Is creatine safe for teenagers? The evidence is thin, not alarming

Nobody has properly tested whether creatine is safe for teenagers. A 2021 review of creatine use in children and adolescents found that the trials which do exist in teenage athletes generally improved performance and reported no adverse events, while noting that much less is known about this age group than about adults [3]. A 2018 clinical review in a sports medicine journal was blunter: the safety of creatine supplementation has not been studied in children and adolescents [4].

The kidney question is the one parents raise most. It starts with a blood test rather than a case of kidney damage. Creatine breaks down into creatinine, a waste product doctors measure in blood to estimate how well the kidneys are filtering, so taking more creatine leaves more creatinine to clear and the number can drift up while filtration is unchanged [2]. A placebo-controlled trial built to hunt for side effects gave 175 adults 10 grams a day for about ten months and found no rise in blood urea, a second kidney marker, and fewer people with traces of protein in their urine at the end than at the start, about 2 in 100 rather than about 5 in 100 [8].

Side effects in that trial were close to identical in both groups. Nausea was reported by 23 in 100 taking creatine against 24 in 100 on the dummy powder, stomach discomfort by 19 against 18, and diarrhoea by 35 against 24 [8]. Swollen limbs showed up more often in the creatine group after two months, probably water retention, and three people stopped because of severe diarrhoea or nausea, which cleared up once they did [8].

The one placebo-controlled trial that recruited young athletes did not look at kidneys at all. Nineteen elite footballers aged 16 to 21 took creatine or a dummy powder for eight weeks, and the creatine group's airway readings moved the wrong way: a marker of airway inflammation rose in them and fell in the placebo group, and after a dry-air breathing challenge the air they could blow out in one second dropped by about 10%, against about 4% on placebo [13]. With nineteen players, chance could explain differences that size. The authors said only that they could not rule out an effect, and it looked stronger in the 15 players who had allergies [13].

The closest thing to long-term data in young women comes from 71 youth and professional footballers who took creatine across a 32-week season. Researchers tracked 18 blood markers. Every marker except creatine phosphokinase, an enzyme that leaks out of working muscle, stayed inside normal ranges, kidney and liver measures included, and the researchers put that one marker's movement down to training load rather than the supplement [7].

Creatine is not a foreign chemical. The body makes roughly half of what it uses and the rest arrives in meat and fish. Inside muscle it is stored as phosphocreatine, a fast-access store that hands a phosphate back to spent energy molecules so a muscle can keep contracting hard for a few more seconds [1][2]. Supplements work by topping those muscle stores up, which is why measured gains sit in short maximal efforts such as sprints and heavy lifts rather than in endurance [1][4].

That chemistry is also why the kidney rumour survives. Creatine is broken down steadily into creatinine, the kidneys clear it into urine, and a raised blood creatinine reading is one of the standard signs a doctor uses to suspect a kidney is struggling. More creatine in means more creatinine to clear, so the reading moves for a reason that has nothing to do with damage [2].

Nobody has identified a mechanism specific to growing bodies. The worry about teenagers comes from absence rather than from a known biological route to harm: adolescents were barely ever the population these safety studies recruited [3][4], and the one trial that did recruit them was measuring airways, where it offered no mechanism for what it saw [13].

The gaps are specific.

• Almost nothing covers children under about 16. The youth trial recruited players aged 16 to 21 [13], so a question about a 13 or 14 year old is a question the research has not answered.
• The young participants were elite athletes in academy and professional football squads [7][13], not ordinary teenagers training at a school gym.
• The long placebo-controlled trial that found no kidney signal ran in adults averaging 58 years old who had a neurodegenerative disease, amyotrophic lateral sclerosis [8]. What it says about kidney markers does not transfer cleanly to a healthy 15 year old.
• The season-long study in young female footballers had no group taking a dummy powder [7], so it can report that blood markers stayed normal but cannot attribute that to creatine.
• None of these studies tested what sits on a shop shelf. Purity, labelling accuracy and contamination of commercial products were not measured.

The airway result in young footballers shows how unsettled this is: one trial, nineteen players, a difference chance could account for, and no attempt yet to repeat it [13].

A parent of a 15 year old who has started lifting and wants creatine is not weighing a proven risk against a proven benefit. They are deciding without evidence, which is a different problem. A 2025 review of nutrition for adolescent athletes names creatine and energy drinks as the supplements that warrant caution at this age, and argues for covering needs from food first [5], partly because a teenager training hard is far more likely to be short on total calories, protein, iron, calcium or vitamin D than to be short on anything sold as a performance aid [5]. The questions a doctor can help with are whether those basics are in place, and whether something specific to this child, such as a kidney condition or diagnosed asthma given the airway trial [13], is a reason to leave it alone.