<p>Ramelteon is a melatonin receptor agonist with both high affinity for melatonin MT1&nbsp;and MT2receptors, and lower selectivity for the MT3&nbsp;receptor. Melatonin production is concurrent with nocturnal sleep, meaning that an increase in melatonin levels is related to the onset of self-reported sleepiness and an increase in sleep propensity. MT1&nbsp;receptors are believed to be responsible for regulation of sleepiness and facilitation of sleep onset, and MT2&nbsp;receptors are believed to mediate phase-shifting effects of melatonin on the circadian rhythm. While MT1&nbsp;and MT2&nbsp;receptors are associated with the sleep-wake cycle, MT3&nbsp;has a completely different profile, and therefore is not likely to be involved in the sleep-wake cycle. Remelteon has no appreciable affinity for the gamma-aminobutyric acid (GABA) receptor complex or receptors that bind neuropeptides, cytokines, serotonin, dopamine, norepinephrine, acetylcholine, or opiates.</p>