This topic has been a hotbed of controversy in other forums.
The objective is to induce growth hormone release and test production over night.
The problem: test production follows diurnal patterns and the release rate is highest, along with other hormones in the morning hours. Pushing the HPA axis can have consequences on adrenaline, epinephrine, and melantonin production.
Chiefly, in some who already have sufficient levels of epinephrine and test, it boosts body temperature, and this and an increase in brain activity (with epinephrine release) can keep the mind churning and stops the body from slowing down (dropping in thermal output, a trigger for REM sleep).
This busy mind problem, along with the push pull production of adrenaline at higher receptor uptake of epinephrine in the cortex and hypothalamus, leads to dreaming and lighter, and interrupted sleep episodes.
Some users of ZMA therefore report poor sleep, with heavy dreaming and morning tiredness.
Others, not as sensitive to zinc and more responsive to magnesium (necessary for deeper sleep), report little or no problems and in often improved sleep quality from use of ZMA.
The effect on you, as an individual, will vary, according to your neurotransmitter receptor function, HPA function, your response to zinc and magnesium (absorption as well as use of other dietary sources of these two supps), age, sleep habits, stress levels, and the phase of the moon (sort just kidding..athough it can affect your sensitivity to light contamination in your bedroom at night).
In short - try it, at lower than recommended doses first. If you have no problems, cautiously increase the dosage.
I also recommend use of the herb valarian as a nonhabit forming, non acclamating sleep aide. It works.
Hope this answsers your question.