What are the side effects of creatine? Mostly mild, and not kidney damage

The side effects of creatine that hold up in controlled trials are stomach upset and water weight. A 2026 review of three decades of creatine research reports that pooled analyses from hundreds of clinical trials find no greater rate of adverse events on creatine than on placebo [1], at the amounts normally studied, which are 3 to 5 grams a day of creatine monohydrate, the form these trials almost always used, or about 0.1 grams per kilogram of body weight [6][9].

Kidneys carry nearly all of the worry. A systematic review screened 290 studies, read 15 in detail and pooled the results of 6, concluding there was no kidney damage at the doses and durations those studies used [2]. About 90% of swallowed creatine is cleared by the kidneys and passed out in urine, which is why the question keeps getting asked, and healthy kidneys do that without a measurable change in how well they filter [11].

The longest safety trial gave 4 grams a day to 40 people with Parkinson's disease for two years, against 20 on placebo [4]. Creatinine in the blood went up, as expected. Cystatin C, a second kidney marker that creatine does not disturb, stayed normal, as did every other kidney measure [4]. Stomach complaints were the main side effect reported.

The complication is a measurement one. Creatine raises creatinine, the waste product your body makes when it burns creatine, and creatinine is what laboratories measure to estimate how well your kidneys filter [3]. A raised reading can look like chronic kidney failure in someone whose kidneys work normally [3]. On a high-protein diet the picture blurs further, because protein lifts a second waste marker, urea, at the same time [3].

Water weight is the one physical effect that turns up reliably, and how much of it you get depends on the dose. Twenty-seven adults aged 18 to 22 took about 20 grams a day for a week and gained 1.1 kg of fat-free mass on a DEXA scan, a type of body scan that separates fat from everything else, with total body water up 2% [7]. At roughly 2.3 grams a day for six weeks, 20 healthy young adults showed no change in body mass, fat-free mass or total body water at all [8].

Women are thinly studied. Of 656 creatine studies, 58 were in women only, and 29 of those tracked side effects across 951 participants [5]. There were no deaths and no serious adverse events, and rates of total side effects, stomach complaints, weight gain and kidney and liver measures came out no different from placebo [5].

Cramping and dehydration have the weakest support of anything on the list. An American College of Sports Medicine panel concluded there is no definitive evidence that creatine causes stomach, kidney or muscle-cramping problems [9], and trials following athletes for five days, nine weeks and in some cases five years found no kidney harm and normal liver enzymes [10].

The alarming case reports do exist, and they share a pattern: people taking creatine alongside other supplements, or taking more than the studied amounts for months on end [12].

Creatine is a compound your muscles use to recycle energy for short, hard efforts. Your body disposes of it by converting it into creatinine, a waste product the kidneys filter into urine [3].

Take in more creatine and you make more creatinine, so the amount in your blood rises for reasons that have nothing to do with kidney health [3]. About 90% of what you swallow leaves by this route [11].

Laboratories do not measure filtering directly. They estimate it from the creatinine in a blood sample, so anything that raises creatinine can produce a result that reads as reduced kidney function [3].

The two-year trial separated the two effects. It measured cystatin C, a kidney marker cleared independently of creatine, and found it normal while creatinine was raised [4].

The water weight has a different cause. Creatine is stored in muscle and draws water in with it, which registers on a scale or a body-composition device as a gain in fat-free mass rather than as new muscle tissue [7].

One mechanical concern is left over. Creatine carries an amino group, the nitrogen-containing part of an amino acid, and clearing large amounts of any such substance gives the kidneys more work to do [10].

• The longest trial ran two years, and it was in people with Parkinson's disease rather than healthy adults [4]. Nobody has tested creatine over decades of continuous use [13].
• Creatine has not been studied in children or adolescents [13], and none of these papers looked at pregnancy or breastfeeding. Absence of data is not reassurance.
• Only about 9% of creatine studies have been run in women alone, 58 out of 656, and just 29 of those reported side effects at all [5].
• People with chronic kidney disease were kept out of these trials, which is why the reviews state plainly that creatine should not be used by them, or by anyone taking medicines already hard on the kidneys [3]. Whether that describes you is a question for a doctor who has your kidney results.
• Blood pressure and protein leakage into urine have barely been tracked in long-term creatine users, a gap one review named and could not close [11].
• Most participants were young exercising adults, often men and often athletes, so these numbers do not transfer automatically to older adults or to people managing other illnesses.
• The reassuring averages are averages. In the women's analysis the total side-effect count came out slightly higher on creatine than on placebo, by a margin too small and too uncertain to separate from chance [5], so no difference means none anyone could detect rather than none at all.
• Trials built specifically to hunt for harm are almost nonexistent, and much of what gets claimed about side effects rests on single case reports, which cannot establish cause [10].

The scenario that catches people out is a routine blood panel. Someone taking creatine has blood drawn, creatinine comes back above the reference range, the laboratory's estimate of kidney filtering looks low, and the result now points at early kidney disease [3].

The two-year trial shows what is going on underneath. Creatinine rose in the people taking creatine, while cystatin C and the other kidney markers stayed normal [4].

Saying that you take creatine before the blood is drawn, rather than after the number arrives, is what lets whoever reads it interpret the result properly and decide whether a second marker is worth checking [3].