Supplement analysis backed by scientific evidence · PT

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Limited evidencePhysical performance

ZMA

ZMA is zinc, magnesium and B6 in a branded ratio, sold on the promise of higher testosterone and better sleep. Controlled trials in resistance-trained men found no effect on hormones, strength or body composition, and the sleep evidence is weak too; it is only useful if you are actually deficient.

What the science says

  • Raising testosterone or IGF-1 Limited evidence

    The independent replication attempt is negative: resistance-trained men took ZMA or placebo for 8 weeks alongside training, and there were no differences in total or free testosterone, IGF-1, cortisol, strength, or body composition. The frequently cited positive study in football players was small, manufacturer-affiliated, and has never been reproduced.

  • Improving sleep quality Limited evidence

    A 2024 randomised trial gave zinc magnesium aspartate to men across two consecutive nights of partial sleep deprivation and found no meaningful improvement in sleep quality or in next-day submaximal weightlifting performance. Magnesium alone has better, though still modest, sleep evidence than the ZMA combination.

  • Correcting genuine zinc or magnesium shortfall Moderate evidence

    If you are actually low in zinc or magnesium (plausible in heavy sweaters, restricted-calorie dieters, or vegetarians with high phytate intake), correcting that deficit does restore normal testosterone and neuromuscular function. That is a deficiency correction rather than an ergogenic effect, and it does not require the branded ZMA form.

Dosage & safety

Studied doseThe standard formula is 30 mg zinc (as monomethionine/aspartate), 450 mg magnesium aspartate, and 10.5 mg vitamin B6, taken 30-60 minutes before bed on an empty stomach. Note that 30 mg zinc is already close to the 40 mg/day tolerable upper intake level once dietary zinc is added.
SafetyChronic zinc at 30+ mg/day risks copper deficiency, which can cause anaemia and neurological problems, so do not take indefinitely without accounting for total intake. Zinc on an empty stomach commonly causes nausea. Magnesium aspartate can cause loose stools. Zinc impairs absorption of tetracycline and quinolone antibiotics and of penicillamine; separate doses by 2-4 hours. Not prohibited in sport, though testosterone-marketed products have a poor contamination record generally.

Scientific references

Where to buy

JYM Supplement Science, ZMA®, Zinc & Magnesium, 90 Vegetarian Capsules

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