In 2002, a meta-analysis in the Journal of Applied Physiology set out to find which supplements build muscle. The authors screened 250 of them. Only six had enough published trials to analyze at all. Creatine was one of only two that significantly increased both lean mass and strength during resistance training. Protein, chromium and androstenedione did not make the cut.
Twenty-four years later, that finding has held up. Most ingredients on the supplement shelf sit in a category this site keeps having to call preliminary or insufficient. Creatine does not. For one narrow outcome, repeated short bursts of hard effort paired with a training program, the evidence is good, replicated, and large enough to state in kilograms.
Saying that plainly matters, because honest reporting works in both directions. It also sharpens what follows. The kidney studies are routinely misread, sometimes by the person holding the lab printout. And the question parents keep asking, whether any state stops a 15-year-old from buying creatine, has an answer more complicated than either side claims.
What the performance research found
The most recent body-composition estimate comes from a 2024 meta-analysis in the Journal of Strength and Conditioning Research by Desai and colleagues at the University of New South Wales. The review was preregistered on the Open Science Framework before the authors looked at the data, which is unusual in this literature. Twelve studies in adults under 50 met the criteria.
Compared with resistance training alone, adding creatine increased lean body mass by 1.14 kilograms, with a 95 percent confidence interval of 0.69 to 1.59. Body fat percentage fell by 0.88 points and fat mass by 0.73 kilograms. Just over half the included studies were rated low risk of bias.
Strength numbers come from a separate 2024 meta-analysis in Nutrients by Wang and colleagues, covering 23 studies. Upper-body strength improved by a weighted mean difference of 4.43 kilograms and lower-body strength by 11.35 kilograms, both at p less than 0.001.
Read the participant list before the result. Twenty of those 23 studies enrolled only men. In the pooled data, men gained significantly on both measures and women showed no significant gains. That is not a finding that creatine fails in women. It is a finding that almost nobody has studied women properly, which is different and less satisfying.
The most conservative reading
A 2023 analysis in Nutrients led by Ryan Burke and Brad Schoenfeld at CUNY Lehman College took a stricter approach, including only trials that measured muscle directly with MRI, CT or ultrasound over at least six weeks. Across 10 studies and 44 outcomes, the pooled standardized estimate was 0.11, with a credible interval running from minus 0.02 to 0.25. The authors call that a very small effect: roughly 0.10 to 0.16 centimeters of added muscle thickness.
So the answer depends on the ruler. Body-composition scans show about a kilogram. Imaging a specific muscle shows something near the edge of detectability. Both numbers are real, and anyone quoting only the first is picking a favorite.
Older adults
A 2014 meta-analysis in Medicine and Science in Sports and Exercise by Michaela Devries and Stuart Phillips pooled 357 older adults across roughly 12.6 weeks of resistance training. Creatine plus training beat training alone for total body mass, fat-free mass, chest press and leg press one-repetition maximum, and the 30-second chair stand. It made no difference to knee extension or biceps curl.
A 2026 three-level meta-analysis in Frontiers in Nutrition by Yao and colleagues, covering 11 randomized trials in adults 60 and over, is more cautious. Strength improved with a Hedges’ g of 0.31, rated moderate certainty under GRADE, and the authors themselves call the effect small. Muscle mass and physical function did not reach statistical significance, at low and very low certainty. The authors add that their findings should not be extended to frail or sarcopenic older adults, who were not the people studied.
One structural point runs through all of it. In nearly every trial the comparison group was training too. Creatine was tested as an addition to training, never a replacement for it.
What it does not do
The NIH Office of Dietary Supplements, in its fact sheet on supplements for exercise and athletic performance, describes creatine as improving performance during repeated short bursts of high-intensity, intermittent activity, and as being of little value for endurance sports such as distance running.
A 2002 meta-analysis in the Journal of Family Practice by Dempsey and colleagues shows the same split inside one study set. Across 16 trials, bench press improved by 6.85 kilograms and squat by 9.76 kilograms. There was no difference for arm curls, none on cycle ergometer sprint peak power, and none on isokinetic dynamometer testing. Same supplement, different tests, different answers.
The kidney question is really two questions
These get collapsed constantly, and collapsing them produces a wrong answer in both directions.
What the controlled studies measured
A 2026 systematic review in the International Urology and Nephrology, by de Souza Almeida and colleagues at the Federal University of São Paulo, pooled 26 randomized trials covering 1,036 participants. Serum creatinine rose by a mean difference of 0.14 mg/dL. Glomerular filtration rate, when estimated from that creatinine, fell by 10.75 mL/min.
