ZMA, a nutritional supplement, is lauded by bodybuilders to increase muscle mass (and decrease muscle breakdown), increase strength, facilitate restful sleep, boost immune function, and even increase testosterone levels. However, scientific research does not actually support all of those claims. Also, ZMA carries dangers—it interacts with medications and can lead to a fatal overdose in rare cases. Read on to learn more about ZMA, its benefits, side effects, and potential dangers.
What Is ZMA?
Zinc is a trace element, meaning it is only needed in small amounts in the body but is essential for humans. Magnesium is an important macroelement (needed in relatively large amounts). Vitamin B6 is a water-soluble compound used for a variety of functions in the body and possibly increases the effect of zinc and magnesium [2, 3, 4].
Many have claimed that ZMA is necessary for bodybuilding and exercise because some evidence suggests that athletes are deficient in zinc and magnesium due to increased exertion. However, other studies found the opposite to be true, while a review found mixed results [5, 6, 7, 8, 9, 10, 11, 1, 12, 13, 14].
How ZMA Works
As ZMA is a nutritional supplement, it works by providing the body with adequate levels (or excess levels) of zinc, magnesium, and vitamin B6 for proper functioning. As the body does not store zinc, it must be replenished via diet. ZMA contains about 3 times the recommended daily dose of zinc (ZMA contains 30 mg) [18, 1, 19].
Magnesium is a macroelement (meaning the body requires relatively high levels of it) that is involved in over 300 different cellular processes. ZMA contains the recommended daily dose of magnesium for adult men. It also contains a much-larger-than-recommended daily dose of vitamin B6, about 10 times more (11 mg) [18, 1, 20, 21].
While some claim that this ratio in ZMA is important for its action, there are no studies to support the claims.
Health Benefits of ZMA
We base most of the health benefits of ZMA solely on comparable studies about each of its components, due to lack of other data. Studies with ZMA exist only for the first 2 benefits listed.
1) May Enhance Athletic Performance and Strength
Interestingly, one of the few studies that tested the effects of all 3 components as the ZMA supplement saw there were no significant changes in hormones (anabolic or catabolic), body composition, bench press and leg press, upper- or lower-body muscular endurance, or cycling breathing performance in 42 trained men .
All other studies were performed with the individual components, and point to the fact that more research and larger samples may need to pick up the effect. However, we conclude that research is lacking support for the use of ZMA for improving athletic performance and strength. Several studies have examined the effect of zinc and magnesium on these parameters, as described below.
In a study with 23 triathletes, magnesium supplementation increased swimming, cycling, and running speed. Zinc levels in the blood were correlated with increased athletic performance in 21 football players (as measured by an exercise test on a cyclo-ergometer machine and blood lactate levels) [22, 23].
A study with 30 healthy adults found that magnesium supplementation and martial arts together increased 2 types of red blood cells, which may help with athletic performance. This same effect was seen with zinc [24, 25, 26].
In a study with 26 healthy untrained adults, magnesium supplementation greatly increased strength. Another study of 8 healthy men showed low zinc decreases knee and shoulder muscle capacity. Zinc supplementation increased strength in a study of 16 healthy women (DB) [27, 28, 29].
2) May Boost Testosterone Levels
One study found ZMA supplementation increased testosterone levels of 27 healthy football players without nutritional deficiencies .
However, ZMA supplementation (30 mg zinc, 450 mg magnesium, and 11 mg vitamin B6) did not affect testosterone levels in the blood of 14 healthy men without nutritional deficiencies. Another study with ZMA found no significant changes in hormones in 42 healthy trained men [31, 1].
Zinc deficiency resulted in lower levels of testosterone in the blood in rats. The rats fed a zinc-deficient diet were also more sensitive to estrogen (more receptors for female sex hormones) and less to androgens (fewer receptors for male sex hormones) [32, 33].
3) May Improve ADHD
Supplemental levels of zinc (15 mg, twice a day) improved response to ADHD medication in children (52 participants). In another study of children with ADHD, zinc (150 mg/day) improved hyperactive, impulsive, and impaired-socialization symptoms but had no effect on attention deficit symptoms (400 participants) [35, 36].
A large study found that magnesium, zinc, and polyunsaturated fatty acids (5 mg zinc and 80 mg magnesium) curbed both attention deficit and hyperactivity issues in 810 children. The combination of magnesium with vitamin B6 (6 mg per kg/day magnesium and 0.6 mg per kg/day vitamin B6) was also very effective in curbing ADHD issues in children (study with 76 children) [37, 3].
4) May Boost Immunity
In a study with 153 children, treatment with zinc (10 mg/twice a day) shortened the duration of fever in boys (but not girls) with a severe lower respiratory infection. Zinc supplementation (10 mg/day) also reduced the frequency of respiratory infections over a period of 6 months in a study with 609 children [38, 39].
