Most healthy adults can take creatine without problems. It’s one of the most studied supplements in sports nutrition, with a strong safety record at recommended doses (3 to 5 grams per day). But certain groups of people have legitimate reasons to avoid it or use it only under medical supervision, ranging from those with impaired kidney function to pregnant women to people with bipolar disorder.
People With Kidney Disease
Your kidneys filter creatinine, the waste product your body creates when it breaks down creatine. In healthy kidneys, this extra filtering load is no big deal. But if your kidneys are already struggling, adding supplemental creatine increases the workload on an organ that can’t keep up.
A large clinical trial studying creatine in Parkinson’s disease patients illustrates the concern. The study’s safety board flagged rising creatinine levels and falling estimated kidney filtration rates (eGFR) in participants. Researchers changed their entry criteria to exclude anyone with an eGFR below 50, and they pulled participants off creatine entirely if their eGFR dropped below 30 or their creatinine levels doubled from baseline. These thresholds correspond roughly to moderate and severe kidney disease.
There’s also a practical problem: creatine supplementation raises serum creatinine levels on its own, independent of actual kidney damage. This means the standard blood test doctors use to monitor kidney function becomes unreliable. For older adults or anyone already being tracked for kidney problems, this masking effect can hide real deterioration. If you have any stage of chronic kidney disease, or if your doctor has flagged your kidney function as borderline, creatine is not worth the risk.
Pregnant and Breastfeeding Women
Creatine naturally appears in breast milk, supplying roughly 9% of an infant’s daily needs. But no human studies have measured what happens to milk creatine levels when a mother takes supplemental doses. The safety gap here is straightforward: nobody has tested it, so nobody can confirm it’s safe.
There’s also a downstream concern for infants. Creatine converts to creatinine in both the mother’s and baby’s body, which could raise the infant’s serum creatinine. That would throw off any assessment of the baby’s kidney function, a problem for newborns who may already be monitored closely. The National Institutes of Health’s LactMed database recommends avoiding creatine supplementation during breastfeeding unless a healthcare professional specifically prescribes it. The same caution applies during pregnancy, where the absence of clinical safety data makes supplementation an unnecessary gamble.
People With Bipolar Disorder
Creatine plays a role in brain energy metabolism, which is why researchers have explored it for conditions like depression. But for people with bipolar disorder, that same energy-boosting effect may tip the balance toward mania. In an open-label clinical trial, two patients with bipolar disorder developed hypomania or full mania after about three weeks of taking 3 to 5 grams of creatine daily.
Two cases isn’t a large evidence base, but it’s notable because almost no research has directly examined creatine in bipolar patients since. The mechanism is plausible: creatine increases the availability of cellular energy in the brain, and manic episodes are associated with heightened neural activity. Until controlled studies clarify the risk, people with bipolar disorder should treat creatine as a potential trigger.
Older Adults on Kidney-Monitored Medications
This group often gets overlooked. Many medications commonly prescribed to older adults, including certain blood pressure drugs and anti-inflammatories, require periodic kidney function monitoring through creatinine blood tests. If you’re taking creatine supplements, those tests will read artificially high, potentially triggering unnecessary medication changes, additional testing, or genuine kidney problems going undetected.
The Parkinson’s disease trial made this exact tradeoff explicit. Researchers noted that “the loss of the reliability of serum creatinine as a marker of kidney function is a likely adverse consequence of creatine use in clinical practice with older adults.” If you’re over 60 and on multiple medications, the interference with routine blood work alone is a reason to skip creatine, even if your kidneys are currently healthy.
What About Diabetes?
This one is more nuanced than a simple “avoid it.” Creatine doesn’t appear to be dangerous for people with type 2 diabetes, and some evidence suggests it could actually help. One small study in recently diagnosed type 2 diabetes patients found that 6 grams of creatine daily for five days lowered blood glucose levels about as effectively as metformin. Larger studies combining creatine with exercise training showed reductions in glycated hemoglobin (HbA1c), a key marker of long-term blood sugar control.
The caution is about drug interactions and blood sugar unpredictability. If creatine is lowering your glucose on top of your diabetes medication, you could end up with blood sugar that drops too low, especially during or after exercise. This doesn’t mean people with diabetes should never use creatine, but it does mean they shouldn’t start it without coordinating with whoever manages their blood sugar.
What About Liver Disease?
Despite lingering concerns, creatine does not appear to harm the liver. A large cross-sectional study of U.S. adults aged 12 and older found no difference in rates of liver fibrosis, cirrhosis, or fatty liver disease between people consuming less than 1 gram of creatine per day and those consuming more than 2 grams. After adjusting for age, gender, BMI, total calorie intake, and alcohol use, higher creatine intake did not increase the risk of any liver condition. If you have liver disease, creatine isn’t specifically contraindicated based on current evidence.
What About Dehydration and Cramping?
A persistent belief holds that creatine pulls water into your muscles and leaves the rest of your body dehydrated, causing cramps. The logic sounds reasonable: creatine is osmotically active, meaning it draws water into cells. In theory, during heavy sweating, that trapped intracellular fluid could leave you short on extracellular water, disrupting electrolyte balance.
In practice, experimental and clinical research doesn’t support this. Studies have not validated the idea that creatine causes dehydration or muscle cramping, even during exercise in hot conditions. If you take diuretics (water pills) for blood pressure or another condition, the combination with creatine hasn’t been shown to be dangerous, but staying well-hydrated is still common sense when you’re on any medication that affects fluid balance.
Adolescents and Teens
Most sports medicine organizations and pediatric groups have historically urged caution about creatine use in people under 18, not because of documented harm, but because of limited research in younger populations. The concern is partly physiological (developing bodies may respond differently) and partly practical (teens may not follow dosing guidelines carefully or may combine creatine with other supplements). While short-term studies in adolescents haven’t revealed serious safety issues, the conservative position remains that young athletes should focus on nutrition and training before reaching for supplements.