We grade every benefit. Proven means multiple controlled trials and pooled analyses agree. Probable means the studies point one way but are small or come from few groups. Promising means early data worth watching, not yet worth relying on.
Strength and power Proven
This is the benefit creatine is famous for, and it is as solid as sports-nutrition evidence gets. Pooled analyses of resistance-training studies consistently find that adding creatine produces greater gains in maximal strength than training alone, with typical improvements of 5 to 15% in one-rep-max lifts and in the number of repetitions performed at a given load.
The mechanism is simple. Phosphocreatine is the fastest way muscle regenerates ATP during efforts lasting up to about ten seconds, and the body burns this "clean" fuel before it switches to glycolysis, which produces the acid by-products that make muscles burn. A fuller store means longer on clean fuel, slightly more work per set, and over weeks of training that extra work compounds. Effects are largest in activities built from repeated short bursts: weight training, sprinting, jumping, rowing and interval work, and team sports such as football and rugby.
Lean mass and fat Proven
Creatine increases lean mass through two routes. In the short term, water moves into muscle cells alongside creatine, and the swelling itself appears to act as a growth signal. Over the longer term, the additional training volume creatine permits, together with a measurable reduction in protein breakdown, produces genuine muscle. Reviews put the extra lean mass from creatine plus training at roughly 1 to 2 kg over eight to twelve weeks, of which about half is skeletal muscle and the rest water and connective tissue.
Creatine does not burn fat directly, but pooled analyses report a small reduction in fat mass with creatine plus training, in women as well as men, most plausibly because more lean tissue raises energy expenditure. It will not stop weight loss in a calorie deficit, though the water gain can mask fat loss on the scales for a few weeks.
Vegetarians and vegans Proven
Dietary creatine comes almost entirely from meat and fish, so people on plant-based diets have muscle creatine stores around 20 to 30% lower than omnivores. When they supplement, they see larger increases in muscle creatine and larger improvements in performance, and the cognitive studies show the biggest effects in this group too. Supplemental monohydrate is synthetic and vegan, which makes it one of the few supplements with a clear case for plant-based athletes. Rare genetic disorders of creatine synthesis also require supplementation, under medical care.
Recovery and rehab Probable
Several trials report lower markers of muscle damage and inflammation after hard exercise in people taking creatine, and a short high-dose course before very long endurance events has reduced post-race inflammatory markers. Creatine is not an anti-inflammatory in the way a painkiller is; it appears to reduce the damage in the first place and keep phosphocreatine topped up between sessions.
The rehab angle is more interesting. Creatine helps preserve muscle and strength during periods of immobilisation, such as after injury or surgery, and speeds the regain of training volume afterwards. In one crossover-style study, volume rose on creatine, fell back to placebo levels about four weeks after stopping, and rebounded quickly on restarting. For anyone returning from injury, that is a useful lever.
Healthy ageing Probable
Muscle loss with age is one of the strongest predictors of frailty, falls and loss of independence. In older adults who lift weights, creatine reliably improves gains in strength and lean mass, and the outcomes that improve most are the functional ones: rising from a chair, climbing stairs, grip strength. Some researchers suggest a slightly higher dose after 50, around 7 to 8 g, because lower-body stores tend to be more depleted. Without resistance training the benefit largely disappears, so creatine is an addition to strength work, not a substitute.
Bone Probable
This is newer and more specific than the marketing suggests. The lowest dose that has shown any bone effect is around 8 g a day, and the effective range in the literature is 8 to 12 g, always combined with resistance training. The key trial gave postmenopausal women roughly 0.14 g per kilogram a day for two years alongside supervised lifting and found that creatine slowed the rate of bone loss at the hip and helped preserve bone structure. It did not increase density, and no study has shown a bone benefit from creatine without exercise. The proposed mechanism is that creatine fuels bone-building cells while damping bone-resorbing ones. Most of the data comes from one research group, so we grade it probable rather than proven. It is not a treatment for osteoporosis.
Creatine for women Proven
Creatine works in women exactly as it does in men, and the average water gain is smaller because it scales with muscle mass. The dose is the same. Recent research has looked at life stages: oestrogen is involved in the enzymes that make creatine, which offers a mechanism for why perimenopausal and postmenopausal women may benefit more, and it is this group that the bone research targets. One small trial in young female athletes found around an hour more sleep on training days with 5 g a day, which nobody has yet explained or replicated. The idea that creatine makes women "bulky" has no basis; the muscle it helps build is the muscle you train for.
Endurance sport Promising
Creatine adds little to steady-state endurance and, because it adds a kilogram or so of mass that must be carried and oxygenated, it may marginally lower relative aerobic capacity. It does help surges, sprint finishes, hill repeats and interval sessions, and it may reduce inflammation after very long events. A reasonable strategy for runners and cyclists is to use it through strength and injury-prevention blocks, then stop two to four weeks before a goal race to shed the water. That is reasoning rather than trial evidence, so treat it as a sensible experiment.
Brain and mood Promising
The brain uses about a fifth of the body's resting energy and, like muscle, stores phosphocreatine. Supplementation raises brain creatine modestly, and trials have found improvements in memory and reasoning, particularly when the brain is under stress: after sleep deprivation, during demanding mental work, and in older adults. There is also adjunct data in depression and pilot work in dementia. Because muscle takes most of a small dose for itself, the doses involved are higher than for muscle. This is now a large enough subject that it has its own page: creatine and the brain.
Questions
Not directly. Pooled analyses show a small reduction in fat mass with creatine plus training, most likely because more lean tissue burns more energy. It will not stop weight loss on a diet, but the water gain can hide fat loss on the scales for a few weeks.
Less than strength athletes. It has little effect on steady-state endurance and adds a little mass. It helps surges, intervals and sprint finishes, and may reduce inflammation after very long events. Some endurance athletes use it in training blocks and stop a few weeks before racing.
At 8 to 12 g a day alongside resistance training, a two-year trial slowed hip bone loss in postmenopausal women. It did not increase density, and there is no bone benefit without exercise. It is not a treatment for osteoporosis.
Probably, though some researchers suggest 7 to 8 g for older adults because lower-body stores tend to be more depleted. The bigger lever is resistance training; creatine without it does little for ageing muscle.