Classification explainer

Is ostarine a steroid? MK-2866 classification and legal status

By the Decadewise team Education only Last reviewed 27 July 2026 No dosing table on this page

Short answer

The classification: ostarine, also called enobosarm or MK-2866, is a nonsteroidal selective androgen receptor modulator. It binds the androgen receptor, which is the same receptor testosterone binds, but it is not built on a steroid backbone.

The legal definition: federal law defines an anabolic steroid as a drug or hormonal substance chemically and pharmacologically related to testosterone. Ostarine is not, and it is not on the schedule.

What it is instead: an unapproved new drug, in FDA's stated position. The agency has said so in warning letters, which set out its view that the products fall outside the dietary supplement definition because the article entered substantial public clinical investigation first.

In sport: the 2026 WADA Prohibited List names enobosarm at S1.2, other anabolic agents, prohibited at all times.

The practical catch: when products sold as SARMs were bought and analysed, roughly half held no SARM at all.

On this page

Short answer What a steroid is in law What ostarine is The trial record Is ostarine a steroid? Is it legal in the US? Did the SARMs Control Act pass? Is it banned in sport? What is in the bottle? What is unsettled The safety picture How this is sourced Related pages The disclaimer

What counts as a steroid in law

The statutory text: the Controlled Substances Act defines an anabolic steroid as "any drug or hormonal substance, chemically and pharmacologically related to testosterone (other than estrogens, progestins, corticosteroids, and dehydroepiandrosterone)", then lists the compounds it covers.

Two conditions, both required: chemical relation and pharmacological relation. A compound that acts on the androgen receptor but shares no steroid chemistry fails the first test.

Where ostarine lands: outside that definition. It is not a scheduled anabolic steroid under federal law, which is a different statement from saying it is lawful to sell, and the two get conflated constantly.

What ostarine is

The class: the developer described GTx-024, the compound published as enobosarm, as a nonsteroidal selective androgen receptor modulator with tissue-selective anabolic effects in muscle and bone, sparing other androgen-responsive tissue (Dalton, 2011).

The names: ostarine, enobosarm, MK-2866 and GTx-024 all point at the same molecule. Retail listings favour the first and third; the published literature uses the second.

The development history: it went through company-run phase 2 trials in muscle wasting, which is precisely why FDA can exclude it from the supplement definition. Public clinical investigation is the trigger.

The status today: no approved product contains it, in any country's label we could find, and no compendial monograph governs what a bottle has to hold.

The published human record

What the trials measured

How to read this: two company-sponsored randomised trials, each with the amount it administered and the endpoint it reported. The figures belong to those arms and those populations.

Enobosarm in published randomised phase 2 trials

Source	Population	What the trial gave	Reported result
Dalton, 2011	120 healthy men over 60 and postmenopausal women	oral, 12 weeks, dose ranging	dose-dependent rise in total lean body mass, significant at the 3mg arm against placebo; physical function and insulin resistance also improved at that arm
Dobs, 2013	159 in the safety population, patients with cancer and at least 2 percent weight loss; 100 in the evaluable efficacy population	1mg or 3mg once daily by mouth, up to 113 days	in the 100-patient evaluable efficacy population: median lean body mass +1.5kg at 1mg and +1.0kg at 3mg from baseline; placebo change +0.02kg and not significant

Both trials were funded by the developer. Both measured lean mass by dual-energy x-ray absorptiometry.

What the trials were aimed at: muscle wasting, not physique work in healthy young people. The two populations differ: Dalton enrolled healthy men over 60 and postmenopausal women, while Dobs enrolled patients with cancer and recent weight loss. The primary endpoint in both was lean mass.

The reading: a lean-mass signal in a healthy elderly cohort and in a cancer cohort is a real result and a narrow one. It does not carry across to a different population by itself.

Is ostarine a steroid?

No. It is nonsteroidal by chemistry and it sits outside the statutory definition of an anabolic steroid, which requires a drug or hormonal substance chemically and pharmacologically related to testosterone. What it shares with a steroid is the receptor it binds, and that is where the resemblance stops.

Why people assume otherwise: the marketing borrows steroid language, and FDA's own consumer notice describes SARMs as chemical substances that mimic the effects of testosterone and anabolic steroids. Mimicking an effect is not the same as being in the class.

Is ostarine legal in the United States?

Not as a supplement, and not as a drug. In a warning letter dated 23 October 2017, FDA told a seller that products labelled to contain ostarine and LGD-4033 do not meet the definition of a dietary supplement in section 201(ff) of the Federal Food, Drug, and Cosmetic Act, because section 201(ff)(3)(B)(ii) excludes an article authorised for investigation as a new drug once substantial clinical investigations have been instituted and made public.

The second half of the same letter: because the marketing claimed effects on body structure, the products were drugs under section 201(g)(1)(C), then new drugs under 201(p) with no approved application, then misbranded for lacking adequate directions for use.

The current agency line: FDA's consumer notice, current as of 26 April 2023, states that SARMs cannot be legally marketed in the United States as a dietary supplement or a drug at this time.

What "research use only" did in one later letter: not enough to change the outcome. In a December 2025 warning letter to a different seller, covering LGD-4033, RAD-140, MK-677 and S-23 rather than ostarine, FDA treated the products as unapproved new drugs despite labelling that read "RESEARCH COMPOUND" and "NOT FOR HUM[AN]", on the basis of the website evidence of intended use.

Did the SARMs Control Act ever pass?

