Creatine occupies a strange position in public perception: one of the most thoroughly researched supplements ever sold, with hundreds of trials across four decades, and simultaneously one of the most mythologised. Ask the internet about its side effects and you will collect kidney damage, hair loss, dehydration, cramps and aggression, mostly asserted, rarely referenced. The trial literature tells a much shorter and duller story, and dull is exactly what you want from something taken daily. Here is what the evidence actually supports, what it refutes, and where genuine caution belongs.
What creatine is doing in the first place
Creatine is not a stimulant or a hormone; it is a naturally occurring compound your liver and kidneys synthesise daily, stored mostly in muscle as a rapid-recycling energy reserve for short, intense efforts. Supplementation simply tops the tank up by around 20 to 40%, which is why its benefits, a little more output in repeated hard efforts, better training quality, modest gains in strength and lean mass over time, are real but incremental. This matters for the side-effect conversation: you are raising the level of something already present in every cell, not introducing a foreign pathway. Half the reputational trouble comes from creatinine, the similarly named breakdown product used to estimate kidney function, a confusion worth untangling early because it sits underneath the single most repeated safety claim against the supplement.
The genuine side effects
Two effects survive contact with the trial data. The first is water weight. Creatine pulls water into muscle cells alongside it, and the scales typically rise by one to two kilograms over the first weeks. This is intracellular water in muscle, not fat and not bloating in the digestive sense, and it partly underwrites the performance benefit, but anyone tracking weight for other reasons, including during weight loss treatment, should know the jump is coming and what it is. The second is digestive upset, nausea, cramping or loose stools, which appears almost exclusively at large single doses, the classic 20g-a-day loading protocols, and largely vanishes when doses stay at 3 to 5g or are split through the day. Beyond these, large reviews and long-term trials, some running years in clinical populations, report side-effect rates on creatine that look remarkably like placebo.
The kidney question, answered properly
The persistent kidney worry rests on that naming confusion. Supplementing creatine raises creatinine, the marker blood tests use to estimate kidney function, because more creatine turnover means more breakdown product. The estimate shifts; the kidneys themselves are doing nothing different. Studies that measure kidney function directly, rather than estimating it from creatinine, consistently find no damage in healthy users at standard doses, including in trials lasting years. Position stands from the International Society of Sports Nutrition state plainly that creatine at recommended doses is safe for healthy individuals. The honest caveats: people with existing kidney disease were not the population in those trials and should involve their clinician before supplementing, and it is worth telling any doctor interpreting your blood results that you take creatine, so a raised creatinine is read correctly rather than triggering an unnecessary investigation.
The myths, measured against trials
Hair loss is the stickiest modern claim, and it traces to a single 2009 study in rugby players that found raised DHT, the hormone involved in pattern hair loss, on a loading dose. The finding has not been replicated; subsequent studies measuring hormones on creatine found no meaningful DHT change, and no trial has ever measured actual hair loss on creatine. For someone already predisposed and anxious, avoiding creatine is an understandable personal choice, but the evidence as it stands does not support the fear. Dehydration and cramping claims have been tested directly, and trials in athletes, including in heat, found no increase in cramps or dehydration on creatine; some found fewer such events, plausibly because better-hydrated muscle cells are the opposite of a dehydration risk. Weight gain beyond the water effect, mood changes and aggression claims have no controlled evidence behind them at all. The pattern is familiar from supplement folklore generally: an early small signal or a plausible-sounding mechanism, repeated for a decade after the follow-up studies quietly failed to confirm it, and kept alive by the fact that debunkings never travel as far or as fast as the original scare.
Who should be cautious, and how to take it sensibly
The caution list is short and specific. Anyone with kidney disease, a single kidney or conditions affecting renal function: clinical advice first, always. People on medicines that stress the kidneys, including long-term NSAIDs, deserve the same conversation. Pregnancy and breastfeeding lack good supplementation data, so the default is to abstain. Adolescents can use creatine under sensible supervision according to sports-medicine consensus, but supplements in teenagers deserve adult oversight generally. For everyone else, the sensible protocol is also the comfortable one: 3 to 5g of creatine monohydrate daily, any time of day, with or without food, skipping the loading phase entirely since stores saturate within three to four weeks at maintenance doses anyway. Choose plain monohydrate from a brand with third-party testing; it is the form all the safety evidence describes, and the exotic alternatives cost more to deliver less data. Drink normally, expect a kilogram or so of benign water weight, and let the boring evidence be the point. For the dosing detail, see our guide to how much creatine to take per day, and for women specifically, our article on what creatine does for women.
