Although compelling logic suggests that melatonin may be effective for a variety of disorders, there are few empirical clinical studies. The optimal dose of melatonin is not clear; most studies have used doses that produce supraphysiological blood levels. The timing of melatonin administration is important. Melatonin has few immediate side-effects except drowsiness, but the effects of chronic administration are unclear. Melatonin may be effective in reducing jet lag. In elderly patients with poor sleep and documented low melatonin production, melatonin may be helpful. In several studies, melatonin has been shown to shorten sleep latency. Further studies are needed to clarify the efficacy and safety of melatonin.