Creatine is a compound the body makes from three amino acids and stores mostly in muscle, where it buffers the energy supply for short, hard efforts. Meat and fish contain it; a supplement raises the muscle store beyond what diet alone reaches.

It is unusual on this site for two reasons. First, the evidence base is large and old enough that the arguments are about the size of the effect, not whether there is one. Second, almost every trial used the same cheap form, creatine monohydrate, so the usual problem of comparing different products barely arises.

The claims to watch are the newer ones. Creatine for the brain, for mood, for aging, for women specifically: each has some trials behind it now, and each is at a much earlier stage than the strength literature it borrows credibility from.

Muscle regenerates its immediate energy currency, ATP, from phosphocreatine during the first seconds of intense effort. Raising the phosphocreatine store means a few more seconds of near-maximal work before fatigue, and faster recovery between efforts. More total work in training is the proposed route to more muscle over weeks.

The same chemistry runs in the brain, which is metabolically expensive and keeps its own creatine pool. The cognitive hypothesis is that supplementation raises that pool, and that the benefit shows where the brain is under strain: sleep loss, aging, low dietary intake. That is a reasonable hypothesis with early support, not a settled mechanism.

Creatine also draws water into muscle cells. Part of the early weight gain on it is that water, which is why scale weight in the first weeks says little about muscle.

Strength and lean mass: established, and small. A 2022 meta-analysis of 35 randomized trials in nearly 1,200 people found creatine added about two thirds of a kilogram of lean mass overall, and about a kilogram when combined with resistance training, with no significant effect without training. A 2024 analysis restricted to adults under 50 put the training-combined gain at just over a kilogram of lean mass, with a small reduction in body fat. Those are real, repeatable numbers. They are also modest, and they depend on the training being there.

Older adults. A meta-analysis of ten trials in older women found creatine with resistance training improved upper-body strength, with lower-body gains appearing only in trials of six months or longer. The sex difference is a recurring theme: pooled data show men gaining more lean mass than women on creatine, for reasons not yet understood.

Memory and cognition: promising, early. A 2023 meta-analysis of eight randomized trials found a small overall improvement in memory in healthy people, driven almost entirely by adults aged 66 to 76, with no effect in the young. A 2024 analysis of sixteen trials found moderate-certainty evidence for memory and low-certainty evidence for processing speed and attention, and no effect on overall cognition or executive function. The trials are small and the measures vary, so this is a signal worth following rather than a result to rely on.

Creatine monohydrate has the longest safety record of any supplement on this site. Across decades of trials, the consistent findings are weight gain from water retention and, at higher single doses, stomach upset. Claims that it harms healthy kidneys have not held up in trials that measured kidney function, though it does raise serum creatinine, a kidney marker, which can alarm a clinician who does not know a person is taking it. Tell your doctor before a blood test.

What is not known is the same thing that is not known for every supplement: effects over decades, in people with existing kidney disease, and in pregnancy, none of which the trials covered. Products other than plain monohydrate, sold as better absorbed or more stable, mostly lack trials of their own.

Creatine is sold as a dietary supplement in the United States, the European Union, the United Kingdom and most other markets. It is not a medicine anywhere and has never been through a regulator's review of its claims. It is not banned in sport; the World Anti-Doping Agency does not list it.

Because it is a supplement, no regulator checks what is in a given tub before it is sold. Third-party testing programs exist for that reason, and the difference between a tested and an untested product is the difference between knowing and assuming.