I have been using melatonin from time to time since about 2 years. As far as I remember, 1,5 mg was enough for me to feel sleeppy. Recently I took 3 mg pill, with bare effect. Two days ago i took 6 mg, and still I had problems to fall asleep. The previous night I decided to experiment and took 12 mg, and what was suprising to me, I felt boozed with energy rather than being sleeppy. I felt asleep after 3 hours of laying in bed and woke up rather not rested. I felt like my mind was working for all the night without turning off. Thus, those three hours without sleep were very interesting, a deeper insight into self was present.