Is Creatine Safe? Yes — And the Blood Test Explains the Panic

Yes, in healthy people at ordinary doses [1].

Our main source is the International Society of Sports Nutrition’s position stand — the society’s official position, set out as a review of the research — and it quotes bigger numbers: up to 30 grams a day, for five years. But when it names the studies behind those numbers, the people in them are patients: children and adults with neurodegenerative diseases or inherited creatine-deficiency disorders, given creatine as treatment [1].

The record in healthy people is shorter. College football players took 5 to 10 grams a day for up to 21 months, and athletes who had been taking up to 10 grams a day for between ten months and five years were compared with a group who had not. Neither turned up harm to the kidneys [1]. Beyond a year, a 2025 review of the kidney research calls the data sparse [2].

And know who asked for that position stand: the Council for Responsible Nutrition, the supplement industry’s leading trade association, alongside the society itself. The Council also paid for its preparation, and seven of its ten authors declare industry ties, including research grants from and advisory work for companies that sell creatine [1]. That does not make it wrong. It is why the independent evidence further down this page matters.

But the interesting part isn’t the safety data. It’s that we know exactly why everyone got scared, and it’s a genuinely good mistake.

Your blood test measures the wrong thing

When a doctor checks your kidneys with a standard blood panel, the number they look at is serum creatinine.

Creatinine is what creatine turns into when your body is finished with it. It is the ash. Your muscles burn through creatine, the leftovers wash into your blood, your kidneys filter them out, and the amount sitting in your blood at any moment is a decent proxy for how well that filtering is going.

Decent proxy. Not the thing itself.

So what happens when you deliberately put more creatine into your muscles? More ash. More creatinine in the blood. The number goes up.

If the extra creatine is why the number rose, nothing has gone wrong with your kidneys. You have loaded more raw material into the front of a process and more of the by-product came out of the back. But the number on the page is the number labelled kidney function, and it went the wrong way, and that is a genuinely alarming thing to be told.

So somebody measured the organ instead of the gauge

A 2025 meta-analysis in BMC Nephrology pulled together 21 studies on exactly this question and pooled the blood-test results of 177 people taking creatine against comparison groups who were not [2].

Serum creatinine went up. Small, but real.

And glomerular filtration rate showed no change the analysis could detect [2].

That second number is the one that matters. Glomerular filtration rate — GFR — is how fast your kidneys are cleaning your blood: the organ doing its job, rather than a by-product floating in it. The authors’ conclusion is that what you’re seeing is metabolic turnover, not kidney damage [2].

The gauge moved. The engine didn’t.

How solid is that engine result? Thinner than that line makes it sound. The filtration finding pools just five small studies, fewer than 150 people in all, and the authors describe it as mixing filtration that was measured directly with filtration that was estimated [2]. The usual estimate is worked out from creatinine, the very number creatine pushes up, and the authors themselves warn that creatinine-based estimates can mislead in creatine studies [2].

So look at a trial that measured the organ directly. In São Paulo, young men who had lifted weights for years and ate a high-protein diet took creatine (20 grams a day for five days, then 5 grams a day) or a dummy powder, a placebo, for 12 weeks; 26 finished. Their filtration was measured with a tracer — a marker injected into a vein, whose clearance from the blood shows how fast the kidneys filter — which the researchers used because creatine’s conversion to creatinine can make the usual tests falsely suggest the kidneys are slowing. The creatine group’s filtration came out no different from the placebo group’s [5].

It is one small trial, and its authors say twelve weeks is too short for a definitive answer; it was designed to run a year, until too many volunteers dropped out [5]. But it measured the engine rather than the gauge, and on the engine, creatine made no difference.

Worth noting who paid for these two. The 2025 analysis declares no funding and no competing interests [2]. The São Paulo trial was funded by two Brazilian public research agencies, and its authors declare no conflict of interest [5]. Neither was paid for by the supplement industry, and both reached the same kidney answer as the industry-funded position stand.

Where the fear actually started

April 1998. The Lancet publishes a letter titled “Renal dysfunction accompanying oral creatine supplements” [3].

A letter. Describing one patient.

Here is the part that got lost on the way out of the building: it was argued with, in print, almost immediately. The Lancet published two replies on 18 July that same year [3]. Three months from case report to published disagreement, which is roughly the speed of light in academic publishing.

The news ran with the scare instead.

By 2000, two Belgian researchers — the pair behind one of those July replies [3] — had written an entire review with the subtitle “fact or fiction?”, saying outright that they were writing it to set the science against news coverage that “do[es] not hesitate to draw broad conclusions from individual case reports” [4].

Their own evidence came from small groups of athletes, checked with clearance tests (how fast the kidneys clear a substance from the blood) and urine protein: after five days of creatine, after nine weeks, and in athletes who had taken it for up to five years. They found no adverse effects on kidney function [4]. They were also plain that well-controlled studies of creatine’s side effects were “almost nonexistent” [4]. Most of those came later, and they are what the section above is built on.

That was twenty-six years ago, and the worry never left. The 2025 kidney review says concern about creatine and the kidneys persists, largely because of that raised creatinine number [2].

Who this doesn’t cover

The safety finding is for healthy people, and that word is doing real work.

If you already have kidney disease, or you are on medication that affects kidney function, none of the above is about you, and the person to ask is a clinician who can see your actual numbers. This site reads research and reports what it found. It is journalism, not medical advice, and it does not know your history.

One practical thing worth carrying, though: if you take creatine and you are booked in for a blood test, say so. A slightly elevated creatinine reading in someone who supplements has a boring explanation, and your doctor can only rule it in if they know to.

The one-line version

Creatine raises the number people use to check your kidneys, without changing what your kidneys are doing.

A 1998 letter about one patient became a lasting piece of gym folklore. Two of the researchers who answered it in print went on to find no kidney harm in the athletes they tested, and the controlled trials that came later found the same. If you want the other half of the creatine story — the weight that shows up on the scale in week one, and why it isn’t fat — that has its own verdict.