Like almost every psychoactive drug it really depends on the individual. I have ME/CFS from a strong genetic propensity to dysautonomia. I think that my ME/CFS

Like almost every psychoactive drug it really depends on the individual. I have ME/CFS from a strong genetic propensity to dysautonomia. I think that my ME/CFS is an autoimmune reaction to the dysautonomia where, counter intuitively, medications like melatonin and amitriptyline, by helping with dysautonomia, actually substantially increase energy levels and mental cognition during the day. My case is a bit extreme at ~1/20K but I think ~1/50 of the general population have a similar but much milder reaction. At N=120 a study like this would not be able to detect that. These ~1/50 people are more likely to have the sort of sleep issues / burnout that makes them more likely to reach for melatonin in the first place. So the more interesting study would be conditioned by the subset of the general population that have already decided they need melatonin.