LibrarySARM · AAS

YK-11

Also: YK11, YK 11

Marketed as a SARM but structurally a 17α-methylated DHT derivative acting as a myostatin inhibitor; its side-effect profile is closer to an oral AAS. Hepatotoxic, with liver strain the dominant reported concern. WADA-banned. Research chemical reference only.

Suppressive · moderate to substantialHepatotoxicity: highWADA-banned · 14d detection window

Why hepatotoxic: 17α-methylated structure, the same modification that makes oral steroids like Dianabol and Anadrol hepatotoxic.

Classification note. Sold and categorized as a SARM, but structurally a 17α-methylated DHT derivative whose primary mechanism is myostatin inhibition. Its side-effect profile is more similar to oral AAS than to true SARMs; treat it with the caution appropriate to a methylated oral steroid.

Limited human clinical data: dosing extrapolated from animal studies and user reports.

Not FDA-approved for human use. WADA-banned for tested athletes. Sold as a research chemical; clinical safety beyond short-term trials is not established. This page is educational reference only, not a recommendation or endorsement of use.

PK quick reference
Half-life
8 h
Route
Oral
Compound-specific warnings
  • Not a true SARM despite being marketed as one; treat with caution appropriate to oral AAS.
  • 17α-methylation makes it hepatotoxic. ALT/AST elevations commonly reported.
  • Liver strain is the dominant risk; ALT and AST are the markers that track it.
  • DHT-derived structure can accelerate male-pattern baldness in susceptible individuals.

Important classification note

YK-11 is not really a SARM. It's sold as one and grouped with SARMs in user communities, but structurally and pharmacologically it's a steroidal compound:

  • Structurally: A synthetic derivative of 5α-dihydrotestosterone (DHT) with a 17α-methyl group
  • Mechanism: Acts as a weak partial agonist at the androgen receptor, but its primary mechanism is believed to be myostatin inhibition (myostatin is the protein that limits muscle growth — inhibiting it allows more growth)
  • Side effects: Behave like an oral anabolic steroid (hepatotoxic, suppressive) rather than a true SARM

The 17α-methyl group is the same modification that makes oral steroids like Dianabol and Anadrol hepatotoxic. Treating YK-11 like a "gentle SARM" is a category error that has put users in liver-injury territory.

This entry is included because users will search for it under SARMs, but the safety profile is much closer to an oral AAS. Treat it accordingly.

Overview

YK-11 was characterized in 2011 by Yuichiro Kanno's research group in Japan (hence "YK"). It was originally studied as a potential treatment for muscle wasting disorders, with early in vitro work suggesting myostatin inhibition as a primary mechanism. Human clinical data is essentially nonexistent — all dosing and safety information comes from animal/in vitro work and user self-reports.

In user communities it has a reputation for significant strength gains and a hardening effect, but with side effects more typical of oral AAS than other SARMs.

Mechanism

Two proposed mechanisms:

  1. Weak partial agonist at the androgen receptor — contributes some direct anabolic signaling
  2. Myostatin inhibition — increases follistatin expression in cell culture studies, which would inhibit myostatin and allow greater muscle hypertrophy

The myostatin inhibition mechanism is theoretical in humans — well-characterized in cell models, not validated in human trials.

Pharmacokinetics

  • Half-life: unknown in humans; estimated 6-10 hours, with no published human pharmacokinetic study to confirm it
  • Tmax (oral): estimated 1-2 hours
  • Bioavailability (oral): unknown; assumed moderate to high
  • Metabolism: hepatic, first-pass; 17α-methylation slows hepatic breakdown (the source of both its oral activity and its hepatotoxicity)
  • Elimination: urinary

YK-11 has never been evaluated in a human clinical trial, so there is no clinical reference for human use of any kind.

Expected effects

  • Lean mass gain (modest to moderate) reported
  • Significant strength gains reported
  • Hardening / density in physique
  • Joint discomfort sometimes reported

Side effect profile

Behaves like an oral AAS, not a SARM:

  • Hepatotoxicity: This is the defining concern. 17α-methylation makes YK-11 hepatotoxic in the same way as Dianabol, Anadrol, or other oral steroids. Significant ALT/AST elevations are commonly reported. Liver strain from 17α-methylated compounds scales with both the amount and the duration of exposure. Elevated liver enzymes are a marker to discuss with your healthcare provider, and decisions about liver-protective management should be made with a qualified healthcare provider.
  • HPTA suppression: Moderate to substantial, with suppressed LH, FSH and total testosterone documented in user bloodwork. Recovery of the axis is a clinical question for a qualified healthcare provider.
  • Lipid changes: Notable HDL reductions, LDL elevation — similar pattern to oral AAS.
  • Hair loss: As a DHT derivative, YK-11 can accelerate male pattern baldness in susceptible individuals.
  • Acne: Possible, given DHT-derived structure.

Bloodwork monitoring

Given YK-11's hepatotoxic profile, reported monitoring protocols align with what is used for oral AAS rather than milder SARMs. Markers to monitor include a baseline panel, a liver-focused check around 3 weeks in, an end-of-cycle panel, and a post-cycle panel at approximately 4 weeks:

  • Total + Free Testosterone
  • LH, FSH
  • Estradiol (sensitive)
  • SHBG
  • Full lipid panel
  • ALT, AST, GGT, total bilirubin (mandatory — liver is the primary concern)
  • CBC

Interactions

  • Hepatic load is additive. Alongside other 17α-methylated orals, or anything else cleared hard by the liver, the burden on liver markers compounds rather than staying flat.
  • Lipid effects add in the same way: HDL reduction and LDL elevation are shared effects of oral 17α-methylated compounds.
  • Androgenic effects and HPTA suppression add to those of any other androgen present, including prescribed testosterone.

Pharmacokinetic modeling parameters

ka: 1.5 /day
ke: 2.1 /day
Vd: 60 L
F: 0.70
half_life_hours: 8

Notes and caveats

  • The "SARM" classification is misleading. YK-11 is a methylated steroid with myostatin-inhibiting properties. It should be treated with the caution appropriate to oral AAS, not the relative permissiveness applied to true SARMs.
  • The 17α-methylation creates a real hepatotoxicity burden; decisions about liver-protective management should be made with a qualified healthcare provider.
  • The myostatin inhibition mechanism is well-established in cell culture but has not been validated in human trials — claims about specific muscle growth percentages from "myostatin inhibition" are extrapolation.
  • Some users report a flat or muted feel compared to other SARMs (less of a noticeable "kick"), which community harm-reduction discussions note has been associated with dose-escalation and corresponding side effect amplification.