Section 1 of 9Overview
Overview
MK-3984 is a nonsteroidal selective androgen receptor modulator (SARM) developed by Merck & Co. — a small-molecule drug that binds the androgen receptor (AR). It is not a peptide and not a steroid. Chemically it is an aryl-propanamide (diarylpropanamide), the same chemotype family as ostarine and andarine, and distinct from the steroidal (4-azasteroid) SARMs (PubChem CID 44555928).
Human exposure is limited. The only human data located come from a single reported 12-week Phase 2 trial in 88 postmenopausal women, presented at the 2010 Endocrine Society Annual Meeting (ENDO 2010) and in a GTx company release. No ClinicalTrials.gov registration (NCT number) for this trial was located — the trial exists in the record as a conference presentation / company communication, not as a verified registered study or a peer-reviewed publication.
Development was discontinued around 2010, consistent with Merck exiting the SARM field. MK-3984 is not an approved medicine anywhere, and has never been approved by the FDA, EMA, or any regulator.
[!WARNING] MK-3984 is a discontinued investigational research chemical, not a human-use product. It is not a "milder", "safer", or "legal" alternative to anabolic steroids. It has never been approved by any regulator; its one reported human trial found a compound-specific liver-enzyme signal that its comparator did not have; and — like all SARMs — it is banned in sport (WADA S1.2). Material sold online as "MK-3984" is frequently mislabelled or contaminated (see Safety). This page is a factual summary for research context and is not medical or legal advice (as of 2026).
Section 2 of 9Chemistry and structure
Chemistry and structure
| Property | Value |
|---|---|
| Name | MK-3984 |
| Class | Nonsteroidal SARM — aryl-propanamide (diarylpropanamide) small molecule (not a peptide, not a steroid) |
| IUPAC name | (2R)-3,3,3-trifluoro-N-[[2-fluoro-5-(trifluoromethyl)phenyl]methyl]-2-hydroxy-2-phenylpropanamide |
| Molecular formula | C17H12F7NO2 |
| Molecular weight | 395.27 g/mol |
| CAS number | 871325-55-2 |
| PubChem CID | 44555928 |
| InChIKey | YSMGNNKNGUPHCD-OAHLLOKOSA-N |
| Half-life | Not established / not found in sources |
Section 3 of 9Mechanism of action
Mechanism of action
- Selective androgen receptor modulator. MK-3984 binds the androgen receptor (AR) and is classified verbatim as a SARM in PubChem, Wikipedia, and multiple pharmacology sources. The SARM design goal is tissue-selective agonism — anabolic effects on skeletal muscle and bone while aiming to spare prostate and other androgenic tissues. [Human]/[Animal]
- Aryl-propanamide chemotype, not steroidal. The PubChem structure (SMILES
C1=CC=C(C=C1)C(C(=O)NCC2=C(C=CC(=C2)C(F)(F)F)F)(C(F)(F)F)O; a hydroxy-trifluoromethyl propanamide with two aryl groups) places MK-3984 in the same diarylpropanamide class as ostarine and andarine — distinct from steroidal SARMs. [In vitro] - Tissue-selectivity signal in humans. In the ENDO 2010 postmenopausal-women trial, MK-3984 did not stimulate endometrial proliferation (no increase in endometrial thickness) over 12 weeks, reported alongside lean-mass and strength effects comparable to ostarine. [Human]
Section 4 of 9Research and evidence
Research and evidence
Human data on MK-3984 come from a single reported 12-week Phase 2 trial, and the record is a conference presentation / company release — not a registered trial or a peer-reviewed paper.
| Trial | Population | Design | Outcome |
|---|---|---|---|
| ENDO 2010 head-to-head (GTx company release; no NCT located) | 88 postmenopausal women | Randomized, 12 weeks; MK-3984 50 mg and 125 mg vs ostarine 3 mg vs placebo | Lean body mass rose +1.54 kg (MK-3984 50 mg) and +1.74 kg (MK-3984 125 mg) vs placebo — comparable to ostarine 3 mg (+1.54 kg). The ostarine arm also showed a leg-press strength increase (~22 lb from baseline). Efficacy on lean mass/strength described as comparable between MK-3984 and ostarine. MK-3984 showed a compound-specific liver-enzyme signal (see Safety). |
| Development status | — | — | No longer being developed; discontinued around 2010, consistent with Merck exiting the SARM space. Never approved by any regulator. |
Honest read of the evidence. MK-3984's efficacy claim rests on one small, short, unpublished, unregistered trial reported via a company release. There is no peer-reviewed primary publication (no PMID) located, no ClinicalTrials.gov NCT number located, and no pharmacokinetic, long-term, carcinogenicity, cardiovascular, or reproductive data. The lean-mass numbers should be read as reported-but-unverified company/conference figures, and the compound was abandoned rather than advanced.
