I went to a conference about sleep difficulties in children a while back.
It was interesting the data that had 'accidentally' come out from their studies (hadn't been what they started to look at, at all), relating to children and teens behaviour, and their sleep patterns.
They said that it had always been assumed by them (I I think fair to say, most of us) that dc with ADHD, and other disorders didn't sleep well because of the ADHD, but [and they said a lot more research would need to be done on this - they were early findings] through working on the project they were doing, they were now looking at a hypothesis that it was the other way round, and that the lack of quality sleep in both young dc and in teens, was the cause of the prolonged and more challenging behaviour in the day, rather than the other way round.
Plus, there was the added thought that, when parents aren't getting any sleep themselves, then their patience is stretched to the limit, and they don't cope so well with challenging behaviour in the day, whereas, once the parents began to get half way back towards normality, they were much better equipped to cope with challenging behviour when it arose, and it then didn't escalate as much.
So lots of interesting research to be done (sorry - interesting to me, possibly you are too tired at the moment to have the capacity to take much notice. Lack of sleep is a killer
).
However, sorry, I'm not medical and don't know much about longer term effects of Melotonin.