Summary of possible benefits and harms

Three small studies have looked at how well melatonin works for treating sleep disorders in children aged 6 to 14 years with ADHD. Taken together, only 124 children and young people were involved, including only 19 children and young people in the smallest study. Importantly, children in these studies were given unlicensed melatonin. None of these studies used off-label prolonged-release melatonin and none of them took place in the UK. Other studies have looked at melatonin in other groups, such as children with neurodevelopmental disorders, but these are less relevant to children with ADHD.

All children who took part in the studies had been diagnosed with ADHD and also problems falling asleep. In 2 of these studies, children took either unlicensed melatonin or placebo (a dummy treatment) every night before bedtime for a period of between 10 days and 4 weeks to see if it could help them fall asleep. A third study monitored the children who had taken part in the largest of the studies (mentioned above) for around 3 and a half years to see whether it is safe to take melatonin for this longer period. Most children did not take melatonin for the whole 3 and a half years; on average, children took melatonin for 18 months.

How well does melatonin work?

This small amount of evidence indicated that taking unlicensed melatonin just before bedtime reduced the time it took the children to fall asleep (after lights out or when they were put to bed) by approximately 20 minutes. It also improved the total time they were asleep by an average of approximately 15 to 20 minutes.

The effect of melatonin in the medium to long term is uncertain because the studies have not accurately assessed how well melatonin works by comparing it with placebo (a dummy treatment) beyond 4 weeks. The longer study (mentioned above) did not include any children and young people taking placebo.

It is important to note that there was no good quality evidence showing that melatonin improves the behaviour or mental function of children or young people with ADHD, or their quality of life. However, parental satisfaction with melatonin was high, with 87.8% of parents expressing the opinion that "melatonin is an effective therapy for the sleep onset problems of my child", 70.8% that "melatonin improved daytime behaviour of my child" and 60.9% that "melatonin improved the mood of my child". These were the views of a group of 94 parents whose children continued taking melatonin for different time periods after they had taken part in 1 of the studies that looked at how well it worked. They may not represent the views of all parents of children who have tried using melatonin.

One of the studies indicated that the improvements in sleep experienced through taking melatonin may be lost if the medication is stopped.

However, the melatonin products used in these studies are unlicensed in the UK which means that they are not subject to the same high-quality effectiveness and safety standards as licensed medicines. Therefore, how well different unlicensed melatonin products work and how safe they are may vary depending on which 1 is used. Also these small studies were done in the Netherlands and Canada and so their findings may not apply to UK children and young people with ADHD.

What are the possible harms or side effects?

The number of side effects, and how severe they were, was found to be similar between children given placebo (a dummy treatment) and those given melatonin in the studies. However, the studies were small, which may mean that they could have missed differences in side effects between the groups. The most common side effects reported in those given melatonin in the larger of the studies were headache, hyperactivity, dizziness and abdominal pain (each of these side effects were reported for about 2 or 3 children out of 105; note 1 child could have more than one side effect). There were no reports of melatonin causing serious side effects in the studies.

Based on these small studies, unlicensed melatonin appeared relatively safe in the short term (using it for up to 4 weeks) and medium term (using it for up to 18 months). However, all the studies were small so infrequent side effects may not have been detected; the safety of long term melatonin use in children and young people with ADHD is unclear.

Please note that the results of the research studies only indicate the benefits and harms for the population in the studies. It is not possible to predict what the benefits and harms will be for an individual patient being treated with melatonin.