melatonin is normally produced by the body's pineal gland. as we get older, we do not produce as much melatonin. the pineal gland is part of the endocrine system and therefore produces a hormone (as does the pancreas produce insulin...the adrenal glands produce adrenaline....ect)
melatonin is also a very powerful antioxidant. i have actually seen people buy large stores of it to combat the anthrax spore (god forbid that we are ever exposed). i would certainly never take more than 6mgs/night....you really shouldn't have to. sometimes less is more ya know? whenever i take more than 25mgs of benadryl, i am restless, but just 25 mgs puts me to sleep pretty quick.
ps. never give melatonin to a child
not that you would, just so ya'll know...