What does creatine monohydrate do for your health?
For strength and muscle mass during high-intensity training, creatine monohydrate (3 to 5 g per day) has the strongest evidence base of any dietary supplement. In endurance sports it offers no benefit, and if you have a kidney condition you should discuss its use with your doctor first.
Creatine monohydrate has the strongest evidence base for short-duration, high-intensity exercise: lean muscle mass increases, maximum strength rises, and you can perform more total work. This effect has been found repeatedly across multiple studies. The dose commonly used in research is 3 to 5 grams per day, or 0.1 grams per kilogram of body weight.
Recovery after hard training may also be faster: muscle damage appears to be reduced and strength loss recovers more quickly. This evidence is promising but somewhat less convincing than the evidence for direct strength gains. In endurance sports the picture is mixed; in sports where a small increase in body weight affects your pace, creatine can even be a disadvantage.
For older adults there are indications that creatine helps preserve muscle mass, possibly also supporting bone health and perhaps cognitive function. The evidence here is promising but requires further research. There are also early indications that creatine may protect the brain after injury and can ease symptoms of sleep deprivation, but in humans this has only been studied in small trials so far.
Creatine does not cause kidney damage in healthy people at the recommended dose. Even at high doses of 30 grams per day over 5 years it proved safe. If you have an existing kidney condition, discuss its use with your doctor, as the evidence for that group is more limited. The stories about dehydration and muscle cramps are not supported by research. Whether creatine causes hair loss is unclear: one study observed a rise in a hormone that can promote baldness, but direct evidence for hair loss is lacking. Any weight gain that does occur is due to increased fluid in the muscles and greater muscle mass, not fat.
Creatine monohydrate is the most extensively studied form and performs no worse than more expensive alternatives. One caveat about the available literature: most review studies have been written by researchers with financial ties to creatine manufacturers, in particular a German chemical company. The positive findings are consistent, but independent research is underrepresented in the source material.
This answer draws on several large reviews covering dozens of studies, including studies in which participants were randomly assigned to receive creatine or a placebo. The evidence is strongest for muscle strength and safety in healthy adults. For the brain, cognition in older adults, and recovery, the evidence is more limited and some of the indications come from smaller studies. An important caveat: most reviews have been written, at least in part, by authors with financial ties to creatine manufacturers; independent confirmation is partially lacking.