Creatine safety: side effects, interactions and who should skip it

What the safety research covers, and what it does not

Creatine is among the most studied supplements, and the overall verdict is reassuring. The International Society of Sports Nutrition's 2017 position stand concluded that it is safe and well tolerated across the doses and durations in the literature it reviewed.

A 2025 analysis of 685 trials found no overall increase in side effects compared with placebo. A small difference in reported muscle cramping appeared when each study was counted equally, then disappeared once studies were weighted by how many people were in them.

The caveat is who was studied. Most of this research enrolled healthy adults, mostly taking creatine monohydrate. Pregnant people, children, and people with specific medical conditions are thinly represented, so 'well tolerated' describes the compound in tested groups, not a guarantee for every reader. For the broader picture, see our creatine topic page.

Side effects that have actually been documented

The list is shorter and more specific than most online summaries suggest. Four findings come up repeatedly.

• Water retention. In a one-week trial, creatine raised total body water by about 2% and lifted fat-free mass readings on three different measurement methods. That is a water effect, not fat gain, and the timeframe was too short to reflect new muscle. A heavier scale or snugger waistband in the first week or two most likely reflects this.
• Diarrhea tied to serving size. In a 28-day trial of soccer players, a single 10 g dose caused diarrhea about twice as often as the same 10 g split into two 5 g servings (55.6% versus 28.6%). Placebo was 35.0%, so stomach complaints were common regardless. Splitting larger amounts is the practical lesson.
• Stomach upset with caffeine. In a 5-day loading trial, nobody taking creatine alone reported GI side effects. Mild discomfort appeared in 4 of 13 people taking creatine with a caffeine supplement. It is a small trial, but a pattern worth noticing if you stack the two.
• A hormone marker, not hair loss. One small trial in 20 male rugby players found blood DHT rose after creatine loading. DHT is linked to hair loss in people who are genetically susceptible. That trial never measured hair or scalp outcomes, and no larger trial has followed up.

Muscle cramps and heat illness deserve a separate note. An older caution against creatine in hot conditions has not held up well. A 2008 review found later trials did not support it, and a randomized crossover trial found a week of high-dose creatine did not worsen hydration, temperature regulation or heat-illness symptoms during exercise in the heat. Observational data from college football teams found cramping was not higher among creatine users. Observational data cannot prove cause, but nothing here points toward harm.

Kidneys and liver: what a blood test can and cannot tell you

Creatine breaks down into creatinine, the waste product that standard kidney blood tests measure. Taking creatine can therefore raise your creatinine number without the kidneys working any worse. That makes the result easy to misread, which is why it helps to tell whoever orders your labs that you take it.

A review of 19 studies, covering 5 to 30 g a day for periods from 5 days to 5 years, found no known harmful effect on kidney function in healthy people without existing kidney disease. The same review advised against use in people who do have kidney disease. An 8-week trial in football players also found no significant change in liver or kidney blood markers.

The liver is murkier. Human research on creatine in people with chronic liver disease is essentially absent. Animal work points in opposite directions: in mice, creatine was linked to less liver fat and damage on a high-fat diet but more on alcohol. A review of liver metabolism also raised a more speculative concern, drawn from a small number of studies, about oxidative stress. None of this is established in people, but it is a reason for anyone with liver disease or heavy alcohol use to ask a clinician rather than guess.

Interactions with drugs and other supplements

Here the honest answer is mostly 'untested.' We found no trial pairing creatine with a specific prescription drug class, so there is no documented interaction to cite and no proof of safety either. The kidney caution is the one concrete lead: if you take a medication that affects the kidneys, including some long-term pain relievers and blood pressure drugs, ask your pharmacist before adding creatine. Our interactions guide covers the same ground in more detail.

For common supplement partners, the evidence is more specific, though still thin.

Multi-ingredient pre-workouts are a gap. The caffeine trial tested caffeine and coffee only, so it cannot speak to a blend with a dozen ingredients.

Who should avoid creatine or ask first

No group below has been proven to be harmed by creatine in the studies we reviewed. The advice reflects missing data, one explicit review recommendation for kidney disease, and a few signals worth taking seriously. Our label guidance on who should not take creatine follows similar lines.

Women are not a separate caution. A 2026 meta-analysis of 7 trials in postmenopausal women found no more side effects than placebo, though data on perimenopausal women are limited.

Warning signs to stop, and how to lower the odds of trouble

No trial has defined formal stopping rules, so the list below is practical judgment rather than a validated protocol. Stop and contact a clinician if you notice any of these.

• Diarrhea or stomach pain that persists after you cut each serving to 5 g or less
• Noticeable swelling, a marked drop in urination, or new fatigue and nausea, particularly if you have any kidney risk
• Palpitations, an irregular heartbeat or chest discomfort
• Unusually elevated mood, racing thoughts or much less need for sleep, especially with a mood disorder
• Any new symptom that began soon after starting and does not settle

To keep risk low, use plain creatine monohydrate. A 6-week trial found about 2.3 g a day with no loading phase raised blood creatine and improved fatigue resistance, so a low steady dose is a reasonable starting point. If you do load, divide it into servings of about 5 g. Tell your doctor you take creatine before any kidney blood test.