Similarly, zinc nasal spray reduced common cold symptom severity (nasal drainage, nasal congestion, hoarseness, and sore throat) and illness duration in a study with 80 adults .
A review study on micronutrients identified zinc and vitamin B6 (among a few other nutrients) as important to immune function. This may justify the combination of ZMA .
A vitamin B6 deficiency slowed white blood cell production in mice, pointing to its role in maintaining a healthy immune system .
5) May Alleviate Stress
Magnesium supplementation prevented increases in the stress hormone, cortisol, and in another hormone, aldosterone, following exercise in nine healthy men. Similarly, zinc given to medical students reduced the release of the stress hormone, cortisol. In a study with 54 individuals, those with anxiety had lower levels of zinc in their blood compared to controls [43, 44, 16].
In a study with 23 triathletes, magnesium supplementation lowered serum cortisol levels, a measurement of stress .
A vitamin B-specific multivitamin that contains magnesium (140 mg magnesium phosphate, 75 mg B1, 10 mg B2, 68.7 mg B5, 25 mg B6, and 30 ug B12) reduced stress levels and increased mood in 60 healthy adult workers .
These studies may justify the combination in ZMA, but more evidence is needed.
6) Reduces Exercise-Induced Fatigue
Zinc prevented exercise-induced fatigue (measured as a drop in thyroid hormone and testosterone levels) in a study of 10 sedentary men. The same result was seen in 10 male wrestlers. Similarly, magnesium supplementation prevented a drop in TSH levels triggered by exhaustion during martial arts training [46, 47, 48].
Limitations and Caveats
While there are quite a few studies of the effects of both zinc and magnesium on humans, there is not much data on zinc, magnesium, and vitamin B6 together.
The main paper referenced by many bodybuilding sources claims that ZMA increased testosterone levels and strength in a study with 27 football players. However, one of the authors owns the company that makes the specific ZMA formulation. The same company funded the research, as stated in the “Disclosure of Commercial Interests” section within the attached reference .
Side Effects & Precautions
An excess dose of zinc can cause nausea, vomiting, stomach pain, sluggishness (lethargy), and extreme tiredness (fatigue). Even taking a non-toxic dose of 100 to 300 mg of zinc a day can cause a copper deficiency (with symptoms of low red blood cell levels (anemia), low white blood cells level (neutropenia), and reduced immune function. It can also negatively affect the ratio of good and bad cholesterol (low-density-lipoprotein to high-density-lipoprotein) .
Supplemental zinc intake of over 100 mg/day and consistent zinc supplementation for more than 10 years were both correlated with an increased risk of prostate cancer in men .
Similarly, though it is rare, it is possible to overdose on magnesium (hypermagnesemia), which can cause abdominal cramping, diarrhea, and nausea. Extremely high doses of magnesium (magnesium toxicity) can be fatal [53, 54, 50, 51].
ZMA can interact with a variety of other drugs and other supplements because it is composed of zinc, magnesium, and vitamin B6.
- Antibiotics: Quinolone and tetracycline antibiotics interact with zinc in the stomach and intestines and prevent the body from absorbing both zinc and the antibiotic
- Penicillamine: Zinc interacts with penicillamine, preventing the body from absorbing it
- Diuretics: Thiazide diuretics cause the body to evacuate zinc in urine
- Bisphosphonates used for the treatment of osteoporosis: Magnesium prevents the body from absorbing this drug
- Antibiotics: Tetracyclines and quinolone antibiotics can form complexes with magnesium
- Diuretics: Loop, thiazide, and ethacrynic acid diuretics cause the body to evacuate magnesium in urine while potassium-sparing diuretics do the opposite
- Proton pump inhibitors, used for acid reflux (GERD): PPIs taken for over a year can cause magnesium deficiency but the exact mechanism is not known
- Cycloserine: This antibiotic causes the body to evacuate vitamin B6 in urine
- Anti-seizure medications: Valproic acid, carbamazepine, and phenytoin cause the body to break down vitamin B6, resulting in a deficiency
- Theophylline: This drug causes a vitamin B6 deficiency, though the mechanism is unknown
Supplementing With ZMA
ZMA supplements are widely available, almost exclusively in pill form, but are also found in powder form. ZMA is available by itself or mixed with other substances meant to encourage muscle development and recovery or improved sleep, such as theanine and 5-HTP (5-Hydroxytryptophan).
- 30 mg zinc monomethionine aspartate
- 450 mg magnesium aspartate
- 11 mg vitamin B6
One user reported a combination of ZMA and melatonin greatly improved sleep quality. Similarly, another user said it helped his muscles relax for better sleep. A third user said it improved sleep duration.
A few users didn’t see any results.
One user said it improved their migraines and attributed it to the magnesium.