YK-11

Structure: Steroidal SARM. YK-11 is a synthetic derivative of 5-alpha-dihydrotestosterone (DHT) with a norpregnadiene backbone. Unlike non-steroidal SARMs, it shares structural features with anabolic steroids, which likely underlies its hepatotoxicity risk. It is classified as a SARM due to its tissue-selective partial AR agonism, but it is chemically closer to a steroid than to compounds like ostarine or LGD-4033.

Dual Mechanism:

• Partial androgen receptor agonism: activates AR in muscle and bone with some tissue selectivity
• Myostatin inhibition: Kanno et al. (2013) demonstrated that YK-11 induces follistatin expression in C2C12 myoblasts in vitro, which inhibits myostatin (a negative regulator of muscle growth). This effect has not been confirmed in vivo in humans.

Dosage:

• Bodybuilding (anecdotal): 5-15 mg/day for 8-12 weeks
• Typically split into 2 doses/day due to short estimated half-life
• No clinical doses exist

Administration:

• Oral. Available as raw powder, liquid suspension, or capsule (research-chemical grade only).
• Split dosing (morning and evening) is common due to the short estimated half-life.

Key Notes:

• The only published mechanistic data is Kanno et al. (2013): an in vitro cell study demonstrating follistatin induction and myostatin inhibition in mouse muscle cells. No human or animal in vivo data exists.
• Steroidal backbone strongly suggests hepatotoxicity risk comparable to oral anabolic steroids. No human case reports published as of early 2026, but the structural similarity to 17-alpha alkylated steroids is a significant red flag.
• HPTA suppression is expected to be moderate to severe (steroidal AR agonism), but no quantitative human data exists.
• Completely experimental: no safety, pharmacokinetic, or efficacy data in humans. All reported benefits and risks are extrapolated from structure or anecdotal accounts.
• WADA prohibited under S1 (anabolic agents).
• Liver function tests, testosterone, LH, FSH, and full lipid panel monitoring are essential if used.