Creatine side effects: what the research shows

By the DieticiansWorldwide.com editorial team · 17 October 2026 · Supplements & industry

The short answer: which side effects are real

Creatine attracts more safety rumours than almost any other supplement, partly because it is so widely used and partly because it changes a blood test that doctors use to check the kidneys. When you line the claims up against controlled trials, most fall away, a few hold up, and a small group of people genuinely need to be careful.

The International Society of Sports Nutrition (ISSN) states that "the only consistently reported side effect" of creatine supplementation has been weight gain, and that studies of up to 30 g a day for five years have found no harmful effects in otherwise healthy people (ISSN position stand, 2017). The ISSN is a sports nutrition society and several authors of its creatine papers have industry ties, so it is worth checking that independent reviews agree. On the main questions below, they broadly do.

Water retention and weight gain

Creatine pulls water into muscle along with it. According to the ISSN, early loading studies recorded a temporary rise in body fluid of around half a litre to a litre, roughly matching the extra weight seen that week.

What happens after the first week is less dramatic. A review of common creatine misconceptions by ISSN-affiliated researchers points out that several studies lasting 5 to 10 weeks found no significant increase in total body water. In one 8-week study, body water did rise more with creatine, but the ratio of muscle to water inside cells stayed the same as on placebo, suggesting the water tracked the new muscle (Antonio and colleagues, Journal of the International Society of Sports Nutrition, 2021).

So does creatine make you gain weight? Usually a little, and mostly early. If the number on the scale matters to you, skipping the loading phase and taking 3 g a day avoids the sharpest jump. If you are dieting, our guide to whether creatine helps with weight loss explains how to read the scale when creatine is in the picture.

Weight gain is a genuine issue in a few settings: weight-class sports before a weigh-in, endurance events where extra body mass slows you down, and people with heart or kidney conditions whose doctors monitor fluid closely.

Stomach upset, bloating and diarrhoea

Gut symptoms are the side effect people notice most, and they depend heavily on how much you take at once.

The clearest data come from a trial in 59 top-level male footballers randomised to 5 g twice a day, 10 g once a day, or placebo for 28 days (Ostojic and Ahmetovic, Research in Sports Medicine, 2008). Diarrhoea was reported by 55.6% of the single 10 g group, compared with 28.6% of the split-dose group and 35.0% of the placebo group. Splitting the same daily amount removed the excess.

The practical rules follow directly:

• keep any single serving to 5 g or less;
• if you load, spread the daily 20 g across four servings;
• dissolve powder fully in plenty of fluid, and take it with a meal if your stomach is sensitive;
• if symptoms continue, drop to 3 g a day, which reaches the same muscle stores more slowly.

Hair loss: where the worry came from

The idea that creatine causes baldness traces back to a single 2009 study of 20 college rugby players in South Africa. After a week of loading at 25 g a day, blood levels of dihydrotestosterone (DHT), a hormone involved in male-pattern hair loss, rose by 56%, and were still 40% above baseline after two further weeks at 5 g a day. Testosterone itself did not change (van der Merwe and colleagues, Clinical Journal of Sport Medicine, 2009). The study did not measure hair at all.

The ISSN misconceptions review lists the problems with relying on it: the finding has not been replicated, the creatine group started with DHT about 23% lower than the placebo group, values stayed within normal clinical limits, and ten of twelve other studies found no change in testosterone. It states that no study has reported hair loss or baldness in humans.

The direct test arrived in 2025. In a 12-week randomised trial of resistance-trained men aged 18 to 40 taking 5 g of creatine monohydrate or a placebo daily, there were no differences in DHT, in the DHT-to-testosterone ratio, or in hair count, density or follicle measures between groups, and kidney markers did not change either (Lak and colleagues, Journal of the International Society of Sports Nutrition, 2025). Only 38 men completed it, it lasted three months, and it did not record family history of baldness, so it cannot rule out an effect in men already prone to hair loss. But the claim now rests on much weaker ground than its popularity suggests.

Kidneys: creatinine is not the same as kidney damage

This is the side effect that worries clinicians most, and it is mostly a problem of interpretation.

Your muscles break creatine down into creatinine, which the kidneys clear. Labs use blood creatinine to estimate your glomerular filtration rate (eGFR), the standard measure of kidney function. Take extra creatine and creatinine can rise for reasons that have nothing to do with the kidneys, which can make an eGFR look worse than it really is.

Three meta-analyses have now tested whether anything more than that is going on:

• A 2019 review in the journal of the US National Kidney Foundation pooled six studies and concluded that creatine "does not induce renal damage in the studied amounts and durations" (de Souza e Silva and colleagues, Journal of Renal Nutrition, 2019).
• A 2025 review of 21 studies found a modest, transient rise in serum creatinine but no significant change in measured or estimated GFR, which the authors attribute to creatine turnover rather than kidney impairment (Naeini and colleagues, BMC Nephrology, 2025).
• A 2026 review of 20 randomised studies found serum creatinine about 0.13 mg/dL higher with creatine, but no difference in urea or eGFR, and called for trials lasting more than a year (Tsiaras and colleagues, Journal of Renal Nutrition, 2026).

The ISSN review adds that the original scare came largely from a 1998 case report of a young man who already had kidney disease.

