YK-11

YK-11 is a synthetic steroidal compound — structurally a DHT derivative, not a non-steroidal SARM like ostarine or RAD-140. It's sold and used as a SARM because its pharmacology is gene-selective at the androgen receptor, but mechanistically it sits closer to a mild oral anabolic with a bonus follistatin-inducing trick. That dual action — partial AR agonism plus follistatin-mediated myostatin suppression — is what people are actually paying for.

Partial, Gene-Selective Androgen Receptor Agonism#

YK-11 binds the androgen receptor and drives nuclear translocation, but it does not produce the full amino/carboxyl-terminal (N/C) interaction that DHT and testosterone trigger. That N/C interaction is what switches on the full DHT transcriptional program — including many of the genes responsible for classic androgenic effects. YK-11 activates a subset of AR target genes while blocking the DHT-driven N/C conformation, which is the molecular basis for its "selective" label.

"These results indicate that YK11 is a gene-selective partial agonist of AR, which promotes AR nuclear translocation but does not induce full N/C interaction, unlike DHT." — Kanno Y. et al., Biological and Pharmaceutical Bulletin, 2011

Practically: you get muscle and bone anabolism from the activated gene subset, with a different side-effect fingerprint than a full AR agonist — though "different" is not "absent." YK-11 is still suppressive, still lipid-hostile, and still shed-capable in AR-sensitive scalp tissue.

Follistatin Induction and Myostatin Blockade#

This is the mechanism that built YK-11's reputation. In C2C12 myoblasts, YK-11 — unlike DHT — drives follistatin expression, and the hypertrophic differentiation it produces is abolished when follistatin is neutralized with an anti-Fst antibody. Follistatin is an endogenous binding protein that sequesters myostatin (GDF-8) and related TGF-β ligands that normally cap muscle growth. Raise follistatin, you lower free myostatin, you remove a brake on hypertrophy.

"Our data suggest that YK11 increases myogenic differentiation in C2C12 cells by increasing expression of follistatin, a known inhibitor of myostatin." — Kanno Y. et al., Biological and Pharmaceutical Bulletin, 2013

Translation for the user: this is why YK-11 produces the "dry, hard, full" aesthetic people chase with it, and why stacking it into the last 4–6 weeks of a recomp run is a common move. Caveat — this effect has been demonstrated in cell culture, not in controlled human trials. The follistatin story is real; the magnitude in vivo in trained humans is extrapolated.

Osteoblast Activation via AR-Akt Signaling#

YK-11 also drives osteoblast proliferation and differentiation through AR-dependent activation of the Akt pathway, with upregulation of alkaline phosphatase and osteocalcin in MC3T3-E1 cells.

"These results suggest that YK11 up-regulates proliferation and differentiation of MC3T3-E1 cells via AR-dependent activation of the Akt signaling pathway." — Yatsu T. et al., Biological and Pharmaceutical Bulletin, 2018

This is the same broad tissue effect most SARMs show, and it matters most in two scenarios: aggressive cuts where bone-loading drops along with calories, and older users where bone density is already a concern. Don't cycle YK-11 for bone support alone, but count it as a real secondary benefit.

Metabolism and the Methyl Ester#

YK-11 is an orally active steroid ester. In humans, the C-21 methyl ester is cleaved quickly post-ingestion, and multiple hydroxylated and conjugated metabolites are generated.

"The methyl ester at position C-21 was rapidly cleaved in vivo, resulting in the detection of the free acid and its metabolites in human urine samples." — Piper T. et al., Drug Testing and Analysis, 2018

Two practical implications. First, the parent compound has a short effective window, which is why twice-daily dosing (AM/PM, with food) is the community default at 10+ mg/day — it smooths plasma levels given an estimated 6–10 h half-life. Second, the oral-steroidal structure + first-pass hepatic metabolism means liver stress is real in a way it is not for non-steroidal SARMs. This is why TUDCA 500 mg/day is standard during cycles and why stacking YK-11 with other hepatotoxic orals (superdrol, anadrol, heavy dbol) is not advised without active LFT monitoring.

Off-Target: Oxidative Stress in CNS Tissue#

Worth flagging because it shapes how long you should run it. Rodent work from Dahleh and colleagues shows that YK-11 administration produces measurable oxidative damage and mitochondrial dysfunction in hippocampal tissue, with associated behavioral changes.

"We demonstrated that YK11 administration increases oxidative damage and mitochondrial dysfunction in rat hippocampus, raising concerns about its neurotoxicity." — Dahleh M.M.M. et al., Journal of Steroid Biochemistry and Molecular Biology, 2023

Users anecdotally report lethargy and mild mood flattening at the top of the dose range, which lines up directionally with these findings. This is a strong argument against long runs — keep cycles to 6–8 weeks, respect the minimum 8-week off period, and don't treat YK-11 as a blast-and-cruise compound. Used as intended — a short, targeted recomp or finishing tool inside a properly monitored protocol — the risk/reward stays on the right side.

