People on creatine reported side effects about as often as on placebo
Across 685 clinical trials, side effects turned up in 13.7% of the creatine groups and 13.2% of the placebo groups, and kidney markers came out no different.
What the study found
Side effects ran 13.7% with creatine and 13.2% with placebo
Across 685 clinical trials, side effects turned up in 13.7% of the creatine groups against 13.2% of the placebo groups, and kidney-function markers came out no different. Creatine appeared in 0.00072% of 28.4 million adverse-event reports, usually alongside other products.
The caveat · Built to test performance, not harm
These trials were built to test performance rather than to hunt for harm, so anything rare or slow enough to slip past them would have slipped past. The adverse-event reports are filed voluntarily, which distorts the count in both directions. Average intake across the pooled trials was about 12.5g of creatine a day.