What Does Creatine Actually Do?

Key takeaways

• Creatine’s mechanism is ATP regeneration during efforts lasting roughly 1–10 seconds.
• Typical strength gains in meta-analyses are 5–15% above training alone, not dramatic.
• It works for men and women identically — the mechanism is not sex-specific.
• 3–5g daily is the effective dose. Loading is optional and only changes how fast you saturate.
• It is among the most-studied supplements in existence, with a strong long-term safety record.

What does taking creatine do to your body?

Creatine is stored in skeletal muscle as phosphocreatine. During brief maximal effort — a heavy set,
a sprint, a jump — your muscles use ATP faster than aerobic metabolism can replace it. Phosphocreatine
donates a phosphate group to ADP, regenerating ATP almost immediately.

Supplementing raises muscle phosphocreatine stores by roughly 20–40% in people who start with
below-saturation levels. More stored phosphocreatine means the ATP regeneration pathway runs longer
before fatigue forces you to stop. That is the entire mechanism, and everything else follows from it.

A secondary effect is cell volumisation: creatine draws water into muscle cells, which accounts for
the rapid 1–2kg scale increase most people see in the first fortnight. That is intramuscular water,
not fat and not yet muscle.

What does the NHS say about creatine?

The NHS does not prescribe creatine for athletic performance, and UK public health guidance treats it
as a food supplement rather than a medicine. That is consistent with its regulatory status: creatine
monohydrate is legally sold as a supplement across the UK and EU, and the European Food Safety Authority
has accepted the claim that creatine increases physical performance in successive bouts of short-term,
high-intensity exercise.

It is worth being clear about what that status means. Creatine is not a licensed medicine, so nobody
is making therapeutic claims for it. It is also not a controlled substance, and it is permitted under
WADA rules — unlike most other categories discussed on this site.

Why do doctors say not to take creatine?

Most do not. The caution that circulates usually traces to two things: kidney concern, and drug
interaction caution in people with existing renal impairment.

On kidneys, the concern is largely a measurement artefact. Creatine supplementation raises serum
creatinine — a breakdown product used as a kidney function marker — without impairing actual kidney
function. A clinician reading an elevated creatinine without knowing about supplementation may
reasonably investigate further. Tell whoever orders your bloods that you take creatine, and that
confusion disappears.

In people with pre-existing kidney disease, the caution is genuine and supplementation should be a
medical decision. In healthy adults, controlled trials running up to five years have not demonstrated
renal harm.

What foods are high in creatine?

Red meat and fish are the main dietary sources. Beef contains roughly 2g per kilogram raw; herring
is higher, salmon and tuna somewhat lower. Cooking degrades some of it.

The practical consequence is that vegetarians and vegans start with meaningfully lower muscle
creatine stores and tend to show the largest response to supplementation. Omnivores eating substantial
red meat are partially saturated already and respond less dramatically.

What the research actually shows

The evidence base here is unusually deep. Kreider et al. (2017), the International Society of Sports
Nutrition position stand, reviewed hundreds of studies and concluded creatine monohydrate is the most
effective ergogenic nutritional supplement available for increasing high-intensity exercise capacity
and lean mass during training.

Effect sizes are consistent but modest. Meta-analyses generally find strength improvements in the
5–15% range above training alone, with the largest effects in movements dominated by the
phosphocreatine system. Endurance performance shows little to no benefit, which is exactly what the
mechanism predicts.

Cognitive research is a newer and more tentative area — some trials show benefit under sleep
deprivation or in vegetarians, with less consistent findings in rested omnivores.

Practical summary

Take 3–5g of creatine monohydrate daily, at whatever time suits you, indefinitely. Monohydrate is
the form with the evidence; the more expensive salts and esters have not demonstrated superiority over
it in head-to-head work.

Expect a small scale increase from water in the first two weeks, then gradual strength progression
over one to three months. If you buy creatine powder rather than capsules you will pay considerably
less per gram for exactly the same compound. Adequate protein intake matters more than any supplement,
so a sensible protein powder habit belongs alongside it rather than after it.

Frequently asked questions

Do I need to cycle creatine?

No. There is no evidence that continuous use downregulates the transporter in a way that requires
breaks. Muscle stores simply return to baseline over four to six weeks if you stop.

Does creatine work for women?

Yes, through the identical mechanism. Some research suggests women may start with slightly lower
baseline stores, which would if anything predict a marginally larger response.

Is creatine a steroid?

No. Creatine is an amino acid derivative that affects cellular energy metabolism. It has no hormonal
activity and does not interact with androgen receptors.

Should I take creatine on rest days?

Yes. The goal is keeping muscle stores saturated, which depends on daily intake rather than training
timing.