There is no direct evidence that SARMs cause cancer in humans, but there is also no evidence proving they don’t. No SARM has been approved by the FDA for any use, and no long-term human safety studies exist. The honest answer is that the cancer risk of SARMs is unknown, with some genuinely concerning signals from animal research and a complete absence of the kind of data that would rule the risk out.
What SARMs Actually Do in Your Body
SARMs, or selective androgen receptor modulators, are synthetic compounds that bind to the same receptors as testosterone. Once inside a cell, a SARM locks onto the androgen receptor and travels to the nucleus, where it influences which genes get turned on or off. The “selective” part is the selling point: in theory, SARMs activate muscle-building pathways without triggering the same effects in the prostate, skin, or other tissues where androgens cause problems.
That selectivity comes from how different tissues respond to the drug. Each tissue has its own mix of helper proteins (called cofactors) that shape what happens after the SARM binds to the receptor. In muscle, the result may be growth. In prostate tissue, some SARMs appear to do the opposite, actually suppressing cell proliferation. But this tissue-specific behavior is still poorly understood, and the full range of effects on cell growth throughout the body has not been mapped out in humans.
The Cardarine Problem
Much of the cancer fear around SARMs traces back to a compound called GW501516, better known as Cardarine. Cardarine is technically not a SARM. It works through a completely different receptor (a fat-metabolism pathway rather than the androgen receptor), but it’s sold alongside SARMs and marketed to the same audience. The distinction matters because Cardarine’s cancer data is often incorrectly applied to all SARMs.
In preclinical studies run by GlaxoSmithKline, rats and mice given Cardarine for 104 weeks developed tumors in multiple organs. GSK abandoned the drug’s development because of these findings. The doses used were higher than what humans typically take, and two years represents most of a rodent’s lifespan, but the results were alarming enough to kill a major pharmaceutical program. No equivalent tumor data exists for actual SARMs like Ostarine, LGD-4033, or RAD140, but no one has run those same 104-week studies either.
What Clinical Trials Have Shown
The SARM with the most human data is enobosarm (also called Ostarine or MK-2866). It has been tested in phase 2 clinical trials for conditions like muscle wasting in cancer patients and for androgen receptor-positive breast cancer. In a breast cancer trial published in The Lancet Oncology, patients receiving enobosarm at two different doses tolerated the drug reasonably well. The most common serious side effects were temporary spikes in liver enzymes, elevated calcium levels, and fatigue. The researchers concluded the drug was “safe and well tolerated with no concerning adverse effects or serious clinical outcomes.”
That sounds reassuring, but context is everything. Clinical trials last months, not years. Cancer can take a decade or more to develop from an initial trigger. These trials tell us that enobosarm doesn’t cause rapid, obvious tumor growth. They tell us almost nothing about whether years of use could promote cancer through slower mechanisms like chronic liver stress or sustained androgen receptor activation in tissues that weren’t being monitored.
The Liver Connection
One indirect pathway worth understanding is liver damage. SARMs are consistently linked to liver injury, ranging from mild enzyme elevations to acute liver failure. The FDA specifically lists liver injury among the serious health problems associated with SARM use. Traditional anabolic steroids, which work through the same androgen receptor, are known to cause a spectrum of liver problems, and long-term steroid use has been linked to the development of liver tumors.
Whether SARMs carry the same long-term liver tumor risk is genuinely unknown. The mechanism is plausible: repeated chemical stress to liver cells forces them to regenerate more frequently, and each round of cell division is an opportunity for DNA errors that can eventually become cancerous. But plausible is not the same as proven, and no case reports have directly linked SARM use to liver cancer in humans.
Some SARMs Are Being Studied to Fight Cancer
Here’s where the picture gets more complicated. Several SARMs are actively being researched as potential cancer treatments. RAD140 (Testolone), one of the most popular SARMs in the bodybuilding community, has been shown to inhibit the growth of certain breast cancer cells in laboratory and animal models. It appears to work by activating the androgen receptor in breast tissue in a way that suppresses estrogen receptor signaling, effectively starving estrogen-dependent tumors.
Another SARM called S42 has shown the ability to suppress prostate cancer cell growth by blocking key proliferation signals, including a growth pathway called ERK-MAPK. It also reduced markers of tumor activity like PSA and Ki67 in preclinical studies. A different compound, MK-4541, went a step further and actually triggered cancer cell death in androgen-independent prostate cancer cell lines.
These findings don’t mean SARMs prevent cancer. They mean that in specific cancer types, in laboratory conditions, certain SARMs interfere with tumor growth. The same compound that suppresses cancer in one tissue could theoretically promote it in another, because the androgen receptor behaves differently depending on where it sits in the body. A drug that blocks proliferation in the prostate might do something entirely different in the liver or colon.
The Real Risk: No One Knows What You’re Taking
Every SARM sold online or in supplement stores is an unapproved drug product. The FDA has issued multiple warning letters to companies selling SARMs and has pursued criminal actions against distributors. Independent testing of products marketed as SARMs has repeatedly found that they contain incorrect doses, different compounds than what’s listed on the label, or additional unlisted substances altogether.
This means that even if a specific SARM like enobosarm has a relatively clean safety profile in clinical trials, the product you buy online may contain something else entirely. It could be a different SARM, a prohormone, or Cardarine, the compound that actually did cause tumors in animal studies. The cancer risk of a mislabeled or contaminated product is impossible to estimate because you don’t know what you’re being exposed to.
Why the Question Can’t Be Fully Answered Yet
Proving that a substance causes cancer in humans requires either large epidemiological studies tracking users over many years, or such strong and consistent animal data that the risk is considered near-certain. SARMs have neither. The longest human trials have lasted months. No one has followed a cohort of recreational SARM users for five or ten years to see what happens. The animal studies that do exist are limited, and the most alarming cancer data comes from Cardarine, which isn’t technically a SARM.
What exists instead is a collection of warning signs: liver toxicity that mirrors early patterns seen with anabolic steroids, activation of a receptor system deeply involved in cell growth, an unregulated market full of mislabeled products, and a complete absence of the long-term safety data that would be required for any approved medication. The FDA’s position, as of 2023, is that SARMs are “potentially dangerous” and have “not been reviewed for safety or efficacy.” Cancer is not specifically listed among their warnings, but the agency’s concern centers on the fact that these are unstudied drugs being used without medical oversight.
The bottom line is that no one can tell you SARMs are safe from a cancer standpoint, because the studies that would answer that question have never been done.