Section 5 of 9Status and regulation
Status and regulation
- Not approved anywhere. MK-3984 is not an approved drug in the United States, the EU, or elsewhere, for any indication.
- Discontinued. Development stopped around 2010; no active program has been located. Highest reported phase is Phase 2, on conference/company-release data only.
- WADA status (separate axis). Like all SARMs, MK-3984 is prohibited in sport at all times, in and out of competition, under WADA S1.2 (Anabolic Agents — Other Anabolic Agents / SARMs). Any SARM triggers an anti-doping violation even if not individually named on the list.
Section 6 of 9Safety
Safety
Human safety data specific to MK-3984 are limited to the single reported 12-week trial. The signals below combine that trial observation with class-level SARM safety data.
- Compound-specific hepatotoxicity / drug-induced liver injury (DILI). In the 88-woman Phase 2 trial, seven subjects treated with MK-3984 were discontinued due to liver enzyme elevations greater than three times the upper limit of normal, whereas no clinically significant liver enzyme elevations occurred with ostarine. This direct human liver signal distinguished MK-3984 from its comparator and is a plausible contributor to discontinuation. [Human]
- Class-level hepatotoxicity / DILI. The FDA has warned that SARM-containing bodybuilding products have caused life-threatening reactions including liver injury requiring hospitalization, and (per NIH LiverTox and case reports) acute liver injury in cholestatic and hepatocellular patterns, with acute liver failure described in the class. [Human]
- Testosterone / HPTA suppression (class). Suppression of endogenous testosterone and the hypothalamic-pituitary-testicular axis is a recognized androgen-receptor-agonist class effect. Compound-specific HPTA data for MK-3984 were not found — the magnitude for this compound is not established. [Human]/[Hypothesis]
- Absence of data is itself a risk. There is no dedicated long-term human safety, carcinogenicity, cardiovascular, or reproductive-toxicity dataset for MK-3984; human exposure is one 12-week trial, and most safety inference is class-level, not compound-specific. [Hypothesis]
The contamination reality. In a landmark analysis, Van Wagoner et al. (JAMA 2017;318(20):2004-2010, PMID 29183075) chemically tested products sold as SARMs: only 52% actually contained the labelled SARM, 39% contained a different unapproved drug, 9% contained no active compound at all, and roughly 59% contained an amount differing from the label. A "SARM" label is not a reliable statement of contents — a product a consumer buys as "MK-3984" may not be MK-3984.
[!WARNING] There is no established safe dose of MK-3984 for human use. Its one reported human trial produced a liver-enzyme signal serious enough to discontinue seven subjects, its long-term risks are uncharacterized (unknown human half-life, unquantified HPTA effects), and a product sold as MK-3984 may contain a different drug, no drug, or a wildly inaccurate dose. Do not treat any SARM as a benign supplement.
Section 7 of 9Legal status
Legal status
The legal status of MK-3984 is not assessed here and varies by jurisdiction. Across many countries SARMs are not approved for human consumption and are handled as unapproved investigational drugs or research chemicals; some markets restrict or prohibit their sale for human use. This page frames MK-3984 only as a research reagent, makes no claim about the legality of human use anywhere, and does not constitute legal advice. Note that anti-doping status (WADA) is a separate axis from legality: a substance can be legal to possess yet still banned in sport.
Section 8 of 9How it compares
How it compares
MK-3984 sits in the same nonsteroidal aryl-propanamide SARM family as several better-known research compounds — all androgen receptor modulators, none an approved medicine, all prohibited under WADA S1.2:
- Ostarine (MK-2866) — the direct comparator in MK-3984's only human trial, and the most-studied SARM; in that trial it matched MK-3984 on lean mass without the liver-enzyme signal.
- Andarine (S-4) — an early aryl-propanamide SARM from the same chemotype family.
- Testolone (RAD-140) — a potent nonsteroidal SARM with documented liver-injury case reports.
Section 9 of 9Common misconceptions
Common misconceptions
- "It's a peptide." No. MK-3984 is a small-molecule nonsteroidal SARM (an aryl-propanamide), not a peptide.
- "It's a safer, legal steroid." No. It is an unapproved, discontinued investigational drug, and its one human trial found a liver-enzyme signal that its comparator did not have. It is banned in sport (WADA S1.2).
- "It's a well-studied Merck drug." No. Its human evidence is a single 12-week trial in 88 women, reported only as a conference presentation / company release — no NCT registration and no peer-reviewed publication were located.
- "It was just as safe as ostarine." No. On efficacy it matched ostarine, but seven MK-3984 subjects were discontinued for liver enzymes greater than 3x the upper limit of normal, while ostarine caused no clinically significant elevations.
- "There's dosing data for it." There is no established human dose, half-life, or pharmacokinetic profile for MK-3984 in the located sources. The 50 mg and 125 mg figures are trial arms, not a validated dose.