Creatine side effects

The most consistently documented side effect of creatine is a small rise in total body water and fat-free mass measurements, not fat, showing up within the first week or two of use. Gastrointestinal upset, changes in a hormone linked to hair loss, and kidney function are each covered by specific, limited trials below — not a long, undifferentiated list of "possible side effects."

Water weight, not fat

A one-week trial gave 27 healthy young adults either creatine (0.3 g/kg body weight, roughly a loading dose) or a placebo, then measured body composition three different ways — DEXA, and two types of bioelectrical impedance. The creatine group's fat-free mass reading rose across all three methods (1.1-1.9 kg), and total body water rose about 2%. The authors attribute the fat-free-mass increase to water retention, not new muscle, given the one-week timeframe was too short for that. If a scale or a snugger waistband is the first thing someone notices on creatine, this is almost certainly what's showing up — not fat gain.

Gastrointestinal upset: mostly not from creatine alone

A 5-day loading trial (54 physically active men) tested creatine alone against creatine combined with caffeine or coffee, against placebo. No gastrointestinal side effects were reported at all in the group taking creatine by itself. Mild GI discomfort showed up only in the creatine-plus-caffeine group — 4 of 13 people. That's a small, specific finding, not evidence that creatine on its own commonly upsets the stomach; see creatine and medications: what to check for more on the caffeine combination specifically.

DHT and hair loss

A small crossover trial in 20 male rugby players found blood dihydrotestosterone (DHT) rose 56% after a week of creatine loading (25 g/day) and stayed 40% above baseline through two more weeks of maintenance dosing (5 g/day); testosterone itself didn't change. DHT is a hormone linked to hair loss in people already genetically susceptible to it — but this trial measured blood hormone levels only, never hair or scalp outcomes, and no larger trial has followed up on the finding since. It's a real, if thin and dated, data point on a hormone marker, not a demonstrated hair-loss effect.

Creatinine and kidney function

Creatine supplementation typically raises blood creatinine — the marker a standard kidney-function blood test measures — because creatinine is the waste product creatine itself breaks down into. A higher creatinine number from more creatine in the system isn't automatically the same thing as reduced kidney function, and a 19-study review found no known effect on kidney function, including glomerular filtration rate, at doses from 5 to 30 g a day for up to 5 years in people without pre-existing kidney disease. That review specifically advises against creatine use in people who have kidney disease, so if that's you, ask your doctor before taking any creatine supplement, regardless of dose.

What the broader safety literature says

The 2017 International Society of Sports Nutrition position stand concludes that short- and long-term creatine supplementation — including doses well above what our label directs, for as long as 5 years in the studies it reviewed — is safe and well tolerated in healthy people and a range of patient populations. That's a conclusion about the compound generally, based mostly on monohydrate trials, not a claim specific to any one brand's product.

Questions people ask

What are the side effects of creatine?

The most consistently documented one is a small increase in total body water and fat-free mass readings in the first week or two. Beyond that, the specific findings above — GI upset mainly in combination with caffeine, a DHT increase in one small trial, and creatinine changes that reflect normal creatine metabolism — are each narrower and more limited than a general "side effects" list suggests.

Does creatine make you bloated or puffy?

The water-retention effect described above (about 2% more total body water in one week) is the most likely explanation for a bloated or puffy feeling some people report, rather than a separate, undocumented effect.

Can creatine cause diarrhea?

The one trial above that isolated creatine from caffeine reported no gastrointestinal side effects in the creatine-only group. GI discomfort in that research showed up specifically in the group combining creatine with caffeine, not creatine by itself.

Does creatine affect your kidneys or liver?

For kidneys: a 19-study review found no known effect on kidney function at doses from 5 to 30 g/day for up to 5 years, in people without pre-existing kidney disease, though it advises against use in people who have kidney disease. We didn't find a comparable dedicated review specifically isolating liver function, so we're not making a claim on that here.

Can creatine cause hair loss?

The evidence tying creatine to hair loss is one small, dated trial showing a rise in blood DHT — a hormone linked to hair loss in genetically susceptible people — with no hair or scalp measurement in the same study, and no larger follow-up trial since. That's thinner than the claim usually implies.