The guide

Creatine side effects: which are real, and your kidney test

By GyroscopeUpdated November 15, 202617 sources

For healthy adults taking 3 to 5 g a day, yes. The real side effects are water weight in the first weeks, a higher creatinine number on blood tests, and an upset stomach from big single doses. The kidney and hair fears don’t hold up in healthy people. Ask your doctor first if you have kidney disease or you’re pregnant or breastfeeding, and we don’t give a dose to anyone under 18.

Creatine has a reputation problem. It builds muscle, it comes in big tubs from the sports shelf, and it shows up on blood tests. People hear that it damages kidneys, makes your hair fall out, dehydrates you and causes cramps, and that it’s basically a steroid.

Some of that comes from real findings that got stretched, and some from guesses that later trials put to the test. In the early 2000s, the American College of Sports Medicine advised people cutting weight or training hard in the heat to avoid creatine, based mostly on theory. In one survey of 219 athletes, 38% of the 90 who used creatine said it had side effects, such as cramps. Controlled trials, where nobody knows who’s on creatine, give a much calmer picture.

Which side effects are real?

The only side effect that turns up consistently in the trials is weight gain. The International Society of Sports Nutrition says that after more than 1,000 studies since creatine became popular in the early 1990s. Studies of patients have used up to 30 g a day for as long as five years.

One 2025 count from a creatine research lab looked at 685 creatine trials. Some side effect was reported in 13.7% of the creatine groups and 13.2% of the placebo groups. Those numbers count trials that reported anything, rather than people, and they come from a conference summary. Stomach complaints showed up in 4.9% of creatine groups against 4.3% of placebo groups, and cramps or pain in 2.9% against 0.9%, so the small differences aren’t all in creatine’s favor.

Why does creatine raise creatinine?

Because creatinine is what creatine turns into. About 1 to 2% of the creatine in your muscles breaks down every day into creatinine, which your kidneys pass into urine. Fill your muscles with more creatine and you make more creatinine, so there’s more in your blood at the same kidney speed.

Your kidney score on a blood test, the eGFR, is usually worked out from your creatinine, your age and your sex. It assumes your creatinine comes from an ordinary amount of muscle. Feed it a higher creatinine and it prints a lower score, with no way to know the extra came from a scoop. Lots of muscle and a meaty diet raise creatinine too.

Picture a sink. The kidney score guesses how fast the drain works by how full the sink is. Creatine turns the tap up a little, so the sink sits a bit fuller and the score guesses the drain is slower, while the drain works exactly as before.

What the kidney trials found

A 2026 review pooled 26 trials and 1,036 people. Creatine raised creatinine by 0.14 mg/dL on average. The kidney score worked out from creatinine fell by about 11 mL/min. Kidney filtering measured directly, with a tracer test that doesn’t rely on creatinine, didn’t fall at all. A second 2026 review of 20 trials found creatinine 0.13 mg/dL higher, with no difference in urea or eGFR.

The direct trial of the better test came in 2008. Bruno Gualano’s group at the University of São Paulo gave 18 healthy men about 10 g of creatine a day or a placebo for 3 months while they trained. Cystatin C, a kidney marker that muscle barely moves, didn’t rise in the creatine group. It fell in both groups.

What is cystatin C, and when does it help?

It’s a small protein your body makes at a steady rate, cleared by the kidneys like creatinine. Unlike creatinine, it hardly depends on your muscle. In a 2008 study of 170 healthy adults, creatinine tracked lean mass and cystatin C didn’t, and active people had higher creatinine with the same cystatin C.

The National Kidney Foundation says a cystatin C test can help when creatinine may mislead, including in older adults and people with a lot of muscle. It also notes cystatin C may not be accurate in people with an untreated thyroid condition or those taking steroids. The creatinine check shows how far above your lab’s range creatine usually puts you, and never works out a kidney score.

Should you stop creatine before a blood test?

Tell whoever orders the test instead. Your muscle stores take about a month to fall after you stop, 30 days in the 1996 trial and 4 to 6 weeks by the International Society of Sports Nutrition’s count, and the creatinine comes from those stores. A few days off probably won’t clear it, though no study has timed it. Saying how much you take, and asking about cystatin C if your creatinine is high, gives your doctor what they need.

Does creatine cause hair loss?

There’s no good evidence it does. The worry comes from a 2009 study of 20 college rugby players in South Africa. After a week of loading, their DHT, a hormone linked to male pattern hair loss, was 56% higher, and it was still 40% higher two weeks later. Testosterone didn’t change, the DHT stayed within normal limits, and nobody looked at anyone’s hair.

In 2025, a trial finally did. Forty-five men who lifted took 5 g a day or a placebo for 12 weeks, and 38 finished. Their hair was measured for density, thickness and follicle counts, and their hormones were tested. There was no difference in DHT or in any hair measure. That trial only included men aged 18 to 40, so no trial has tested women or men already losing their hair. The hair loss myth has the full story.

Does creatine cause cramps or dehydration?

The trials found the opposite. In a season of college football, players on creatine had fewer cramps, less heat illness and dehydration, fewer muscle strains and fewer total injuries than players who didn’t take it.

Who should ask a doctor first?

If you have kidney disease. Some experts suggest people with kidney disease check with their doctor before taking creatine, out of caution. Your blood tests are how your doctor tracks your kidneys, and creatine changes one of the numbers.

If you’re pregnant or breastfeeding. Researchers are interested in creatine in pregnancy, but the evidence is mostly from animals and early human work. There isn’t enough to give a dose, so ask your doctor or midwife.

If you’re under 18. We don’t give a dose. The American Academy of Pediatrics strongly opposes performance-enhancing substances, supplements included, for children and teens. Its 2016 report says most young athletes don’t gain much from them beyond what puberty, good food and training already give. New York bans selling muscle-building supplements to anyone under 18, and creatine is one of the ingredients that can mark a product as muscle building under that law. In 2025, doctors reported a 17-year-old who developed kidney injury after a six-day high-dose loading regimen. One case can’t show cause, but it’s one more reason a teenager shouldn’t load. strength.guide has whether teenagers should lift.

Who says what, and when

• International Society of Sports Nutrition, 2017. Creatine monohydrate is safe for healthy people, including at up to 30 g a day for five years in patient groups. The paper says its preparation was funded by the Council for Responsible Nutrition, and several of its authors have industry ties.
• National Kidney Foundation, last updated July 2023. Cystatin C can help when creatinine may mislead, such as in people with a lot of muscle.
• American Academy of Pediatrics, 2005 and 2016. Strongly against performance-enhancing substances, supplements included, for children and teens.
• New York State, revised 2024. No sales of weight-loss or muscle-building supplements to anyone under 18.