Creatine Side Effects: What the Evidence Shows and Who Should Avoid It

Creatine has two reliable side effects: about a kilogram of water weight, and an upset stomach if you take too much at once. Everything else on the usual list of worries, kidney damage, liver damage, hair loss, cramps, dehydration, has been tested and not found in healthy adults at 3 to 5 g a day. The one real complication is that creatine raises creatinine in your blood, which is the marker doctors use to check your kidneys, so it can make a kidney-function test look worse than your kidneys are. That is the main reason doctors are cautious, and it is worth understanding properly.

• Common: 0.8 to 1 kg of water inside muscle; gut discomfort with single doses of 10 g or more
• Not shown in healthy adults: kidney or liver harm, hair loss, cramps, dehydration, dangerous interactions
• The catch: a raised creatinine reading on blood tests, which is a measurement effect, not damage
• Check with a GP first if: you have kidney disease, are pregnant or breastfeeding, are under 18, or take medicines that affect the kidneys
• Daily use: safe at 3 to 5 g for years in the studies that have looked

Why do doctors say no to creatine?

Usually for one of three reasons, and only one of them is about creatine itself. None is about what creatine does in muscle.

The creatinine problem. Your body breaks creatine down into creatinine, which the kidneys clear. Doctors estimate how well your kidneys filter, the eGFR, from the creatinine level in your blood: the more creatinine, the lower the estimated filtration. The NHS describes this test and the threshold of about 90 ml/min for healthy kidneys.¹ Creatine supplementation raises blood creatinine without changing how well the kidneys actually work, so the estimate drifts downwards. A 2025 meta-analysis of 12 trials found a small rise in serum creatinine and no change in measured filtration rate.² A GP who sees a borderline eGFR in a fit 30-year-old and does not know they take creatine will quite reasonably worry. Tell your doctor you take it before any blood test, and the confusion disappears.

Caution about the unknown. Many doctors trained when the long-term data did not exist, and no is the safe default when you are not sure. The data now exists: the International Society of Sports Nutrition's position stand and a 2025 review of the whole literature find no safety signal at recommended doses.^{3, 4}

A genuine reason in your case. If you have reduced kidney function, a condition under treatment, or you are pregnant, a doctor's no is specific advice, not a general view about creatine. Follow it.

Which organ is affected by creatine?

Muscle, in the sense that muscle is where creatine is stored and does its work. In the sense the question usually means, which organ does it harm, the answer from the evidence is none, in healthy adults.

Kidneys. This is the organ people worry about, because of the creatinine effect above. Across trials from one week to five years, kidney filtration has not changed with creatine in people with healthy kidneys.^{2, 3, 5} In people who already have kidney disease the evidence is much thinner, which is why they are told to seek advice first rather than told it is dangerous.

Liver. Liver enzymes have been measured in many creatine trials and have not shown a consistent change.^{3, 5} There is no evidence that creatine is bad for the liver.

Heart and blood pressure. No consistent effect on blood pressure has been found in trials in healthy adults. The water creatine holds is inside muscle cells, not in the bloodstream, so it does not behave like salt.⁶

Evidence: strong for kidney and liver safety in healthy adults at 3 to 5 g a day. Limited for people with existing kidney disease.

What are the actual side effects of creatine?

Is creatine safe to take every day?

Yes, at 3 to 5 g. Daily use is the point: it fills a store that drains if you stop. The longest controlled data runs to about five years in athletes taking up to 30 g a day in the early studies, with no adverse effect on health markers, and the position stand concludes that daily use at recommended doses is safe in healthy people.^{3, 4} There is no evidence that you need to cycle it, and no mechanism by which continuous use would cause harm that intermittent use avoids. How much to take each day is here.

What should you never mix creatine with?

The honest list is short, and most of it is about caution rather than a known reaction.

• Medicines that affect the kidneys. Long-term non-steroidal anti-inflammatory painkillers such as ibuprofen, diuretics ("water tablets") including spironolactone, and some blood-pressure medicines. No trial has shown a harmful interaction, but these drugs load the kidneys and creatine adds a variable to the picture. Ask your GP or pharmacist first.
• Alcohol. There is no direct interaction. Heavy drinking dehydrates you and undermines training and recovery, which blunts what creatine does. Moderate drinking does not stop creatine working.
• Caffeine. A persistent claim says caffeine cancels creatine. A 2022 systematic review found the evidence inconsistent: taking caffeine before a workout does not undo a creatine load, though very high daily caffeine throughout a loading week might blunt it, and both together can upset the stomach.¹⁰ Your morning coffee is not a problem.
• Antidepressants. Creatine has been given alongside the SSRI escitalopram in a controlled trial of 52 women at 5 g a day for eight weeks, with no difference in adverse events from placebo.¹¹ That is reassuring rather than a licence; if you take citalopram or another antidepressant, mention creatine to your prescriber.
• Cholesterol medication. No interaction is known. Statins can themselves cause muscle symptoms and raise creatine kinase, a different molecule, which sometimes causes confusion. Tell your GP you take creatine so test results are read correctly.

