Does Creatine Cause Cancer?
This week my client Jenn asked me a great question:
"I would love to learn more about creatine. The details seem very mixed, and lots of people claim it causes cancer to spread faster. What's the truth?"
This evoked a visceral response in me, because I love creatine and I hate cancer.
I remembered reading about some mouse studies years ago linking creatine to cancer spread, but I couldn't recall the mechanism or why I'd been so quick not to worry. So I took a deep dive. Here's what you need to know.
Where The Fear Comes From
Aggressive cancer cells are energy-hungry, and several independent labs have found they can hijack the creatine energy system, the same one your muscles run on, to fuel their own growth and spread.
It shows up in pancreatic cancer, where the creatine system helps tumor cells invade and reach the liver (1). It shows up as a weak spot in certain leukemias, and in kidney and colorectal cancers too (2).
And the big one some people quote when making these claims: a 2021 study found that oral creatine sped up cancer spread in mice by flipping on a cellular switch called Smad 2/3 (3).
Quick translation: think of Smad 2 and 3 as little messengers inside a cell. When something flips them on, they sprint to the cell's control center with a note that says "pack up and move out." Creatine helped flip that switch in those cancer cells.
Terrifying. Chuck the creatine out the window and never look back, right? Not so fast.
Humans Are Not Mice (And No One Takes 100g Of Creatine/Day)
That same study found that while creatine made the cancer spread faster, it shrank some of the original tumors.
Not only that, a group of the field's leading creatine researchers later published a formal critique of it, pointing out that the mice were severely immunocompromised and that no other lab has reproduced the finding (4).
Not only that (yes, two "not only thats"!), the dose was enormous. Like, a metric butt ton. The critics ran the numbers, and the creatine those mice got was equivalent to a 70 kg person eating 50 to 100 grams a day, or more, for a prolonged period. Normal human supplementation is 3 to 10 grams a day. These were not realistic doses.
Now flip to the side where the evidence actually involves humans and supplements.
Is Creatine Safe?
That scary mechanism cuts both ways. Creatine is also a key fuel source for the CD8 "killer" T cells your immune system uses to hunt cancer down, and it even boosts the effect of certain immunotherapy drugs in mice (5).
When researchers looked at human data from a survey of nearly twenty-six thousand adults, higher creatine intake lined up with slightly lower cancer rates (6). Correlation isn't causation, of course, and people who eat more creatine likely have other healthy habits muddying the picture. But here's the kicker: if creatine truly fed cancer in humans, you'd expect to see a positive correlation between cancer and creatine, not the opposite.
Last, a December 2025 expert review went through every lingering safety fear and concluded there is no evidence creatine causes cancer in people (7).
In other words, creatine is absolutely safe and does not increase risk of cancer.
You want to know what grinds my gears?
Creatine is one of the most well researched, low risk, high reward supplements out there. 99% of people would benefit from taking it for more strength and power in the gym, faster muscle growth, better recovery between sessions, sharper thinking (especially when you're underslept), and maintaining muscle and bone as you age. And there are probably thousands of people, if not more, who avoid it because of bogus TikTok claims that go viral precisely because they're scary.
Keep taking your creatine, let me know if you have any questions, and delete TikTok off your phone.
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If you want to learn more about creatine or Michael Jordan, check out my past articles:
I've Taken Creatine Since 2009. Here's Why.
Creatine - The Michael Jordan Of Supplements
**Of course, none of this is medical advice, just my read on the research. If you have cancer or have had it in the past, talk to your oncologist before adding any supplement, creatine included.
Sources:
https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2024.1460057/full
https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1682746/full
Best,
John
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