← The science

Creatine side effects — is it safe?

The kidney question

This is the worry people raise most, and it comes from a misunderstanding. Creatine breaks down into creatinine, and creatinine is what a standard blood test uses to estimate kidney function. Take creatine and your creatinine reading can nudge up — not because anything is wrong with your kidneys, but because you are eating more of the thing the test measures. In people with healthy kidneys, long-term trials have not shown creatine causing damage. If you have existing kidney disease, that is a conversation to have with your doctor first.

Water and "bloating"

Creatine draws a little water into the muscle cell — typically half a kilo to two kilos in the first couple of weeks. It sits inside the muscle rather than under the skin, so it tends to read as firmer rather than puffy, and it levels off once you are saturated. This is the one effect that is genuinely, reliably creatine.

Cramps and dehydration

The old gym rumour was that creatine causes cramps or dehydration. Controlled research points the other way if anything — athletes taking creatine, including in the heat, have not shown higher cramp or dehydration rates. Drink normally and you are fine.

Stomach upset

A large single dose — the classic 20g loading day taken all at once — can unsettle some stomachs. Splitting it, or simply skipping loading and taking 3–5g a day, avoids it for almost everyone.

The bottom line

For healthy adults, the safety record is about as strong as a supplement gets. The sensible caveats are the ordinary ones: if you are pregnant, have kidney disease, or are on medication and unsure, check with your GP first.