Common (most users)#

• HPTA suppression — YK-11 is steroidal and suppressive. Expect LH/FSH and total test to drop over an 8-week run. Mitigation: plan PCT from day one (nolvadex 20/20/10/10 or enclomiphene 12.5 mg/day for 4 weeks), start the day after last dose.
• Lipid shifts — HDL drop and LDL rise are the norm, consistent with an oral steroidal compound. Mitigation: baseline lipid panel, mid-cycle recheck, cardio 3x/week, and keep saturated fat moderate. Citrus bergamot 1000 mg/day and a fish oil base help blunt the hit.
• Joint / tendon dryness — commonly reported, mechanism unclear. Mitigation: don't stack with other "drying" compounds (winstrol, masteron) in the same block if you're already beat up. Hydration, collagen 15 g/day, MK-677 as a stack partner all help.
• Mild lethargy at 10+ mg/day, especially in the first 1–2 weeks. Mitigation: split the dose BID with food, keep caffeine and training intensity normal — it usually settles.
• Hair shedding in genetically predisposed users — YK-11 activates AR in scalp tissue and behaves more like an AAS than like ostarine here. Mitigation: topical antiandrogen (RU58841) or keep a finasteride base if you already run one. Oral fin won't fully block a steroidal AR agonist but still helps at the systemic level.

Uncommon (dose-dependent or individual)#

• Elevated ALT/AST — more likely above 10 mg/day, past week 6, or when stacked with other orals. Back off if ALT/AST exceed ~2x ULN. TUDCA 500 mg/day on cycle is cheap insurance given the steroidal oral structure.
• Mood flattening / low motivation — reported at higher doses and longer runs. The Dahleh rodent data gives a plausible mechanism:

"We demonstrated that YK11 administration increases oxidative damage and mitochondrial dysfunction in rat hippocampus, raising concerns about its neurotoxicity." — Dahleh 2023, J Steroid Biochem Mol Biol

Translating rodent hippocampal oxidative stress to human mood is an extrapolation, not a proven effect — but if you notice flattening, drop the dose or end the cycle.

• Blood pressure creep — tied to the lipid and water-retention profile. Check BP weekly; if resting climbs into Stage 1 hypertension, add telmisartan 20–40 mg or end the run.
• Erectile function decline / low libido late cycle — the suppression catching up. Low-dose daily tadalafil (5 mg) handles the vascular side; the libido side resolves with PCT.
• Hematocrit rise — less pronounced than with testosterone but possible at higher doses. Check CBC mid-cycle; donate blood if HCT pushes past 52%.

Rare but serious#

• Cholestatic or hepatocellular liver injury — rare but documented signal in user bloodwork, especially at 15+ mg/day, runs past 8 weeks, or stacked with hepatotoxic orals (superdrol, anadrol, heavy dbol). Warning signs: dark urine, pale stools, right upper-quadrant pain, scleral icterus, ALT/AST >5x ULN. Stop the cycle immediately and get a hepatology workup.
• Severe lipid derangement — HDL crashing below 20 mg/dL or LDL doubling. Stop the cycle, give it 8–12 weeks off, and don't re-run without a plan.
• Cardiac events — no direct reports tied to YK-11 specifically, but the lipid and BP profile stacks onto baseline cardiovascular risk. If you already have a family history of early MI or known dyslipidemia, this is not your compound.
• Persistent HPTA suppression past a standard PCT — uncommon but possible with back-to-back cycles or skipped PCT. Warning signs: libido still flat, morning wood absent, and total test still <300 ng/dL at 8 weeks post-PCT. Restart protocol with an endocrinologist, not another blast.

Hard contraindications#

• Active liver disease or baseline elevated LFTs — do not start. YK-11 is steroidal, oral, and metabolized heavily, with the C-21 methyl ester cleaved to its free acid in vivo (Piper 2018, Drug Test Anal). A stressed liver has no business processing it.
• Stacking with other hepatotoxic orals without monitoring — superdrol, anadrol, high-dose dbol, tbol. If you insist on combining, treat the stack as a 2-oral protocol: TUDCA 500 mg/day, shorter cycle (≤6 weeks), bloods every 3–4 weeks.
• Untreated hypertension or dyslipidemia — fix these first. The HDL hit is real and additive on baseline cardiovascular risk.
• Plans for near-term conception — suppression plus unknown effects on spermatogenesis. Wait until post-PCT recovery is confirmed by bloods and semen analysis.
• Female use for physique — avoid entirely. YK-11 is a steroidal AR agonist with no characterized female dosing, and the partial-agonist mechanism

"indicate that YK11 is a gene-selective partial agonist of AR, which promotes AR nuclear translocation but does not induce full N/C interaction, unlike DHT." — Kanno 2011, Biol Pharm Bull

still drives AR-dependent transcription. Virilization risk is mechanistically plausible and entirely uncharacterized.

• Pregnancy — teratogenic potential unknown; a steroidal AR agonist is an automatic no.
• Underage users — AR activity during ongoing epiphyseal closure and HPTA maturation is a line that does not get crossed.

Gender and PCT notes#

Women: not recommended. There is no safe-dose data and the compound's steroidal AR agonism makes virilization (clitoral enlargement, voice deepening, hirsutism) a realistic risk with no way to predict threshold. Ostarine at low dose is the community default for female SARM use, not YK-11.

Men — PCT: mandatory after any cycle ≥4 weeks. Standard protocol is nolvadex 20/20/10/10 mg or enclomiphene 12.5 mg/day for 4 weeks, starting the day after last dose. Bloodwork at week 8 post-PCT confirms recovery — total test, free test, LH, FSH, estradiol. Do not start another suppressive cycle until those are back in baseline range. A minimum of 8 weeks off (time on + PCT = time off) between YK-11 cycles is the community floor, and frankly the people running it every 12 weeks look like it.

Fertility: if conception is on the 6–12 month horizon, skip YK-11 this year. There is no human reproductive-safety data, and the combination of suppression plus unknown spermatogenic effects is not worth the cycle.