Quick answer

The one side effect seen consistently in creatine studies is weight gain, often 1 to 2 kg in the first month, mostly water held in muscle. Stomach upset is more likely with single servings of 10 g. Controlled trials have not found more cramps, dehydration or hair loss than with placebo.^1,2,3,4,5

Key facts

A 2026 analysis of 20 randomized trials found a small rise in blood creatinine, with no change in urea or estimated kidney filtration.⁶
Across 29 studies that tracked side effects in 951 women, creatine did not raise side effects or weight gain beyond placebo.⁷
The worry about hair traces back to one 2009 study of 20 rugby players, and its hormone result has not been repeated.^8,9
The ISSN reports no harm in studies using up to 30 g a day for as long as 5 years.²

Weight gain and water

Weight gain of about 1 to 2 kg in the first month, largely water held in muscle; it comes on faster with loading¹

Most of the early gain is water drawn into muscle along with the creatine. A loading week of about 20 g a day typically adds 1 to 3 kg within days. Training studies lasting 5 to 10 weeks found no lasting rise in total body water relative to muscle.⁹

If a quick jump on the scale matters to you, for example in a sport with weight classes, skip the loading week. A steady daily amount fills muscle more slowly, over three to four weeks, without the fastest early gain.^9,10

Stomach upset and serving size

Nausea, diarrhea or stomach upset have been reported by some users.¹

Diarrhea was more common with one 10 g serving a day (56 percent of players) than with two 5 g servings (29 percent) or placebo (35 percent) in a 28-day trial of 59 soccer players.³

The pattern points to splitting larger amounts. Studies with a loading week gave 20 g a day as four 5 g portions, and a review by ISSN researchers suggests keeping each serving to 10 g or less.^1,9

Kidneys and the creatinine blood test

Creatine breaks down to creatinine, a waste product the kidneys clear. Doctors use blood creatinine to estimate kidney function, so taking creatine can push that number up without any change in how the kidneys work.^1,6

A small rise in blood creatinine on lab tests, without a change in estimated kidney filtration⁶

The 2026 analysis found no change in urea or estimated filtration, but its authors still call for trials longer than a year. The ISSN position stand reports no kidney harm in healthy people at up to 30 g a day for up to 5 years, and mentions advice that people with kidney disease check with a doctor first.^2,6

If you have kidney disease or reduced kidney function, or take a medicine that affects the kidneys, ask your doctor before starting creatine. Mention it whenever you have blood work, so the result is read in context.

Hair loss and DHT

One 2009 study of 20 rugby players found that DHT, a hormone linked to hair loss in men, rose 56 percent after a week of loading and stayed 40 percent above baseline after two more weeks. Testosterone did not change, hair was not measured, and the finding has not been repeated.^8,9

A review by ISSN researchers points out that the DHT rise in that study stayed within normal limits, and that 12 other studies found either no change in testosterone or small rises of no clinical importance. No study has reported hair loss in people taking creatine.⁹

The first trial to measure hair directly came in 2025. Forty-five resistance-trained men took 5 g a day or a placebo for 12 weeks. In the 38 who finished, DHT, the ratio of DHT to testosterone, hair density and hair thickness did not differ between the groups. It was one trial, in men only, and several of its authors advise creatine makers.⁵

Cramps, dehydration and heat

Muscle cramps and heat intolerance have been reported anecdotally; the ISSN review found that controlled studies do not support them^1,2

Surveys of athletes once linked creatine to cramping, but they did not account for other supplements or for how much people took. In one, 91% of users took more than the usual 5 g a day. In a season-long study of 72 college football players in hot, humid weather, those who chose creatine did not report more cramping, dehydration or heat illness than those who did not.⁹

A review of 10 controlled trials found no evidence that creatine at recommended amounts hinders heat tolerance or fluid balance in athletes exercising in the heat.⁴

NIH notes reports that creatine may reduce range of motion and cause muscle stiffness, and says drinking enough fluid might lessen these uncommon effects.¹

Is creatine safe for teens?

NIH says that in most cases only adults should use performance supplements, and cites the American Academy of Pediatrics' view that they do not help teen athletes beyond good nutrition and training.¹¹

The ISSN takes a different view. Its position stand calls creatine acceptable for teens in supervised competitive training who eat well and stay within recommended amounts, and describes under-18 label warnings as a legal precaution. Its researchers' review found no adverse effects in teen studies, but noted that most of those studies did not check health markers such as kidney or liver tests.^2,9

We take the cautious side: anyone under 18 should talk with a doctor before taking creatine.

Who should ask a doctor first

You have kidney disease, or a doctor has told you your kidneys work less well than they should
You are pregnant or breastfeeding: no human trial has tested creatine supplements in pregnancy¹²
You take a medicine that acts on the kidneys
You are under 18

None of the official sources we checked, including NIH's fact sheets, DailyMed drug labels and MedlinePlus, lists a medicine that interacts with creatine. That is a gap in the evidence, not a guarantee, so bring your supplement list when you talk to your pharmacist.

Questions people ask

Does creatine cause bloating?

Some people feel puffy during a loading week, when weight can rise 1 to 3 kg, mostly as water inside muscle. Over weeks of training, studies found body water stayed in proportion to muscle. Taking 3 to 5 g a day without loading avoids the fastest gain.⁹

Is creatine a steroid?

No. Creatine has a completely different chemical structure from anabolic steroids, which are controlled drugs, and most studies find no change in testosterone. The body makes its own creatine from three amino acids.^1,9

Do I need to stop creatine before a blood test?

Ask the doctor who ordered the test. Creatine raises blood creatinine slightly without changing estimated kidney filtration, so a kidney result can look worse than it is. Telling the doctor you take it lets them read the number in context.⁶

Are the side effects different for men and women?

The same few effects are reported in both. A review of trials in women notes that quick weight gain during loading is more common in men, and pooled studies of women found no rise in side effects over placebo.^7,12

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.