Ramelteon is a melatonin receptor agonist with affinity for the human melatonin receptor subtype 1, melatonin receptor subtype 2 and selectivity over the melatonin receptor subtype 3 receptor. It also demonstrates agonist activity in vitro relative to melatonin in cells expressing human melatonin receptor subtype 1 or melatonin receptor subtype 2 receptors. The binding of melatonin at these receptors is thought to contribute to maintenance of the circadian rhythm underlying the normal sleep-wake cycle.