Supplements

Creatine: what the evidence actually shows.

By Luigi · 7 min read

I don't sell supplements, and I'm not about to start. But clients ask me about creatine more than anything else, so it's worth doing properly: not the forum scare stories about kidneys, not the Instagram claims it'll change your physique overnight. Just what the actual research says — and it says more, with better evidence, than almost anything else sold in a tub.

That's worth sitting with for a second, because the supplement industry runs on hype and creatine is the opposite case: it's one of the most-studied compounds in sports nutrition, with decades of trials and multiple meta-analyses behind it. So when I tell you to be sceptical of supplements generally, creatine is the exception I make — and below is why, including the parts where the evidence is genuinely thinner than people assume.

What it actually does

Creatine tops up phosphocreatine stores in muscle, which your body uses to regenerate ATP — the fuel for short, hard efforts. More phosphocreatine on hand means you can produce near-maximal force for a few more reps or a few more seconds before you run out of gas. That's the entire mechanism. It's not anabolic, it's not a hormone, and it won't do anything for a 10k run. It helps with the stuff that depends on brief, maximal output: lifting, sprinting, repeated efforts with short rest.

The strength evidence

Two linked meta-analyses pooled decades of trials on exactly this. For lower-body lifts, creatine improved squat and leg press performance with small-to-moderate effect sizes (around 0.3), consistent across age, sex, training status and dosing protocol^[1]. For upper-body lifts, the same team found a similar pattern — bench press effect size around 0.27, chest press exercises around 0.68, with the overall upper-limb effect landing around 0.3 as well^[2]. In plain terms: a real, repeatable, statistically solid effect — but a small-to-moderate one, not a transformation. It's the difference between finishing a set and grinding out one more rep, not the difference between two different people.

The kidney myth

This is the one that actually stops people taking something with good evidence behind it. The International Society of Sports Nutrition's position stand — reviewing decades of research — concludes creatine monohydrate is one of the most effective and safest supplements available, with no credible evidence of kidney or liver harm in healthy people at standard doses^[3]. A dedicated long-term study put this to the test directly: athletes on creatine for up to 21 months showed no meaningful differences across a 69-marker panel of blood and urine health markers compared to athletes who weren't supplementing^[4]. The myth likely comes from creatine raising serum creatinine slightly — creatinine is a kidney-function marker, but in this case the rise reflects creatine turnover, not kidney strain. If you already have kidney disease, that's a conversation for your doctor, not for me. For everyone else, this is one of the better-supported safety profiles of anything in a supplement aisle.

Who actually benefits most

Not everyone starts from the same baseline. People who eat little or no meat and fish — the main dietary sources of creatine — tend to start with lower muscle creatine stores, so supplementing tends to move the needle further for them^[3]. Older adults are the other group worth flagging: a 2021 review highlighted creatine's role in supporting muscle mass and function alongside resistance training in ageing populations, which matters given how much strength training alone already does for that group^[5] — see my piece on muscle loss after 50 for why that's worth taking seriously on its own.

Where I'll be honest the evidence is thin

You'll see claims about creatine improving brain function, mood, even recovery from concussion. The most-cited study here is one small, 45-person trial from 2003 that found improved working memory and processing speed under creatine supplementation^[6]. That's one study, over two decades old, with a small sample — interesting, not proven. If someone tells you creatine is a confirmed cognitive enhancer, they're overselling a single result. I'd file this under "promising, not settled" rather than something to train or dose around.

Water retention is real but usually misunderstood — the small weight gain some people see (often 1–2kg early on) is water pulled into the muscle cell itself, not bloating under the skin. It's also not universal; plenty of people notice nothing on the scale at all.

What I actually tell clients

• 3–5g a day, every day. The "loading phase" (20g/day for a week) saturates muscle faster, but a flat daily dose gets you to the same place within about a month. Skip the drama, take the smaller dose.
• Timing doesn't matter much. Take it with food, any time of day, consistently. The evidence doesn't support a magic pre- or post-workout window for this one.
• It's not a substitute for training or food. It makes your hard sets marginally harder to fail, nothing more. If your programme or your plate isn't sorted, creatine won't rescue either.
• Plain creatine monohydrate. It's the form almost all of this research is actually on. The "advanced" buffered or liquid versions are marketed on claims the evidence above doesn't support.