Who should not take creatine, or should check first?

• Anyone with kidney disease or reduced kidney function. The evidence of safety is in people with healthy kidneys. Speak to your specialist.
• Anyone pregnant, trying to conceive or breastfeeding. Creatine is being studied in pregnancy and nothing alarming has emerged, but the trials needed to recommend it do not exist yet. More here.
• Anyone under 18. Not because of a known harm: the reviews of adolescent use report no adverse events, and a 2026 systematic review found no short-term signal in kidney, liver or metabolic markers.^{12, 13} But the studies are few and short, and supplement labels in the UK say adults. A GP or sports dietitian can advise for a serious young athlete.
• Anyone with a condition under treatment or on regular medication. See the list above. The answer is usually yes, but it should be your doctor's yes.
• Anyone with bipolar disorder. Case reports have described mood changes with creatine in people with bipolar disorder. The evidence is weak, but it is a reason to ask first.

Common worries, answered briefly

Is creatine 100% safe?

Nothing is. Creatine is among the most studied supplements, with hundreds of trials and no serious adverse effect established in healthy adults at recommended doses.^{3, 4} That is as close to the answer as evidence gets.

Can creatine cause gout or raise uric acid?

There is no evidence that it does. Creatinine and uric acid are different molecules, and creatine trials have not reported gout. If you have gout, your consultant should know what you take, but creatine is not on the list of known triggers.

Does creatine affect sleep?

It is not a stimulant and does not disrupt sleep. Whether it helps people cope with sleep deprivation is a separate, early line of research.

Does creatine affect sperm or fertility?

No evidence of harm. Creatine occurs naturally in semen, and trials have not reported fertility effects, though none has studied it directly.

What we don't know

• Safety in people with existing kidney disease. Small studies suggest no harm at low doses, but nobody should rely on them without medical advice.
• Pregnancy. Under active study. No data yet to recommend for or against.
• Very long-term use at doses above 5 g. Most multi-year safety data is at 3 to 5 g.
• Drug interactions. Mostly untested rather than tested and clear. The cautions above are precautions.

Sources

1. NHS. Chronic kidney disease: diagnosis. https://www.nhs.uk/conditions/kidney-disease/diagnosis/
2. Effect of creatine supplementation on kidney function: a systematic review and meta-analysis. BMC Nephrology, 2025. PubMed 41199218.
3. Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 2017. PubMed 28615996.
4. Kreider RB, et al. Creatine supplementation is safe, beneficial throughout the lifespan, and should not be restricted. Frontiers in Nutrition, 2025. PubMed 40331098.
5. Antonio J, et al. Common questions and misconceptions about creatine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition, 2021. PubMed 33557850.
6. Powers ME, et al. Creatine supplementation increases total body water without altering fluid distribution. Journal of Athletic Training, 2003. PubMed 12937471.
7. Ostojic SM, Ahmetovic Z. Gastrointestinal distress after creatine supplementation in athletes: are side effects dose dependent? Research in Sports Medicine, 2008. PubMed 18373286.
8. Jagim AR, Stecker RA, Harty PS, Erickson JL, Kerksick CM. Safety of creatine supplementation in active adolescents and youth: a brief review. Frontiers in Nutrition, 2018. PubMed 30547033.
9. Does creatine cause hair loss? A 12-week randomized controlled trial. Journal of the International Society of Sports Nutrition, 2025. PubMed 40265319.
10. Elosegui S, López-Seoane J, Martínez-Ferrán M, Pareja-Galeano H. Interaction between caffeine and creatine when used as concurrent ergogenic supplements: a systematic review. International Journal of Sport Nutrition and Exercise Metabolism, 2022. PubMed 35016154.
11. Lyoo IK, et al. A randomized, double-blind placebo-controlled trial of oral creatine monohydrate augmentation for enhanced response to a selective serotonin reuptake inhibitor in women with major depressive disorder. American Journal of Psychiatry, 2012. PubMed 22864465.
12. Jagim AR, Kerksick CM. Creatine supplementation in children and adolescents. Nutrients, 2021. PubMed 33670822.
13. Rubinchuk A, Dulkoski Z, Persaud NA, Wallen M. Evaluating the safety of creatine monohydrate in adolescents: a systematic review of renal, hepatic, and cardiometabolic outcomes. Cureus, 2026. PubMed 42124755.

This article is general information, not medical advice. If you have a medical condition or take regular medication, check with your GP or pharmacist before starting creatine.