Creatine Side Effects: What the 2025 Safety Evidence Actually Shows

If you have spent any time in a gym, or anywhere near the comment section of a fitness video, you have probably heard someone say that creatine “messes up your kidneys” or “causes cramps and bloating.” Maybe you have even held off on one of the most thoroughly researched supplements in sports nutrition because a friend warned you away. Or a physician who last read about creatine in 1999.

Two landmark papers published in 2025 in the Journal of the International Society of Sports Nutrition make the most definitive case yet that those fears are unfounded. Led by Richard B. Kreider of Texas A&M University, the research team analyzed every human clinical trial on creatine monohydrate they could get their hands on. All 685 of them, enrolling more than 26,000 participants. They asked a straightforward question: do people taking creatine report more side effects than people taking a placebo?

Across 35 different categories of side effects, the answer was no.

Sit with that. Creatine is not merely “probably safe.” At a scale rarely seen for any dietary supplement, the evidence says its side effect profile is essentially indistinguishable from a sugar pill.

How the study was designed

Kreider’s team took an exhaustive approach that previous safety reviews simply could not match. The volume of creatine research has exploded over the past decade. The 685 trials covered an average dose of 12.5 grams per day for nearly 65 days. Some studies ran as long as 14 years and used doses up to 30 grams daily. This was not a narrow, curated slice of the literature. It was the literature.

They pooled all reported adverse events from both the creatine and placebo arms of every trial and calculated prevalence rates: what percentage of people in each group reported any given side effect. They compared those rates statistically. Then, for good measure, they scoured the World Health Organization’s global adverse event reporting database, which contains 28.4 million reports, to see how often creatine was flagged.

The companion paper, led by Adriana Gil and published alongside the main analysis, took a different statistical lens. Instead of treating all trials as one pooled dataset, Gil’s team analyzed the frequency and prevalence of side effects per trial. The two papers reinforce each other. Slice the data by prevalence or by per-trial frequency. The result holds.

What the numbers actually say

The headline statistic from the Kreider analysis is almost anticlimactic in its clarity. Across all 685 trials, 4.60 percent of participants taking creatine reported any side effect. Among those taking a placebo: 4.21 percent. The difference was not statistically significant (p=0.828). Give creatine to 100 people and a placebo to 100 people, and roughly four people in each group would mention something. You could not tell which group was which from that information alone.

Gil’s frequency analysis found the same pattern for individual side effects. Gastrointestinal complaints. Muscle cramping. Dehydration. Renal markers. Not one of 35 evaluated side effects appeared more often in the creatine group than in the placebo group at a rate that cleared statistical significance. In several categories, the placebo group actually had a slightly higher rate of reports. That kind of finding underlines how much of the “creatine side effect” narrative may be driven by expectation rather than pharmacology.

Then there is the WHO adverse event data. Of 28.4 million reports worldwide, only 204 mentioned creatine. That is 0.00072 percent. Even among those, nearly half incorrectly listed creatine as the suspect product when the actual supplement did not contain it. The global pharmacovigilance system catches real medication risks with sensitivity. It barely registers creatine as a blip.

What about the kidneys?

The kidney question deserves its own section. It is the most persistent worry, and it stems from a genuine biochemical fact: creatine supplementation raises serum creatinine, the standard blood marker used to estimate kidney function. Creatinine is a breakdown product of creatine. Take more creatine, produce more creatinine. On a basic metabolic panel, that can look like your kidneys are struggling.

A 2025 systematic review and meta-analysis published in BMC Nephrology addressed this directly. The analysis found a small but statistically significant increase in serum creatinine with creatine supplementation (mean difference of 0.07 µmol/L, 95% CI: 0.01 to 0.12, p=0.03). Critically, there was no corresponding drop in glomerular filtration rate, the actual measure of how well the kidneys are filtering blood. Serum creatinine went up because the body was making more of it, not because the kidneys were failing to clear it.

Kreider’s own analysis of renal adverse events across the 685 trials reached the same conclusion: no difference between creatine and placebo groups. Igor Longobardi and colleagues, writing in Frontiers in Nutrition in 2025, put it plainly: “Current evidence does not support a link between its supplementation and increased cancer risk nor renal dysfunction in humans.”

None of this means that someone with pre-existing kidney disease should take creatine without medical supervision. The trials that underpin the safety evidence largely enrolled healthy adults. If your kidneys are already compromised, the equation changes, not because creatine becomes toxic, but because the safety data in that population is thin. That is a gap worth acknowledging. Not a reason to panic.

GI discomfort, cramping, and water weight

Other common concerns are more nuanced. Stomach upset. Muscle cramps. Water retention. The Kreider analysis found no statistically significant increase in gastrointestinal side effects or cramping at the aggregate level. But a few individual studies did report higher rates in the creatine arm. This is consistent with what anyone who has taken creatine at high doses already knows: taking 20 grams at once on an empty stomach is a reliable way to spend an uncomfortable afternoon.

