Short answer: no human study has shown that SARMs cause cancer, but none has been long enough to rule it out. The longest SARM trials lasted a few months. Two SARMs, enobosarm (ostarine) and RAD-140, are actually being tested as treatments for a type of breast cancer. The compound with a real cancer signal is cardarine (GW501516), which is often sold alongside SARMs but is not one: its developer stopped work on it after long-term animal studies found cancers in many organs.
What the research says, compound by compound
| Compound | What is known about cancer | Evidence |
|---|---|---|
| Ostarine (enobosarm) | Tested as a treatment. In women with advanced AR+/ER+/HER2- breast cancer, 32% (9 mg/day) and 29% (18 mg/day) had clinical benefit at 24 weeks. Also tested for muscle wasting in cancer patients. | Trial |
| RAD-140 | Tested as a treatment. In a Phase 1 trial in 22 women with advanced breast cancer, 1 had a partial response; liver-enzyme rises were common. In mice with human breast tumor grafts, it slowed tumor growth. | Trial; animal |
| LGD-4033 | No cancer data. Its trials lasted 3 to 12 weeks; PSA did not change in the 21-day trial in young men. | Trial (short) |
| Cardarine (not a SARM) | In GSK’s 2-year studies, rats and mice developed drug-related tumors in many organs, some at every dose. In polyp-prone mice it made intestinal polyps larger and more numerous. Development stopped in 2006. | Animal; regulator warning |
| MK-677 (not a SARM) | No trial has shown it causes cancer. It raises GH and IGF-1; the FDA notes that drugs raising them carry tumor warnings and that long-term safety data are lacking. | Not established |
All figures come from the compound records in our SARMs database, where every number links to its study.
SARMs as cancer treatments
There is no research showing that SARMs cause cancer. Some research is testing whether they can help treat it.
In the past, scientists tried using steroids to treat breast cancer, but they had too many side effects. So, they started looking into other drugs like SARMs to see if they could work better.
In mice carrying human breast tumors that are positive for both the androgen and estrogen receptor, RAD-140 slowed tumor growth (animal data). In people, enobosarm (ostarine) gave clinical benefit at 24 weeks to about 3 in 10 women with this type of advanced breast cancer, and RAD-140 gave a partial response in 1 of 22 women in its first trial.
Enobosarm was also tested for cachexia, the muscle wasting seen in cancer. In a Phase 2 trial, cancer patients gained a median 1.0–1.5 kg of lean mass. Two later Phase 3 trials in lung cancer missed their main goals.
Being tested as a cancer drug is not the same as being proven safe for healthy people. These trials ran for months, in patients with advanced disease, under medical supervision.
No SARM is approved anywhere we could find, and they have other side effects: lower testosterone and HDL cholesterol, and case reports of serious liver injury.
Why people worry: the two common theories
Theory 1: constant androgen-receptor activation
The theory goes as follows: If you keep your androgen receptors activated all of the time, the chance for a mutation to occur during gene expression heightens which could lead to cancer.
What we know: testosterone and other androgens act on the same receptor, and prostate growth is the main cancer-related concern with them. SARMs were designed to act more on muscle and bone than on the prostate, and PSA did not change in the 21-day LGD-4033 trial. But short trials cannot show what years of use do, so the honest answer is not established.
Theory 2: anything that grows tissue might grow tumors
This theory could be summed up as: Cancer is basically the unregulated growth of cells and taking drugs that accelerate cell growth can lead to an increase in cancer risk because of potential mutations.
This concern is more relevant to compounds that raise growth factors, such as MK-677 (GH and IGF-1) and IGF-1 LR3, than to SARMs. For MK-677 the FDA notes that drugs raising GH and IGF-1 carry warnings about tumors, and that long-term safety data are lacking. A few cancers were reported in MK-677 trial participants, without any judgment that the drug caused them.
What about cardarine?
Cardarine (GW501516) is not a SARM; it is a PPAR-delta agonist. It is the one compound in this group with a clear cancer signal. In GlaxoSmithKline’s 2-year rat study, drug-related tumors appeared in many tissues at every dose tested, including liver, bladder, thyroid, stomach and uterus; in the 2-year mouse study, liver and stomach cancers appeared. In mice prone to intestinal polyps, it made polyps bigger and more numerous. GSK stopped development in 2006, and WADA took the rare step of warning athletes directly in 2013. Read more in our cardarine fact sheet.
