It is claimed to increase testosterone levels, but there is no evidence to suggest that this occurs in healthy men. Though men with zinc deficiencies can supplement zinc to fix their deficiency and increase their testosterone levels, there is no evidence to suggest this occurs in men with no deficiency.
Aspartate has also been claimed to increase testosterone, but it is in too low of a dose in ZMA to have any effect on testosterone.
Despite ZMA’s lack of effect on testosterone levels, it can be a useful supplement for people that lack zinc and magnesium.
It is possible that ZMA can cause weird dreams, and the anecdotes support this; however, since this has not been directly investigated the best 'proof' that can be given is weak.
This claim has not been investigated much, but a pilot study suggests that a dose of 250mg pyridoxine can alter dream perception in college aged men, through a hypothesized increased conversion of tryptophan to serotonin. This dose of B6, however, is much higher than that occurring in ZMA products; which tends to range in the 10-50mg range and usually at the lower end.
One other study has reported synergism between B6 and Magnesium in regards to anxiety reduction, when the subjects were women experiencing PMS; it is theoretically possible that the ZMA formulation enhances the actions of pyridoxine allowing the previous research's results to be relevant.