Ramelteon is a selective, high a- nity agonist of melatonin MT1 and MT2 receptors, recently approved by FDA for the treatment of insomnia characterized by di culty with sleep onset. Ramelteon promotes sleep by regulating the sleep/wake rhythm through its action on melatonin receptors in the suprachiasmatic nuclei of the hypothalamus (a site of the central circadian pacemaker). The drug has no appreciable a nity for a large number of receptors, ion channels, transporters, and no e ect on the activity of numerous enzymes. Ramelteon has been demonstrated to reduce latency to persistent sleep and increase total sleep time, with no next-morning residual e ects, rebound insomnia or withdrawal symptoms upon discontinuation. The drug did not alter sleep architecture. The most commonly reported adverse e ects of ramelteon were mild to moderate, and include headache, somnolence and sore throat.Keywords: ramelteon, melatonin, melatonin receptors, circadian rhythms, insomnia, chronobiological sleep disorders.