YK-11 for Myostatin Inhibition & Lean Mass — SARMs
Hybrid SARM/steroid with myostatin-inhibiting properties via follistatin upregulation. Cell-study only. Extremely limited data. NOT FDA-approved.
Overview
YK-11 is a unique compound that occupies a gray area between selective androgen receptor modulators and anabolic steroids. Structurally, YK-11 possesses a steroidal backbone derived from 19-nordihydrotestosterone (19-nor-DHT), making it more accurately classified as a synthetic steroidal compound rather than a true non-steroidal SARM. YK-11 was first described by Kanno et al. (2011; PMID: 21372378) in a cell-based study using C2C12 myoblasts, where it was shown to act as a partial androgen receptor agonist while simultaneously inducing follistatin expression. Follistatin is a natural glycoprotein that binds and neutralizes myostatin, a powerful negative regulator of muscle growth. By inhibiting myostatin through follistatin upregulation, YK-11 theoretically removes a biological brake on muscle hypertrophy, potentially allowing muscle growth beyond normal physiological limits. However, it is critical to note that ALL published data on YK-11 comes from a single research group using in vitro cell culture models. There are NO animal studies, NO pharmacokinetic studies, and NO human clinical trials. The compound structure includes 17-alpha-alkylation, indicating significant hepatotoxic potential comparable to oral anabolic steroids such as methyltestosterone or stanozolol. The mechanism of myostatin inhibition via follistatin has only been demonstrated in cultured myoblasts and has never been confirmed in a living organism. Claims of extraordinary muscle-building potential are entirely speculative and unsupported by in vivo evidence. YK-11 is NOT FDA-approved, has no regulatory status, and is prohibited by WADA. The compound represents one of the least-studied substances in the performance enhancement pharmacopeia, and its use carries entirely unknown risks.
Indications
- In vitro research into follistatin-mediated myostatin inhibition (PMID: 21372378)
- Cell culture studies of partial AR agonism combined with gene expression modulation
- Theoretical investigation of dual-mechanism muscle growth compounds
- Basic research into myostatin biology and follistatin regulation
- No clinical or even preclinical (animal) investigations conducted
Mechanism of Action
YK-11 is administered orally. 17-alpha-alkylation provides oral bioavailability but confers hepatotoxic risk. Steroidal 19-nor-DHT backbone distinguishes it from true non-steroidal SARMs. No pharmacokinetic parameters established
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| YK-11 | 5 mg/day | Split twice daily (estimated) | Arbitrary dose — no pharmacokinetic data to support any dosing regimen |
| YK-11 | 10 mg/day | Split twice daily (estimated) | Commonly reported gray-market dose; entirely without scientific basis |
| YK-11 | 15 mg/day | Split twice daily (estimated) | Higher dose; increased hepatotoxicity risk with 17-alpha-alkylated structure |
Evidence Grade
GRADE D
Safety & Contraindications
- NOT FDA-approved — NO animal or human studies exist
- ALL published data from single in vitro cell culture study — extremely limited evidence base
- 17-alpha-alkylated steroidal structure — expected significant hepatotoxicity
- Not a true SARM — steroidal backbone (19-nor-DHT derivative) despite marketing
- Myostatin inhibition via follistatin NEVER confirmed in vivo
- Unknown pharmacokinetics — no half-life, bioavailability, or metabolite data
- Unknown HPG axis suppression profile — steroidal structure suggests significant suppression
- Gray-market only — no quality control, no standardized dosing
- Potential for severe androgenic side effects due to steroidal nature
- WADA prohibited substance
- Highest uncertainty-to-risk ratio of any commonly marketed SARM
- Absolutely no basis for any dosing recommendation — all doses are arbitrary