No. S. 2895, the SARMs Control Act of 2019, was introduced on 19 November 2019 in the 116th Congress. It would have added a defined SARM category to Schedule III of the Controlled Substances Act, naming ostarine and enobosarm first in its list alongside LGD-4033, LGD-3303, RAD-140, andarine, BMS-564929, LG-121071 and S-23. It was referred to committee and did not become law, and an earlier 2018 version met the same end.

Why that matters for the question: the bill existed because SARMs are not currently scheduled. Its failure is the reason ostarine is a drug-law problem rather than a controlled-substance problem.

Is ostarine banned in sport?

Yes, in and out of competition. The 2026 WADA Prohibited List names enobosarm (ostarine) at S1.2, other anabolic agents, in the entry that reads "selective androgen receptor modulators [SARMs, e.g. andarine, enobosarm (ostarine), LGD-4033 (ligandrol), RAD140, S-23 and YK-11]". Every substance in the S1 class is a non-specified substance, and the list has been in force since 1 January 2026.

The scope of "including, but not limited to": the list names six SARMs and covers the class. A compound not printed by name is not thereby permitted.

What is in a product sold as ostarine?

Often not what the label says, though the published sample was not ostarine-specific. In a chemical analysis of 44 products bought online as SARMs generally, only 23 contained any SARM at all, 17 contained a different unapproved drug, and 4 contained no active compound. The amount on the label matched the amount found in only 18 of the 44, and 11 held substances the label never mentioned (Van Wagoner, 2017).

What that sample showed: for these 44 products, nothing in the supply chain was making the label match the contents. The analysis measured identity and amount against the label; it did not examine any manufacturer's specifications, so we make no claim about what does or does not sit behind an individual product.

What the record still leaves open

Four items, none of them small:

Healthy-population effect. The published randomised data sits in older adults and in cancer-associated wasting, not in young healthy users.
Duration. The two trials on this page ran 12 weeks and up to 113 days. Neither describes longer use, and we have not run a systematic search of the wider literature, so this is a limit of what is reported here rather than a ceiling on the published record.
Liver signal. FDA cites liver injury and acute liver failure among reported harms, and states the real number of adverse events is likely higher because reporting is voluntary and users may not connect symptoms to the product.
Product identity. The 2017 analysis sampled products purchased between February and August 2016, so it is one snapshot of that market at that time.

How this page is sourced

Read at the source: the statutory definition comes from the United States Code, the enforcement position from FDA letters and the agency's own consumer notice, the trial figures from the two published papers, and the sport classification from the official 2026 list text.

Nine sources: three papers with DOIs and PubMed IDs, one statute, one bill, three FDA documents, and one international standard.

Last reviewed: 27 July 2026.

1
Dalton JT, Barnette KG, Bohl CE, et al. 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. J Cachexia Sarcopenia Muscle. 2011;2(3):153-161. doi:10.1007/s13539-011-0034-6. PMID 22031847.
2
Dobs AS, Boccia RV, Croot CC, et al. Effects of enobosarm on muscle wasting and physical function in patients with cancer: a double-blind, randomised controlled phase 2 trial. Lancet Oncol. 2013;14(4):335-345. doi:10.1016/S1470-2045(13)70055-X. PMID 23499390.
3
Van Wagoner RM, Eichner A, Bhasin S, Deuster PA, Eichner D. Chemical composition and labeling of substances marketed as selective androgen receptor modulators and sold via the internet. JAMA. 2017;318(20):2004-2010. doi:10.1001/jama.2017.17069. PMID 29183075.
4
Definition of anabolic steroid, 21 U.S.C. section 802(41). Accessed 27 July 2026. law.cornell.edu, 21 U.S.C. 802.
5
S. 2895, SARMs Control Act of 2019, 116th Congress, introduced 19 November 2019. Referred to the Committee on the Judiciary; not enacted. Accessed 27 July 2026. govinfo.gov, BILLS-116s2895is.
6
U.S. Food and Drug Administration. Warning letter to Panther Sports Nutrition, WL 535341, 23 October 2017. Accessed 27 July 2026. fda.gov warning letter 535341.
7
U.S. Food and Drug Administration. FDA warns of use of selective androgen receptor modulators (SARMs) among teens, young adults. Consumer update, content current as of 26 April 2023. Accessed 27 July 2026. fda.gov consumer update.
8
World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026, section S1.2. Effective 1 January 2026. Accessed 27 July 2026. wada-ama.org, 2026 Prohibited List.
9
U.S. Food and Drug Administration. Warning letter to Prime Sports Nutrition, reference 719433, 12 December 2025. Accessed 27 July 2026. fda.gov warning letter 719433.

Around this page: five neighbouring pages on classification and on what a vial can be shown to contain.

Is MK-677 a SARM: the compound sold beside ostarine that is not in the class at all.
Cardarine (GW501516) explained: the third compound in the same retail bucket, and the toxicology record behind it.
How to read a COA: what a certificate of analysis tests, and what it leaves untested.
What an HPLC purity number misses: why a high percentage on paper answers a narrow question.
The dose-math hub: the arithmetic section, for the pages where numbers do the work.

Where the next one lands: every new statute-and-label read goes out through The Decadewise briefing on the day it is finished.

The disclaimer

Every page is reviewed by medical professionals before it ships, and written with longtime biohackers who were doing this before it was a trend. Reviewed still does not mean prescribed: nothing here is medical advice. It is research, trial data, and reported use, with the numbers intact so you can check them. For decisions about your body, see a doctor who can look at your labs.