Creatine monohydrate is one of the most studied sports supplements available, and most research confirms it’s safe for healthy adults. But it does come with real downsides, ranging from predictable water weight gain to digestive discomfort that affects a surprisingly high percentage of users. Some concerns, like kidney damage and muscle cramps, turn out to be largely unfounded. Others, like the quality of what you’re actually swallowing, deserve more attention than they get.
Digestive Problems Are Common
Gastrointestinal symptoms are the most frequent complaint among creatine users, and the numbers are higher than most people expect. In a 28-day supplementation trial, 79.2% of all participants reported at least one unwanted digestive symptom, with bloating, stomach discomfort, water retention, and puffiness topping the list. Women were affected at a slightly higher rate of 81%.
The dose matters significantly. Participants taking a standard 5 grams per day reported water retention (50%), bloating (42%), and puffiness (42%) as their most common issues. Those on a loading dose of 20 grams per day fared worse: 67% experienced bloating, 58% had stomach discomfort, and 33% developed diarrhea. Researchers believe creatine’s poor solubility, roughly 18 milligrams per milliliter of water, is partly to blame. At higher doses, the intestines can’t absorb it fast enough, and undissolved creatine sitting in the gut draws in water and causes irritation.
If you’re considering a loading phase to saturate your muscles faster, these numbers suggest starting with a lower daily dose of 3 to 5 grams may be worth the slower ramp-up.
Water Weight Gain Is Real
The weight gain most people notice in the first few weeks of creatine use is almost entirely water. Creatine pulls water into muscle cells through an osmotic process: as creatine enters the cell alongside sodium, water follows to maintain balance. An eight-week trial that included a five-day loading phase found that the creatine group gained about 3% more body mass than the placebo group, with intracellular water increasing by 9.2% compared to just 1.6% in the placebo group.
This water is stored inside the muscle cell, not under the skin. Over time, this cell swelling may actually stimulate muscle protein synthesis, which is part of how creatine supports muscle growth. But if you’re tracking your weight for a sport with weight classes, or you simply care about the number on the scale, expect an initial jump of a few pounds that doesn’t reflect fat gain. For some people, the puffiness in their face or midsection is cosmetically bothersome enough to stop supplementing.
The Hair Loss Question
The idea that creatine causes hair loss traces back to a single 2009 study on 20 college-aged rugby players. After seven days of a high loading dose (25 grams per day), their levels of DHT, a hormone linked to male pattern baldness, rose by 56%. After two weeks on a 5-gram maintenance dose, DHT remained 40% above baseline. Testosterone itself didn’t change, suggesting creatine may have accelerated the conversion of testosterone into its more potent form.
That study generated enormous concern, but no subsequent research has replicated the finding. A 2025 randomized controlled trial specifically designed to test this question tracked 45 resistance-trained men over 12 weeks, measuring both hormone levels and actual hair follicle health using specialized imaging. The result: no significant differences in DHT levels, the DHT-to-testosterone ratio, or any hair growth parameter between the creatine and placebo groups. The researchers concluded their findings provided “strong evidence against the claim that creatine contributes to hair loss.”
If you’re already genetically predisposed to male pattern baldness, the theoretical concern isn’t zero, but the current weight of evidence doesn’t support avoiding creatine for this reason.
Kidney Concerns Are Mostly a Myth
Creatine breaks down into creatinine, a waste product filtered by the kidneys. Because doctors use creatinine levels as a marker for kidney function, creatine users often get flagged with artificially high readings on routine blood work. This has fueled a persistent belief that creatine damages the kidneys.
Controlled studies don’t support this. A 12-week trial measuring actual kidney filtration rates (not just creatinine levels) in postmenopausal women found no change whatsoever between the creatine group and the placebo group. The filtration rate stayed essentially identical before and after supplementation. Multiple other studies in healthy adults have reached the same conclusion.
The important caveat is the phrase “healthy adults.” If you already have reduced kidney function or kidney disease, adding any extra filtering burden is a different calculation. The existing safety data applies to people whose kidneys are working normally.
Dehydration and Cramping: Not What You’d Expect
Surveys of athletes who use creatine show that 14% to 25% report feeling dehydrated and up to 27% report muscle cramps. But these self-reports don’t hold up under controlled conditions. When researchers actually measure hydration status and body temperature regulation during exercise in hot and humid environments, creatine users show no impairment compared to non-users.
In fact, the data leans in the opposite direction. A comprehensive review published in Frontiers in Nutrition rated the evidence that creatine causes dehydration as “not supported” with a Grade I (strong) evidence rating. For muscle cramps, the evidence was similarly unsupportive, with some studies suggesting creatine may actually reduce cramp incidence during exercise. The likely explanation for the survey results is that athletes who train harder, take more supplements, or exercise in challenging conditions are more prone to cramps and dehydration regardless of creatine use.
Supplement Purity Varies Widely
One underappreciated downside has nothing to do with creatine itself but with what else might be in the container. Creatine is manufactured through chemical synthesis, and cheaper production methods leave behind contaminants. The most common impurities include creatinine (a harmless but useless byproduct), dicyandiamide, and compounds called dihydrotriazine derivatives.
Dicyandiamide is the more concerning of these. While the body has detoxification systems that can convert it into less harmful substances, stomach acid can also convert it into hydrogen cyanide, a toxic compound. An alternative low-cost manufacturing route avoids dicyandiamide but can generate thiourea, which the International Agency for Research on Cancer classifies as a possible human carcinogen.
This doesn’t mean creatine supplements are dangerous, but it does mean quality matters. Products that carry third-party testing certifications are more likely to have gone through adequate purification. Bargain-bin creatine from unknown manufacturers carries a higher risk of these impurities.
Not Recommended for Adolescents
The American Academy of Orthopaedic Surgeons states that children and adolescents younger than 18 should not take creatine supplements. The reason isn’t that studies have found harm in young people, but that long-term safety research in bodies that are still growing simply doesn’t exist. The same recommendation applies to pregnant and nursing women. Most of the reassuring safety data comes from studies on adults, and extrapolating those results to developing bodies involves too many unknowns.