Melatonin also known as sleep hormone is produced by the pineal gland located in the brain. Melatonin is a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles. As a dietary supplement, it is often used for the short-term treatment of sleep onset insomnia and insomnia related to altered sleep schedule e.g., jet lag, shift work.
Ferracioli-Oda, E., Qawasmi, A., & Bloch, M. H. (2013). Meta-analysis: melatonin for the treatment of primary sleep disorders. PloS one, 8(5), e63773. https://doi.org/10.1371/journal.pone.0063773
Tordjman, S., Chokron, S., Delorme, R., Charrier, A., Bellissant, E., Jaafari, N., & Fougerou, C. (2017). Melatonin: Pharmacology, Functions and Therapeutic Benefits. Current neuropharmacology, 15(3), 434–443. https://doi.org/10.2174/1570159X14666161228122115
Costello, R. B., Lentino, C. V., Boyd, C. C., O'Connell, M. L., Crawford, C. C., Sprengel, M. L., & Deuster, P. A. (2014). The effectiveness of melatonin for promoting healthy sleep: a rapid evidence assessment of the literature. Nutrition journal, 13, 106. https://doi.org/10.1186/1475-2891-13-106