YK-11

Mechanism of Action

YK-11 is a synthetic steroidal compound classified as a gene-selective partial agonist of the androgen receptor. Uniquely among SARMs, YK-11 does not induce the N/C terminal interaction of the AR required for full transcriptional activation, instead selectively activating a subset of AR-dependent genes. Its primary distinguishing mechanism is potent induction of follistatin expression, which directly antagonizes myostatin — a key negative regulator of skeletal muscle mass. This dual action (partial AR agonism + myostatin inhibition via follistatin) theoretically provides anabolic stimulus beyond what full AR agonists alone can achieve.

Dosing Protocol

Notes

YK-11 has the weakest evidence base of any compound in this database — only in vitro and limited in vivo animal studies exist. The follistatin/myostatin mechanism is compelling but entirely unvalidated in humans. The steroidal 17-alpha-alkylated structure carries inherent hepatotoxicity risk similar to oral anabolic steroids (methyltestosterone, superdrol). CRITICAL: Liver monitoring is absolutely mandatory and should be more frequent than for other SARMs given the structural hepatotoxicity risk. Required bloodwork: Liver function panel (AST, ALT, GGT, bilirubin, ALP) at baseline, 2 weeks, 4 weeks, and end of cycle. Total testosterone, free testosterone, LH, FSH, estradiol. CBC. Lipid panel. If ALT/AST exceed 3x upper limit of normal, discontinue immediately. PCT mandatory. Medical supervision required.

Stacking

• MK-677 (non-suppressive GH elevation to complement anabolic effect)
• NAC / TUDCA (liver protection — essential for steroidal SARM)
• Cardarine GW-501516 (endurance without additional suppression)

Interactions

• Testosterone / AAS [MEDIUM] — Additive HPG suppression. YK-11 is structurally a steroid and suppresses endogenous testosterone.
• Hepatotoxic agents [HIGH] — YK-11 is a methylated (17-alpha-alkylated) steroidal compound with significant hepatotoxic potential. Do not combine with other hepatotoxic drugs.
• Myostatin-targeted therapies [LOW] — Theoretical additive myostatin inhibition — no data on combined use.

Contraindications

• Pre-existing liver disease
• Androgen-sensitive cancers
• Cardiovascular disease
• Pregnancy and breastfeeding
• Individuals under 21
• Anyone unwilling to accept research chemical risk with zero human clinical data

Side Effects

• Testosterone suppression (expected — steroidal compound)
• Hepatotoxicity (17-alpha-alkylated structure implies liver toxicity risk)
• Joint pain and tendon issues (anecdotal — possibly from DHT-like drying effects)
• Hair loss (steroidal androgenic effects)
• Aggression
• Unknown long-term effects (no human studies)

Key Papers

• 10.1248/bpb.b13-00535
• 10.1016/j.bbrc.2021.01.099
• 10.1016/j.cbi.2024.110895

Source Quality

Not FDA-approved. Research chemical only with zero human clinical data. Extreme caution warranted. Source only from vendors with full third-party analytical testing (HPLC, NMR identity verification). High adulteration risk in consumer market.

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