.5mg melatonin isn't enough to feel anything. Between 3-6mg is what you need to notice anything. I've tried quite a few sleep aids, and as far as OTC supplements go, without resorting to prescription things like ambien and what not, the only one that worked for me was need2sleep. I take it as a staple supplement, I use it 5 days on, and 2 days off. Basically I just take the weekends off of it and take something else on the weekends, and then go back to it throughout the week.
Need to Sleep