[Delayed wakefulness-sleep rhythm syndrome and melatonin. Synthesis of existing studies]

Delayed sleep phase syndrome involves undesirable late bed times and arising times with extreme difficulties in falling asleep and in awakening at a desired clock time. These patients present a delayed circadian system. Chronotherapy and phototherapy are designed to have a training effect on the circadian system. Response to these treatments varies widely and depends on the patient's motivation and associated psychological disorders. Other treatments have been proposed with less evident results. The few studies testing the effect of melatonin in delayed sleep phase syndrome concern a small number of patients and present methodological drawbacks. It can be concluded from these studies however that exogenous melatonin influences endogenous secretion more than other secretion rhythms. The effect on sleep time is significant but clinically moderate. More studies are needed to examine the effect of exogenous melatonin as a treatment strategy in delayed sleep phase syndrome.