MK-677, IGF-1 and cancer
MK-677 raises growth hormone and IGF-1. That is why caution is usually advised for anyone with a current or past cancer, and why the FDA lists missing long-term safety data among its concerns. No trial has shown that MK-677 causes cancer. See the MK-677 side effects page for the full trial data.
The risks you can actually check
The bigger near-term risks with SARMs are not cancer but liver injury, lower testosterone and lower HDL cholesterol, all seen in trials or case reports. Product quality is a risk too: in a 2017 test of 44 products sold online as SARMs, only 52% contained a SARM and 39% contained another unapproved drug. Our bloodwork guide lists the markers that studies tracked, and the lab tests guide explains how to read a certificate of analysis.
Final thoughts
There is no evidence that SARMs cause cancer, and some are being tested as cancer treatments. There is also no long-term human safety data, so the risk is unknown rather than zero. Cardarine is the exception with a real cancer signal from animal studies, and MK-677 carries the general caution that applies to anything raising GH and IGF-1.
Related: SARMs side effects · do SARMs cause acne? · SARMs and blood pressure
Frequently asked questions
Do SARMs cause cancer?
Not shown; long-term risk unknownEvidence: Limited
No human study has shown that they do, but the longest SARM trials lasted months, not years, so long-term risk is not established. Enobosarm (ostarine) and RAD-140 are being tested as breast cancer treatments.
Can SARMs cause prostate cancer?
Not shownEvidence: Trial
SARMs were designed to act less on the prostate than testosterone does, and PSA did not change in a 21-day LGD-4033 trial. No long-term study has looked at prostate cancer risk.
Can SARMs cause breast cancer?
No evidence that they doEvidence: Trial
Enobosarm (ostarine) and RAD-140 have been tested as treatments for androgen-receptor-positive breast cancer, with clinical benefit in about 3 in 10 women on enobosarm.
Can SARMs be used as a cancer treatment?
Being studied, not approvedEvidence: Trial
Enobosarm was tested for muscle wasting in cancer (two Phase 3 lung cancer trials missed their main goals) and for AR+/ER+ breast cancer. RAD-140 (now vosilasarm) is in a Phase 1/2 breast cancer trial.
Does LGD-4033 cause cancer?
No link found; trials were shortEvidence: Limited
No study has linked LGD-4033 to cancer, but its trials lasted only 3 to 12 weeks. Its known side effects are lower testosterone and HDL cholesterol, and case reports of liver injury.
Does cardarine cause cancer?
Yes, in animal studiesEvidence: Animal
In GSK's 2-year studies, rats and mice developed tumors in many organs, some at every dose, and development was stopped in 2006. There are no human data, because long-term human studies were never done.
Does MK-677 cause cancer?
Not shown; long-term data lackingEvidence: Limited
No trial has shown that it does. It raises GH and IGF-1, and the FDA notes that drugs doing this carry tumor warnings and that long-term safety data for MK-677 are lacking.
Sources
- Activity and safety of enobosarm, a novel, oral, selective androgen receptor modulator, in androgen receptor-positive, oestrogen receptor-positive, and HER2-negative advanced breast cancer (Study G200802): a randomised, open-label, multicentre, multinational, parallel design, phase 2 trial
- A First-in-Human Phase 1 Study of a Novel Selective Androgen Receptor Modulator (SARM), RAD140, in ER+/HER2- Metastatic Breast Cancer
- Selective Androgen Receptor Modulator RAD140 Inhibits the Growth of Androgen/Estrogen Receptor-Positive Breast Cancer Models with a Distinct Mechanism of Action
- Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial
- The safety, pharmacokinetics, and effects of LGD-4033, a novel nonsteroidal oral, selective androgen receptor modulator, in healthy young men
- Rat carcinogenicity study with GW501516, a PPAR delta agonist (Geiger et al., The Toxicologist 2009, abstract 895)
- Mouse carcinogenicity study with GW501516, a PPAR delta agonist (Newsholme et al., The Toxicologist 2009)
- Activation of nuclear hormone receptor peroxisome proliferator-activated receptor-delta accelerates intestinal adenoma growth
- WADA issues alert on GW501516 (21 March 2013)
- FDA Briefing Document, Pharmacy Compounding Advisory Committee, 29 October 2024: Ibutamoren Mesylate
- Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet