insomnia
"I've been taking Melatonin for a few months now, for delayed sleep phase syndrome and it has helped with sleep dramatically about half of the time. The rest of the time, I still usually get to sleep at my "normal" time around 2:30-3:30am. The problem with this is it's unreliable. You never know when it'll work and when it won't. And there are times when it just doesn't. I will keep taking it though."