Creatine Side Effects and Warnings

Safety Issues

Creatine appears to be relatively safe. ¹ No significant side effects have been found with the regimen of several days of a high dosage (15 g to 30 g daily) followed by 6 weeks of a lower dosage (2 g to 3 g daily). A study of 100 football players found no adverse consequences during 10 months to 5 years of creatine supplementation. ² Contrary to early reports, creatine does notappear to adversely affect the body's ability to exercise under hot conditions and might even be beneficial. ³ Dividing the dose may help avoid gastrointestinal side effects (diarrhea, stomach upset, and belching). In one study of 59 male soccer players, two separate 5 g doses was associated with less diarrhea than a single 10 g dose. ⁴ However, there are some potential concerns with creatine. Because it is metabolized by the kidneys, fears have been expressed that creatine supplements could cause kidney injury, and there are two worrisome case reports. ⁵ However, evidence suggests that creatine is safe for people whose kidneys are healthy to begin with, and who don't take excessive doses. ⁶ Furthermore, a 1-year, double-blind study of 175 people with amyotrophic lateral sclerosis found that use of 10 g of creatine daily did not adversely affect kidney function. ⁷ Nonetheless, prudence suggests that individuals with kidney disease, especially those on dialysis, should avoid creatine supplements.

Another concern revolves around the fact that creatine is metabolized in the body to the toxic substance formaldehyde. ⁸ However, it is not clear whether the amount of formaldehyde produced in this way will cause any harm. Three deaths have been reported in individuals taking creatine, but other causes were most likely responsible. ⁹ It has also been suggested that use of oral creatine would increase urine levels of the carcinogen N-nitrososarcosine, but this does not seem to be the case. ¹⁰ A few reports suggest that creatine could, at times, cause heart arrhythmias . ¹¹ As with all supplements taken in very high doses, it is important to purchase a high-quality form of creatine, as contaminants present even in very low concentrations could conceivably build up and cause problems.