Melatonin's average benefit belonged to the children in the pool
Pooled across ages, melatonin cut about 7 minutes off falling asleep. Split by age, adults whose insomnia arrives on its own showed nothing significant.
What the study found
Adults with insomnia alone got no clear benefit
Pooled across all ages, melatonin cut about 7 minutes off falling asleep and added about 8 minutes of sleep. Split by age, adults with insomnia alone showed nothing significant, and the whole average belonged to children, teenagers, and insomnia arriving alongside another condition.
The caveat · Two reviews share their trials
The older pooling mixed adults and children without separating them, so its average may be describing the children in it. In the newer one, the adult comorbid group rests on a single study out of 24, and only four of those 24 covered insomnia alongside another condition at all. The two reviews draw on overlapping trials, so they are not independent checks on each other. Neither names which other conditions those four trials covered.
What we don't know
The open question is who melatonin's average benefit belongs to. Pooled across all ages it helped; split by age, adults whose insomnia arrives on its own showed nothing significant, and the benefit looks to belong to children.