People with circadian rhythm sleep disorders may use oral melatonin to help entrain (biologically synchronize in the correct phase) to the environmental light-dark cycle. Melatonin reduces sleep onset latency to a greater extent in people with delayed sleep phase disorder than in people with insomnia.[11]
Melatonin has been studied for insomnia in the elderly.[12][13][14] Prolonged-release melatonin has shown good results in treating insomnia in older adults.[15] Short-term treatment (up to three months) of prolonged-release melatonin was found to be effective and safe in improving sleep latency, sleep quality, and daytime alertness.[16]
Evidence for use of melatonin as a treatment for insomnia is, as of 2015, insufficient;[7] low-quality evidence indicates it may speed the onset of sleep by 6 minutes.[7] A 2004 review found "no evidence that melatonin had an effect on sleep onset latency or sleep efficiency" in shift work or jet lag, while it did decrease sleep onset latency in people with a primary sleep disorder and it increased sleep efficiency in people with a secondary sleep disorder.[11] A later review[17] found minimal evidence for efficacy in shift work.