ZMA is becoming increasingly popular as a testosterone and muscle building supplement. But what harm is doing to your body? Let’s examine ZMA side effects by going through each ingredient: zinc, magnesium aspartate, and vitamin B6.
Zinc Side Effects
In studies examining zinc’s effects on the common the cold there are reports of unpleasant taste, abdominal cramping, and taste distortion.  Other common zinc side effects include:
- Reduced HDL cholesterol
Additionally, zinc toxicity from excessive zinc intake (150-450 mg per day) can cause chronic effects such as low copper status, altered iron function, and reduced immune function. 
Furthermore, zinc nasal sprays are considered controversial. According to some experts, zinc nasal sprays reduce cold symptoms, but other studies suggest it has no positive effect and may worsen existing conditions. 
Magnesium Aspartate Side Effects
Common side effects resulting from excessive magnesium intake (more than 350 mg per day) include nausea and abdominal cramping.  Rare side effects from magnesium toxicity include:
- Dizziness or fainting
- Muscle paralysis
- Troubled breathing 
Those with diminished kidney function are at a higher risk for magnesium toxicity, as kidneys filter excess magnesium. Magnesium toxicity also contributes to hypotension, lethargy, confusion, and disturbances in normal cardiac rhythm. 
Vitamin B6 Side Effects
Reported effects from excessive vitamin B6 ingestion include:
- Arrythmia (abnormal heart rhythm)
- Skin reactions
- Gastrointestinal effects (nausea, vomiting, abdominal pain)
- Persistent bleeding
- Decreased serum folic acid levels 
Additional vitamin B6 side effects include lower blood pressure, increased bleeding risk, and lowered blood sugar levels. 
Some people are particularly sensitive to vitamin B6, and experience adverse effects even at low dosages.  However, this allergic reaction is uncommon.
Anecdotal Side Effects
Now that we know each of ZMA’s components risks, it’s time to look at ZMA as a whole.
According to Barbie Brosohart, R.D. and nutritional counselor, ZMA supplements are generally considered safe, and most successful ZMA products have 11 mg vitamin B6, 450 mg magnesium, and 30 mg zinc.  So, they typically fall under the safe and tolerable recommended amounts.
While ZMA has not been fully tested for safety, anecdotal evidence suggests ZMA poses minimal side effect risks.
Some users experience vivid dreams, fevers, and headaches when taking ZMA products, however, and these examples are provided here:
“I am deployed to Africa and I we take a weekly Malaria pill called Mefloquine. It can give you vivid dreams if taken near when you go to to sleep, but when combined with ZMA max every night I had multiple very real feeling dreams. It did make me sleepy, but the dreams are vivid and they interfere with nice relaxing sleep.” –kyle (Amazon Verified Purchase)
“I did not have a good result with this product. I added it into my regimen at a half-dose and immediately began experiencing fever headaches and fatigue that would last for days. I stopped taking it, and the headaches went away after a day or two. I waited a little bit, then began taking it again. Same deal. Fever headaches, poor sleep, and fatigue. I tried to be fair to the product, so I cycled it again with the same result. Flushed the rest of the bottle. I had read some info on BB forums before taking that listed headaches, nausea, and fatigue as side effects of a zinc overdose. I don’t know if that was the case here (though I do take a mutli containing zinc). Either way, be sure to research before taking.”-BYEDYOO (Bodybuilding.com)
While these effects are uncommon and could be related to the particular products users were taking, it’s important to exercise caution before consuming any ZMA supplement.
-  “Zinc” Mayo Clinic.
-  Dietary Supplement Fact Sheet: Zinc Office of Dietary Supplements Reviewed June 05, 2013.
-  University of Maryland Medical Center “Zinc” Last reviewed June 30, 2011.
-  Dietary Supplement Fact Sheet: Magnesium Office of Dietary Supplements Reviewed July 13, 2009.
-  “Magnesium” Mayo Clinic.
-  Higdon, Jane Ph.D., Linus Pauling Institute Micronutrient Research for Optimum Health “Magnesium” written April 2003.
-  Dietary Supplement Fact Sheet: Vitamin B6. Office of Dietary Supplements Reviewed June 05, 2013.
-  “Vitamin B6 (pyridoxine)” Mayo Clinic.
-  Freedman, Lisa. “Supplement Guide: ZMA.” Men’s Fitness.