Then the same review looked at trials that measured filtration directly with chromium-51 EDTA clearance, which does not depend on creatinine at all. By that method the difference was plus 5.89 mL/min, with a confidence interval crossing zero. No change. Serum urea, albuminuria, proteinuria and urinary creatinine showed no differences either. The authors write that the findings “likely reflect altered creatinine metabolism rather than kidney injury, given the absence of changes when assessed using Cr-EDTA.” The review covered people with chronic kidney disease as well as healthy volunteers, and reported the same creatinine rise in its hemodialysis subgroup, alongside a fall in serum urea.
The mechanism is simple once stated. Creatine in muscle breaks down into creatinine. Laboratories estimate kidney filtration by measuring creatinine in blood, assuming a healthy person makes a fairly steady amount. Supply extra creatine and the person makes more creatinine, so the estimate shifts while the kidney keeps doing exactly what it was doing.
Two older studies anchor this. A 2013 randomized trial in the Journal of the International Society of Sports Nutrition, led by Lugaresi and Gualano, followed resistance-trained people on a high-protein diet for 12 weeks, with filtration measured by chromium-51 EDTA clearance. Nothing moved. A 1999 study in Medicine and Science in Sports and Exercise by Poortmans and Francaux compared people who had used creatine for 10 months to 5 years against controls and found no differences in creatinine, urea or albumin, or in their clearances.
Existing kidney disease is a separate question
Every source that addresses this says the same thing, and none says it casually. A 2004 review in the Journal of Herbal Pharmacotherapy by Yoshizumi and Tsourounis states that in people with a history of renal disease, or those taking medications that are hard on the kidneys, creatine may be associated with increased risk of renal dysfunction, and it documents a case report of acute renal failure in a 20-year-old man. A 2019 review in the Revista Médica de Chile by two hospital nephrologists reaches the same conclusion and adds the clinical consequence: because laboratories report estimated filtration from serum creatinine, an elevated creatinine can lead to over-diagnosing chronic renal failure.
That is the practical hazard for an ordinary person, and it is not a supplement hazard. It is a chart hazard. If a routine metabolic panel comes back with a creatinine at the top of the range and a filtration estimate that looks reduced, whether the person uses creatine changes what the number means. That is a conversation with the clinician who ordered the test, before anyone works up kidney disease. Medication interactions are covered in article 677.
No state bans selling creatine to minors, but two restrict a category
The answer is in the statutes, and it matches neither of the two things people usually say.
New York acted first. Senate bill S5823-C was signed on October 25, 2023 as Chapter 558 and took effect on the 180th day afterward, April 22, 2024. It bars selling, offering to sell, or giving away as a retail or wholesale promotion an over-the-counter diet pill or a dietary supplement for weight loss or muscle building to any person in the state under eighteen. The civil penalty is up to five hundred dollars.
California followed. Assembly Bill 2030 was signed on September 28, 2026 and uses the same structure: products labeled, marketed or otherwise represented for the purpose of achieving weight loss or building muscle cannot be sold to people under 18, in store or by delivery. Civil penalties run up to $500 per violation, sought by the attorney general, a county counsel or a city attorney. Under-18s with a prescription are exempt.
New Jersey has a bill pending: A 5487, introduced on September 14, 2026 by Assemblywoman Shanique Speight, with a civil penalty up to $750.
Where creatine appears
In neither enacted statute is creatine a banned ingredient. In New York it appears in a list of factors a court is directed to consider when deciding whether a product is marketed for weight loss or muscle building, alongside green tea extract, raspberry ketone, garcinia cambogia and green coffee bean extract. California’s law uses the same list the same way. The other factors are labeling, marketing claims about body weight, appetite, metabolism, muscle or strength, and how a retailer groups the product on a shelf.
So a container of plain creatine monohydrate sold without muscle-building claims is not obviously covered. A creatine product sold as a muscle builder plausibly is. No court has drawn the line, and the statutes do not draw it for them. Anyone saying creatine is banned for minors in these states is overstating the law; anyone saying the laws clearly exempt it is understating it. It is unresolved.
New York’s definition also carves out protein products: it excludes protein powders, protein drinks and foods marketed as containing protein. That exclusion has a catch, which article 340 takes up.
The law itself is being challenged
The Council for Responsible Nutrition, a supplement trade association, sued in the Southern District of New York in March 2024 on First Amendment grounds. The district court denied a preliminary injunction that April, the Second Circuit affirmed in November 2025, and rehearing was denied that December. On March 30, 2026, CRN petitioned the U.S. Supreme Court, arguing the statute is a content-based restriction on commercial speech. The Court denied the petition on October 5, 2026, leaving the Second Circuit’s ruling standing and the New York statute in force. That settles the First Amendment question in the Second Circuit but not nationally, so the framework California copied has survived its first constitutional test.
Professional bodies split, and the split tracks who pays
Two literatures describe the same evidence and reach different conclusions. The difference is visible in the author affiliations printed on the papers.
