How big are you? I’m 5’2 and weigh 118. I most assuredly cannot take the same amount of any drug as a larger person. I take many supplements per day and always adjust dosage to my size and weight. 5 mg of melatonin is my max, and usually cut pill in half, which seems to be enough to guarantee a good night’s sleep.
I'm 6'1" and never weigh myself. Maybe 185? I used 3mg nightly for many years, then decided that a little more would help.