptors, the biological targets of endogenous<unk>  It is thought to activate these receptors in the suprachiasmatic nucleus of the hypothalamus in the brain to regulate the circadian clock and sleep–wake cycles. Immediate-release<unk> has a short elimination half-life of about 20 to 50minutes. Prolonged-release<unk> used as a medication has a half-life of 3.5 to 4hours.<unk> was discovered in 1958. It is sold over the counter in Canada and the United States; in the United Kingdom, it is a prescription-only medication. In Australia and the European Union, it is indicated for difficulty sleeping in people over the age of 54. In the European Union, it is indicated for the treatment of insomnia in children and adolescents. The US Food and Drug Administration (FDA) treats<unk> as a dietary supplement and as such has not approved it for any medical uses. It was approved for medical use in the European Union in 2007. Besides<unk>  certain synthetic<unk> receptor agonists like ramelteon, tasimelteon, and agomelatine are also used in medicine.
Melatonin 
Etoperidone
Sertindole
Tropisetron
Zolpidem
Cilansetron
Chloracyzine
Alosetron