The International Society of Sports Nutrition position stand, published in 2017 and led by Richard Kreider, states that short and long-term supplementation is safe and well tolerated in healthy individuals and in patient populations from infants to the elderly, at intakes well above what most trials used and for as long as five years. It is the most-quoted safety sentence in creatine marketing.
Its author list, as printed, includes people affiliated with Vitargo Global Sciences, Post Active Nutrition, The Center for Applied Health Sciences, Supplement Safety Solutions, a contract research organization, and a law firm whose named author practices in the supplement industry. Those are disclosures the paper makes about itself. They are also what a reader needs before treating the sentence as neutral.
The clinical literature describes a much thinner record. A 2023 review in the Journal of Orthopaedics by Metzger and colleagues at Nationwide Children’s Hospital screened 9,393 articles and found 13 that studied creatine in a pediatric or adolescent population. Add the 13 together and you get 268 subjects. Their mean ages run from 11.5 to 18.2 years, and soccer players or swimmers account for 85 percent of the enrollment. The authors write: “The overall quality of the studies was poor, and there were no consistent findings regarding creatine supplementation and improvements in athletic performance.” No study, they add, was designed to address safety.
A 2017 review in Sports Health by Butts, Jacobs and Silvis says the safety of creatine supplementation has not been studied in children and adolescents, and that whether it improves performance in actual competition remains unknown.
The NIH Office of Dietary Supplements sits closer to the clinical side. Its fact sheet notes that an American Academy of Pediatrics review found protein, creatine and caffeine were the ingredients adolescents used most, with use rising with age, that much of the research involves young adults rather than adolescents, and that teenagers may use these products against the advice of pediatric and high school professional associations.
Both camps are looking at the same 268 subjects. One calls that reassuring, the other an evidence gap. Adolescent sports nutrition more broadly is covered in article 660.
Contamination is a category problem
Nothing here is specific to creatine, and the distinction matters.
A 2017 review in Nutrients by Martínez-Sanz and colleagues examined 23 analytical studies of sports supplements and reported contamination rates between 12 and 58 percent. A 2022 review in BioMed Research International pooled 50 studies covering 3,132 supplements and found undeclared substances in 875 of them, more than 28 percent, most often sibutramine and anabolic steroids.
The most useful number comes from an anti-doping program rather than a product survey. Fredrik Lauritzen at Anti-Doping Norway reviewed 18 years of national testing, 2003 through 2020. Of 192 analytical anti-doping rule violations, athletes blamed a supplement in 49 cases, 26 percent, and evidence supported the claim in 27, or 14 percent of all analytical violations. The products causing the trouble were overwhelmingly multi-ingredient pre-workout formulas, 20 cases, and fat burners, 4.
Risk concentrates in products with long ingredient lists, not in single-ingredient powders. What third-party certification marks do and do not cover is handled in article 326.
The brain claims are at an earlier stage
Creatine’s cognitive research is in a different evidence tier from its muscle research, and the gap is wide.
A 2023 meta-analysis in Nutrition Reviews by Prokopidis and colleagues pooled eight randomized trials on memory in healthy people. Memory improved with a standardized mean difference of 0.29, confidence interval 0.04 to 0.53, with substantial heterogeneity. Split by age, adults 66 to 76 showed 0.88, while participants aged 11 to 31 showed 0.03, which is nothing.
A 2024 analysis in Frontiers in Nutrition by Xu and colleagues, covering 16 trials and 492 participants, found memory improved by a standardized mean difference of 0.31, rated moderate certainty under GRADE. Overall cognitive function and executive function did not improve significantly.
A 2026 systematic review in Nutrition Reviews by Marshall and colleagues looked specifically at older adults. Of the six studies it found, only two were double-blind supplementation trials; four were cross-sectional and estimated creatine intake from dietary recall. One rated good on methodological quality, two fair and three poor.
And a 2024 systematic review in Behavioural Brain Research by Terry McMorris and colleagues states its conclusion in its title: the research fails to support the theoretical basis for an effect on cognition. Supplementation does raise brain creatine, the authors say, but to a limited extent.
One moderate-certainty signal for memory in older adults, surrounded by low-certainty findings and a systematic review questioning the mechanism, is a fair summary. It is not the same kind of claim as the strength data and should not be presented as one.
Telling a strong creatine claim from a weak one
Four questions separate the evidence from the marketing. Creatine is a good place to practice, because there is real data underneath to check against.
Which outcome is claimed? Short, hard, repeated efforts combined with resistance training is the claim with evidence behind it. Endurance, fat loss on its own, general energy and mental sharpness rest on thinner data.
Compared with what? In almost every trial the control group was also training. A claim that drops the training has dropped the control group.
