Chronic sleep onset insomnia (CSOI) is frequently reported in children with attention-deficit/hyperactivity disorder (ADHD) with rates up to 28% in medication free children with ADHD. In the general child population, insomnia is associated with daytime fatigue, impaired daytime functioning and impaired health status. A recent study demonstrated that children with ADHD and CSOI showed a delayed sleep-wake rhythm with normal sleep maintenance as well as a delayed increase of endogenous melatonin in the evening. Properly timed exogenous melatonin in the afternoon or evening advances endogenous melatonin secretion in the evening, facilitating sleep onset at an earlier time. Short-term melatonin treatment, i.e. several weeks, has proven to be safe and effective for the treatment of CSOI in children with ADHD. The number of clinical trials on melatonin treatment in children with insomnia increases, and with that the evidence for its efficacy and safety in the short-term. However, there is limited information available on the long-term effectiveness and safety of melatonin therapy. Most studies assessing effectiveness and safety of exogenous melatonin therapy in children included a short follow-up duration of several weeks. Only few studies included a longer follow-up time, but the numbers of participants were small.

Recently, one study assessed prospectively long-term effectiveness and safety of melatonin treatment in children with neuro-developmental disabilities. Mean follow-up duration was 3.8 yr. Effectiveness of long-term melatonin therapy was rated by the caregivers as highly positive. Adverse reactions were not found.

The results of the study, however, relate to a heterogeneous group of children with multiple neuro-developmental disabilities and may not be applicable to the general child population or other clinical populations such as children with ADHD. Furthermore, several clinically relevant questions on melatonin treatment remained unanswered, such as the degree of relapse of sleep onset insomnia after stopping melatonin and the long-term effects of melatonin treatment on sleep improvements, behaviour and mood in children with ADHD.

The long-term use of exogenous melatonin did not show safety concerns in children regarding serious adverse events and treatment related co-morbidity. Melatonin remains an effective therapy on the long-term for the treatment of sleep onset insomnia in children with ADHD, however, it does not provide a permanent cure. Even after several years of treatment, discontinuation of melatonin treatment often leads to a relapse of sleep onset insomnia and to resuming melatonin treatment.