The best evidence for efficacy is in sleep onset insomnia and delayed sleep phase syndrome. It is most effective when administered 3-5 h before physiological dim light melatonin onset. There is no evidence that extended-release melatonin confers advantage over immediate release. Many children with developmental disorders, such as autism spectrum disorder, attention-deficit/hyperactivity disorder and intellectual disability have sleep disturbance and can benefit from melatonin treatment. Melatonin decreases sleep onset latency and increases total sleep time but does not decrease night awakenings. Decreased CYP 1A2 activity, genetically determined or from concomitant medication, can slow metabolism, with loss of variation in melatonin level and loss of effect. Decreasing the dose can remedy this. Animal work and limited human data suggest that melatonin does not exacerbate seizures and might decrease them. Melatonin has been used successfully in treating headache. Animal work has confirmed a neuroprotective effect of melatonin, suggesting a role in minimising neuronal damage from birth asphyxia; results from human studies are awaited. Melatonin can also be of value in the performance of sleep EEGs and as sedation for brainstem auditory evoked potential assessments. No serious adverse effects of melatonin in humans have been identified.

Previous studies suggested that melatonin improves sleep in insomniac patients with Angelman syndrome. To assess the efficacy of melatonin, a randomized placebo-controlled study was conducted in 8 children with Angelman syndrome with idiopathic chronic insomnia. After a 1-week baseline period, patients received, depending on age, either melatonin 5 or 2.5 mg, or placebo, followed by 4 weeks of open treatment. Parents recorded lights off time, sleep onset time, wake-up time, and epileptic seizures in a diary. Salivary melatonin levels were measured at baseline and the last evening of the fourth treatment week. Melatonin significantly advanced sleep onset by 28 minutes, decreased sleep latency by 32 minutes, increased total sleep time by 56 minutes, reduced the number of nights with wakes from 3.1 to 1.6 nights a week, and increased endogenous salivary melatonin levels. Parents were satisfied with these results. Indications that melatonin dose in Angelman syndrome patients should be low, are discussed.

Recent meta-analyses on melatonin has raised doubts as to whether melatonin is effective in treating sleep problems in people without intellectual disabilities. This is in contrast to results of several trials on melatonin in treating sleep problems in individuals with intellectual disabilities. To investigate the efficacy of melatonin in treating sleep problems in individuals with intellectual disabilities, we performed a meta-analysis of placebo-controlled randomized trials of melatonin in individuals with intellectual disabilities and sleep problems. Data were selected from articles published on PubMed, Medline, and Embase between January 1990 and July 2008. We examined the influence of melatonin on sleep latency, total sleep time, and number of wakes per night. Quality of trials was assessed using the Downs and Black checklist. Nine studies (including a total of 183 individuals with intellectual disabilities) showed that melatonin treatment decreased sleep latency by a mean of 34 minutes (p<0.001), increased total sleep time by a mean of 50 minutes (p<0.001), and significantly decreased the number of wakes per night (p<0.05). Melatonin decreases sleep latency and number of wakes per night, and increases total sleep time in individuals with intellectual disabilities.

Melatonin treatment improves some aspects of chronic sleep disturbance in individuals with ID.