Who was in the study? Twenty of 23 trials in the 2024 strength meta-analysis enrolled only men. The entire adolescent evidence base is 268 subjects.
Who wrote it, and where do they work? Affiliations are printed on the first page of every paper. In sports nutrition, industry affiliation is the norm rather than the exception, so reading the list is routine rather than cynical.
What holds up, and where the gaps are
Stated conservatively: in adults under 50, mostly men, adding creatine to a resistance training program produced about a kilogram more lean mass and measurable strength gains over roughly three months, with a smaller effect when muscle was imaged directly. In adults over 60, strength improved modestly at moderate certainty, while muscle mass and physical function did not reach significance. In healthy people, trials that measured kidney filtration directly found no sign of injury. In people with existing kidney disease or taking medications that stress the kidneys, every source that addresses the question urges caution.
And no US jurisdiction bans the sale of creatine to minors. Two states restrict a marketing category in which creatine appears only as one factor a court may weigh.
If you carry one thing out of this, make it the creatinine problem. A person using creatine who has a routine kidney panel drawn can end up with a filtration estimate that looks worse than their kidneys are. The number on the printout is not the thing to act on. Whether the clinician reading it knows about the supplement is.
Sources
- National Institutes of Health, Office of Dietary Supplements. “Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals.” ods.od.nih.gov
- New York State Senate. “Senate Bill S5823, 2023-2024 Legislative Session (Chapter 558 of 2023).” nysenate.gov
- Epstein Becker & Green. “States Further Legislation to Restrict Sale of Weight Loss, Muscle Building Products to Minors.” ebglaw.com
- Haynes and Boone, LLP. “New California Law Bans Sale of Diet Pills and Certain Supplements to Minors.” haynesboone.com
- Council for Responsible Nutrition. “CRN Petitions U.S. Supreme Court to Review New York Law Restricting Supplement Sales Based on Marketing Claims.” crnusa.org
- Journal of Strength and Conditioning Research (PubMed). “Desai I et al. "The Effect of Creatine Supplementation on Resistance Training-Based Changes to Body Composition: A Systematic Review and Meta-analysis." 2024. DOI: 10.1519/JSC.0000000000004862.” doi.org
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- Frontiers in Nutrition (PubMed). “Yao L, Yang D, Gao J. "Effects of resistance training combined with creatine supplementation on muscle strength, physical function, and muscle mass in older adults." 2026. DOI: 10.3389/fnut.2026.1919884.” doi.org
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- International Urology and Nephrology (PubMed). “de Souza Almeida A et al. "Impact of creatine supplementation on kidney health: a systematic review and meta-analysis." 2026. DOI: 10.1007/s11255-026-05287-x.” doi.org
- Journal of the International Society of Sports Nutrition (PubMed). “Lugaresi R, Gualano B et al. "Does long-term creatine supplementation impair kidney function in resistance-trained individuals consuming a high-protein diet?" 2013. DOI: 10.1186/1550-2783-10-26.” doi.org
- Medicine and Science in Sports and Exercise (PubMed). “Poortmans JR, Francaux M. "Long-term oral creatine supplementation does not impair renal function in healthy athletes." 1999. DOI: 10.1097/00005768-199908000-00005.” doi.org
- Journal of Herbal Pharmacotherapy (PubMed). “Yoshizumi WM, Tsourounis C. "Effects of creatine supplementation on renal function." 2004. PMID 15273072.” pubmed.ncbi.nlm.nih.gov
- Revista Medica de Chile (PubMed). “Vega J, Huidobro EJP. "Effects of creatine supplementation on renal function." 2019. DOI: 10.4067/S0034-98872019000500628.” doi.org
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- Journal of the International Society of Sports Nutrition (PubMed). “Kreider RB et al. "International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine." 2017. DOI: 10.1186/s12970-017-0173-z.” doi.org
- Nutrients (PubMed). “Martinez-Sanz JM et al. "Intended or Unintended Doping? A Review of the Presence of Doping Substances in Dietary Supplements Used in Sports." 2017. DOI: 10.3390/nu9101093.” doi.org
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- Frontiers in Sports and Active Living (PubMed). “Lauritzen F. "Dietary Supplements as a Major Cause of Anti-doping Rule Violations." 2022. DOI: 10.3389/fspor.2022.868228.” doi.org
- Nutrition Reviews (PubMed). “Prokopidis K et al. "Effects of creatine supplementation on memory in healthy individuals: a systematic review and meta-analysis of randomized controlled trials." 2023. DOI: 10.1093/nutrit/nuac064.” doi.org
- Frontiers in Nutrition (PubMed). “Xu C, Bi S, Zhang W, Luo L. "The effects of creatine supplementation on cognitive function in adults: a systematic review and meta-analysis." 2024. DOI: 10.3389/fnut.2024.1424972.” doi.org
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