Creatine has one of the strongest safety records of any supplement, and for most healthy adults side effects are minor. The most consistent one is a small increase in body weight, usually a pound or two early on, from extra water pulled into the muscles. That is water, not fat, and for many people it is part of how creatine supports muscle.
The other real one is mild stomach upset, such as bloating or loose stools. This is almost always linked to taking a large amount at once, especially on an empty stomach during a loading phase. Splitting the dose, or simply taking 5 g a day with food and skipping loading, usually avoids it.
Several famous side effects do not hold up. Good research has not found that creatine causes muscle cramps, dehydration, or kidney damage in healthy people, despite the gym reputation. It is also not a stimulant, so it will not keep you awake.
People who should be more careful, and talk to a doctor first, include those with kidney disease, anyone pregnant or breastfeeding, and teenagers, where there is less research.
Sources
- Dietary Supplements for Exercise and Athletic Performance, NIH Office of Dietary Supplements
- ISSN position stand: safety and efficacy of creatine supplementation, Journal of the International Society of Sports Nutrition, PMC
- Common questions and misconceptions about creatine supplementation, Journal of the International Society of Sports Nutrition, PMC
This page is general information, not medical advice. Creatine is a dietary supplement, not a medicine. It is well studied and considered safe for most healthy adults, but talk to a doctor before starting if you have a health condition such as kidney disease, are pregnant or breastfeeding, or take prescription medication.