What this means for you:

1. Healthy kidneys: recommended doses have not been shown to cause harm.
2. Known kidney disease, a single kidney or a transplant: do not take creatine unless your kidney team agrees. The trials mostly excluded you, and a rise in creatinine could hide a real decline.
3. Before a blood test: tell the person ordering it that you take creatine. Some clinicians may ask you to stop for a few weeks before retesting, or use a different marker of kidney function.

Dehydration, cramps and heat illness

Coaches once told athletes not to take creatine in hot weather because it might cause cramps or dehydration. A systematic review of ten controlled trials concluded that "no evidence supports the concept" that creatine hinders heat loss or upsets the body's fluid balance at recommended doses (Lopez and colleagues, Journal of Athletic Training, 2009).

The ISSN misconceptions review describes a study of 72 American college football players training in hot conditions in which creatine users had significantly less cramping and fewer heat illnesses than non-users. Surveys that reported more side effects in creatine users did not control for dose or for other supplements taken at the same time. Hydration still matters in the heat, but creatine is not a reason to drink less or more than your training requires.

Women, older adults and long-term use

Most safety data come from men, so a female-only analysis is useful. A 2020 systematic review found 29 studies in women that monitored adverse outcomes, with 951 participants, and reported no deaths or serious adverse events and no increase in total side effects, gut symptoms, weight gain, or kidney or liver problems compared with placebo (de Guingand and colleagues, Nutrients, 2020). Our guide to creatine for women looks at doses and benefits for women in detail.

Long-term data are thinner than short-term data but reassuring. A 2025 short review concluded that available research does not support a link between creatine and cancer, that studies consistently show no adverse kidney effects in healthy people, and that caution is still advised in people with existing kidney conditions and in pregnancy, where evidence is lacking (Longobardi and colleagues, Frontiers in Nutrition, 2025).

Who should check with a clinician first

Talk to your doctor, pharmacist or dietitian before starting creatine if any of these apply:

• Kidney disease of any stage, a kidney transplant, or a single kidney.
• Diabetes or high blood pressure with kidney involvement, or regular blood tests to monitor kidney function.
• Medicines that act on the kidneys or fluid balance, such as diuretics, some blood pressure tablets or regular anti-inflammatory painkillers. Few combinations have been studied, so check.
• Pregnancy or breastfeeding, because there are no human trials.
• Under 18. The ISSN considers creatine acceptable in young athletes only with supervision, a balanced diet, serious competitive training and recommended doses.
• Liver disease, heart failure or swelling, where fluid shifts and blood results need monitoring.
• Competitive athletes subject to anti-doping rules.

For athletes, the bigger risk is often not creatine itself but what else is in the tub. The International Olympic Committee's consensus statement on supplements warns that inadvertently swallowing substances prohibited under anti-doping codes "is a known risk of taking some supplements", and strongly advises expert professional help before an athlete starts using them (IOC consensus statement, British Journal of Sports Medicine, 2018). A batch-tested creatine monohydrate is the sensible choice if you compete. Our supplements hub explains what independent testing marks do and do not guarantee.

Creatine is not protein, and protein has its own limits

People often take creatine alongside a high-protein diet, and the two get confused. Creatine supplies no meaningful protein, and it does not change how much protein you need.

That matters because protein advice is in the middle of its own debate. The US recommended intake is 0.8 g per kg of body weight a day. A European geriatric expert group recommends at least 1.0 to 1.2 g per kg for people over 65 (PROT-AGE Study Group, 2013), and a 2025 joint advisory on GLP-1 treatment notes that targets of 1.2 to 1.6 g per kg have been proposed during active weight loss (Mozaffarian and colleagues, American Journal of Clinical Nutrition, 2025). For most healthy people, either range is safe. For people with chronic kidney disease, though, protein targets may be lower than the general advice, which is another reason to plan any supplement with your renal team. Our guide to how much protein you need explains the targets by age and goal.

If you are trying to raise your protein, start with food. Our high-protein snacks guide lists practical options, and our protein powder guide covers contaminants and label checks. For energy needs, try our calorie calculator.

Creatine and GLP-1 medicines

No randomised trial has yet tested creatine in people taking GLP-1 medicines such as semaglutide or tirzepatide, so its safety and benefit in that group are assumed rather than proven. The 2025 GLP-1 advisory lists gastrointestinal side effects as one of the main challenges of these medicines, so adding a supplement that can upset the stomach at high doses deserves care. Our guide to GLP-1 weight loss covers protein and muscle priorities first.

How to take creatine with the fewest side effects

1. Choose plain creatine monohydrate, the form behind nearly all the safety data.
2. Take 3 to 5 g a day. Loading is optional; skipping it means less early water gain and fewer stomach complaints.
3. Never take more than 5 g in one serving.
4. Take it with food and fluid if you have a sensitive stomach.
5. Tell your doctor before blood tests, and get advice first if you have kidney disease or take medicines that affect the kidneys.
6. If you compete, buy a batch-tested product.

Creatine is one of the better-understood supplements, but it is still a supplement. For our main guide to what it does and who benefits, see creatine monohydrate. If you have a health condition and want a plan that fits your medicines, you can book a session with a registered dietitian.

Try the free protein calculator