There was a MIT study that the optimal doaage for sleep is around 300mcg. The body produces about 30mcg of melatonin afik, and the oral bioavailability of mel

There was a MIT study that the optimal doaage for sleep is around 300mcg. The body produces about 30mcg of melatonin afik, and the oral bioavailability of melatonin is about 10% so, the math works out. More might produce excessive grogginess after you wake up, and in my experience it leads to fast tolerance -- so it doesn't work; 300-450mcg works in perpetuity for me.