Introduction and objective: Melatonin is the most important compound produced by the pineal gland. Its daily secretion cycle is responsible for the normal rhythm of sleep and wakefulness. The aim of the study was to analyse the clinical application of melatonin and melatonin receptor agonists MT1 and MT2 in the treatment of sleep disorders and depression. Review methods: A literature review was performed by searching electronic databases, such as PubMed, Scopus, Google Scholar, Web of Science, entering key words ‘melatonin’, ‘ramelteon’, ‘tasimelteon’, ‘sleep disorders’ in Polish and English. Brief description of the state of knowledge: The action of melatonin is determined by its agonistic effect on the melatonin receptors MT1 and MT2. Darkness stimulates the synthesis of this hormone, and the suprachiasmatic nuclei of the hypothalamus (SCN) are responsible for regulation of melatonin secretion. The appearance of melatonin production disorders is a phenomenon observed most frequently in elderly people, the blind, those undertaking shift work or travelling intercontinentally. In addition to melatonin, other MT1 and MT2 receptor agonists such as ramelteon, tasimelteon or agomelatine are used in the treatment of sleep disorders. However, the latter is used primarily as an antidepressant, due to its additional antagonistic effect on serotonin 5-HT2C receptors. Summary: Abnormalities of melatonin secretion can lead to sleep disorders, as well as other conditions throughout the body. Melatonin receptor agonists are recognised as relatively well tolerated and safe, and their use may be considered in a wide range of patients.