On 12 December 2025, the US Food and Drug Administration sent a warning letter to an online seller of products marketed as SARMs, telling it that products sold as “Ostarine MK-2866”, “MK-677 Ibutamoren”, “Cardarine GW501516” and “LGD-4033 Ligandrol” are unapproved new drugs under section 505(a) of the Federal Food, Drug, and Cosmetic Act. Selling them across state lines, the FDA wrote, violates federal law. The letter was issued by the FDA’s Center for Drug Evaluation and Research after a review of the seller’s website in November 2025.
What the FDA said
- “Research use only” does not help. The products carried “for research use only” statements, but the FDA said evidence from the labeling and website, including claims about muscle growth, fat loss and recovery, showed they were intended as drugs for human use.
- They are “new drugs”. Because they are not generally recognized as safe and effective for the uses described, they need an approved application, and none exists.
- Safety concerns. The FDA repeated that life-threatening reactions, including liver toxicity, have occurred in people taking SARM products, and that SARMs may increase the risk of heart attack and stroke.
- Next steps. The seller was asked to respond within 15 working days; the FDA said failure to fix the violations may lead to regulatory or legal action, including seizure and injunction.
Why it matters
The letter covers four of the most popular compounds on this site, two of which are not SARMs: MK-677 is a growth hormone secretagogue and cardarine a PPAR-delta agonist. It confirms the FDA’s long-standing position, set out on its consumer page about bodybuilding products, that SARM products are not dietary supplements but unapproved drugs, and that the “research chemical” label used across the industry does not change their legal status. The FDA’s consumer page lists the risks it associates with SARM products, including liver injury and acute liver failure, heart attack or stroke, psychosis, infertility and testicular shrinkage.
What the evidence says about these four compounds
| Compound | Status | Key safety findings |
|---|---|---|
| Ostarine | Phase 3; not approved | Lower testosterone and HDL; liver injury case reports |
| LGD-4033 | Phase 2; not approved | Suppression at 1 mg/day; biopsy-confirmed liver injury cases |
| MK-677 | Phase 3; not approved; FDA Category 2 for compounding | Higher blood sugar; heart-failure signal in frail older adults |
| Cardarine | Development stopped in 2006 | Cancers in 2-year rat and mouse studies |
For the rules outside the US, see are SARMs legal? All four are banned in sport at all times; see SARMs and WADA.
Frequently asked questions
Are SARMs illegal in the US?
Illegal to sell for human useEvidence: Law
The FDA says products containing SARMs are unapproved drugs, not dietary supplements, and that selling them for human use violates the FD&C Act. Its December 2025 warning letter applied this to ostarine, MK-677, cardarine and LGD-4033 products.
Does a "research use only" label make SARMs legal?
No, according to the FDAEvidence: Law
In the December 2025 letter, the FDA said the website and labeling showed the products were intended for human use, despite "research use only" statements.
Which products did the FDA name?
Ostarine, MK-677, cardarine, LGD-4033Evidence: Law
Products sold as "Ostarine MK-2866", "MK-677 Ibutamoren", "Cardarine GW501516" and "LGD-4033 Ligandrol", among others.
What risks does the FDA link to SARMs?
Liver toxicity, heart attack, strokeEvidence: Law
The letter cites life-threatening reactions including liver toxicity, and a possible higher risk of heart attack and stroke. The FDA's consumer page also lists psychosis, infertility and testicular shrinkage.
Sources
- FDA Warning Letter to an online seller of products marketed as SARMs (MARCS-CMS 719257), 12 December 2025
- FDA: Certain bodybuilding products put consumers at risk for heart attack, stroke, serious liver damage and more (content current as of 2 December 2025)
- The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial
- The safety, pharmacokinetics, and effects of LGD-4033, a novel nonsteroidal oral, selective androgen receptor modulator, in healthy young men
- FDA Briefing Document, Pharmacy Compounding Advisory Committee, 29 October 2024: Ibutamoren Mesylate
- Rat carcinogenicity study with GW501516, a PPAR delta agonist (Geiger et al., The Toxicologist 2009, abstract 895)