YK-11 — Myostatin Inhibitor / SARM Hybrid — SARMs
Steroidal compound with dual SARM and myostatin inhibition properties. Preclinical data only with no human studies.
Overview
YK-11 is a unique steroidal compound that exhibits properties of both a selective androgen receptor modulator (SARM) and a myostatin inhibitor. Structurally derived from 5-alpha-dihydrotestosterone (DHT), YK-11 was first described by Kanno et al. (2011) at Toho University in Japan. In C2C12 myoblast cell culture studies, YK-11 induced myogenic differentiation and increased follistatin expression — a natural myostatin antagonist. By upregulating follistatin, YK-11 theoretically reduces the inhibitory effect of myostatin on muscle growth, potentially allowing for muscle hypertrophy beyond what AR agonism alone could achieve. This dual mechanism is of significant interest because myostatin inhibition has been a long-sought target for treating muscle wasting conditions. However, YK-11's evidence base is extremely limited: there are no in vivo animal studies, no pharmacokinetic data, and absolutely no human clinical trials. All published data consist of a handful of in vitro cell culture experiments. The compound's steroidal backbone suggests potential for hepatotoxicity and endocrine disruption. YK-11 is available on the gray market and used by bodybuilders, but its safety profile is entirely unknown.
Indications
- Investigational: Myostatin inhibition (in vitro data only)
- Unapproved: Muscle growth beyond AR agonism (bodybuilding use)
- No clinical applications — research compound only
Mechanism of Action
YK-11 binds the androgen receptor as a partial agonist, inducing anabolic gene expression in C2C12 muscle cells
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| YK-11 | 5-15 mg | Once or twice daily | Bodybuilding doses — NO scientific basis; purely anecdotal |
Evidence Grade
GRADE D
Safety & Contraindications
- NO in vivo or human data — safety profile completely unknown
- Steroidal structure (DHT derivative) suggests potential hepatotoxicity
- Likely causes HPG axis suppression given steroidal backbone
- Hair loss and prostate effects possible (DHT-derivative concern)
- Myostatin inhibition effects unverified in living organisms
- Extremely limited scientific literature — only a few in vitro papers exist
- Gray market products untested for purity