A combination of vitamin B6, zinc monomethionine aspartate and magnesium aspartate marketed as a testosterone booster. ZMA initially took the bodybuilding world by storm on the strength of a study showing increased testosterone and IGF-1 levels in collegiate football players. Less impressive results were obtained from a subsequent study, however. The current consensus is that supplemental ZMA (or similar combinations of the relevant nutrients) may be useful for boosting testosterone only in people who are deficient in zinc and/or magnesium.
See the ZMA review for more information.