The loading-phase protocol was standard in early creatine research and is still common in gym culture: 20 to 25 grams per day, split into four or five doses for the first week. The 2025 safety data suggest that most of the GI complaints in the literature come from these high-dose, short-duration loading protocols. A maintenance dose of 3 to 5 grams per day, taken with food, appears to avoid the issue almost entirely.

Water retention is real but mechanistically distinct from bloating in the uncomfortable sense. Creatine pulls water into muscle cells. That is part of how it works. Increased intracellular hydration is one of the mechanisms proposed to explain its performance benefits. This typically adds one to two kilograms of body mass within the first few weeks, almost entirely intramuscular water. It is not edema. It does not raise blood pressure. For strength athletes, it is generally considered a feature, not a bug.

Why the perception gap persists

If 685 trials and 26,000 participants cannot shift public perception, what can?

Part of the answer is structural. Creatine was swept up in the same post-1990s regulatory panic that tarred ephedra and androstenedione. It got lumped together with “performance-enhancing substances” in a way that implied danger without evidence. The FDA has never issued a creatine-specific safety warning. The cultural association stuck anyway.

Another part is commercial. The supplement industry has a financial incentive to sell “next-generation” creatine alternatives. Buffered creatine. Creatine hydrochloride. Creatine nitrate. Each one implies that monohydrate causes side effects the newer forms avoid. The irony is that creatine monohydrate is the form on which virtually all of the safety evidence is based. If you are worried about side effects, the evidence points toward monohydrate, not away from it.

Social media amplifies both dynamics. A single anecdotal post about “creatine destroying my kidneys” can reach millions of people. A 685-trial meta-analysis never will. The algorithm does not care about sample sizes.

Who should think twice

The safety picture is overwhelmingly reassuring. It is not a blanket assertion that creatine is risk-free for every human on Earth. The evidence base has gaps worth noting.

People with diagnosed kidney disease were largely excluded from the trials. The BMC Nephrology meta-analysis authors specifically flagged this as an area where caution is warranted, not because creatine is known to cause harm in this population, but because it has not been adequately studied. If you have chronic kidney disease, the decision to supplement should involve a nephrologist who understands the difference between elevated serum creatinine from supplementation and elevated serum creatinine from impaired clearance.

Pregnant and breastfeeding people are another evidence gap. Creatine is present in breast milk and plays a role in fetal neurodevelopment, but the safety trials have not enrolled pregnant participants. The theoretical case for creatine in pregnancy is actually interesting. Some researchers have proposed it as a neuroprotective agent. The evidence is not there yet.

People taking nephrotoxic medications should also be cautious, for the same reason as those with kidney disease: the relevant studies have not been done.

For everyone else, healthy adults, adolescents engaged in sport, older adults using creatine for sarcopenia prevention, the 2025 evidence is as close to a clean bill of health as nutritional epidemiology gets.

Where the evidence lands

Two comprehensive 2025 analyses of 685 human trials, reinforced by a separate kidney-specific meta-analysis and a review of 28.4 million adverse event reports, converge on the same conclusion. Creatine monohydrate supplementation, at doses up to 30 grams per day for periods of up to 14 years, does not increase the risk of side effects compared to placebo.

That gap between evidence and perception is significant. It is worth asking why a supplement this well-studied still carries a reputation it does not deserve. Part of the answer is that “nothing to see here” is a harder message to sell than a scare story. Null results do not go viral.

If you are a healthy adult considering creatine, the evidence suggests you can take it with confidence. Start at 3 to 5 grams per day, with food. Skip the loading phase if you want to avoid the only side effect the literature can reliably attribute to it: a mildly unsettled stomach at high acute doses. As always, consult your doctor before starting any supplement.

References

1. Kreider RB, Gil A, et al. Safety of creatine supplementation: analysis of the prevalence of reported side effects in clinical trials and adverse event reports. J Int Soc Sports Nutr. 2025. https://doi.org/10.1080/15502783.2025.2488937
2. Gil A, Kreider RB, et al. Safety of creatine supplementation: analysis of the frequency of reported side effects in clinical trials. J Int Soc Sports Nutr. 2025. https://doi.org/10.1080/15502783.2025.2533688
3. Effect of creatine supplementation on kidney function: a systematic review and meta-analysis. BMC Nephrol. 2025. https://doi.org/10.1186/s12882-025-04558-6
4. Longobardi I, et al. A short review of the most common safety concerns regarding creatine ingestion. Front Nutr. 2025. https://doi.org/10.3389/fnut.2025.1682746
5. Creatine supplementation is safe, beneficial throughout the lifespan. Front Nutr. 2025. https://doi.org/10.3389/fnut.2025.1578564
6. Wolf M. Should you worry about the side effects of creatine? Stronger by Science. 2025.