Plus...
Does zma shrink your testicals like steroids do?
No, absolutely not.
Anabolic Steroids are exogenous hormones that you are adding to the body artificially. Your body is not dumb and notices the massive increase and tries to fight the imbalance by shutting down your natural testosterone production. When this happens your testicles begin to atrophy, just as your arm muscles shrink if you stop lifting weights with them.
ZMA on the other hand works to increase your NATURAL testosterone. The "accepted" way that it is supposed to work is by providing your body with Vitamin B6, Zinc, and Magnesium. These are essential to the body for lots of functions to occour, including testosterone production.
Another thing that people don't seem to mention much about ZMA is that zinc is an aromatase inhibitor as well. Aromatase is an enzyme which breaks down testosterone into estrogen in the male body. By inhibiting this enzyme you will see increases in free testostrone levels. This is presumably another method of action.
If anything, increased natural testosterone production is going to make your testicals GROW, not shrink.