zma is basically zinc and magnesium, two minerals that most bodybuilders, if a full blood test with mineral profiling is done, are severely lacking. it doesnt work all that well in developing strength, not nearly as well as victor conte would have you believe. for some, it helps them sleep, for some, it makes them feel like they have a hang over when they wake up. you have to try it yourself. its relatively cheap. i tried it way back in like 2000 and wasnt real impressed. but i have friends that still take it.