Yael, From wikopedia
The proportion of ingredients generally used in products is 20-30 mg Zinc, 400-500 mg Magnesium and ~10mg B6. This supplement should never be taken with calcium, as calcium blocks the absorption of zinc. Any ZMA supplement that has calcium in it should be avoided. ZMA should also be taken before bed on an empty stomach (2 hours after eating your last meal and at least 30 minutes prior to any other supplements).