YK-11

Intro

YK-11 is a synthetic steroidal compound first described in 2011 by Yuichiro Kanno at Toho University.

Its formal chemical name is (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester — a 19-nor-pregnane derivative with an orthoester-derived moiety at the D-ring. The community sells it alongside non-steroidal SARMs like ostarine and LGD-4033, but its structure is closer to a DHT-derived anabolic steroid than a tissue-selective receptor modulator.

Kanno's 2013 paper in Biological and Pharmaceutical Bulletin established the mechanism that drives community interest: YK-11 acts as an androgen receptor partial agonist and induces follistatin expression in C2C12 mouse myoblast cells more strongly than DHT itself. Follistatin is the body's endogenous antagonist of myostatin — the protein that caps how much muscle a person can carry. In theory, raising follistatin lifts the muscle-growth ceiling. The myogenic regulatory factors MyoD, Myf5, and myogenin were activated more by YK-11 than by DHT in the same model, and anti-follistatin antibody fully reversed the effect — the cleanest mechanistic evidence that YK-11's anabolic signal flows through the follistatin/myostatin axis rather than direct AR transcription alone.

The compound never passed preclinical development. No phase 1, 2, or 3 trials. No human case reports in indexed literature. No published pharmacokinetics in humans — community estimates the half-life at 6-10 hours and the peak around 1.5 hours, but these are inferences from felt onset, not measured plasma levels. The published research is entirely preclinical: in vitro work in mouse myoblasts and BMSCs, in vivo rodent studies in bone regeneration and hippocampal function, and the Piper 2018 metabolism study that characterized urinary metabolites for doping control. Despite this, gray-market adoption was substantial through the mid-2010s and continued growing because the dual mechanism (AR + myostatin axis) is unusual and the dry phenotype matches what advanced users want from a finishing compound.

The most consequential new evidence is the Dahleh et al. work from 2023 and 2024 in The Journal of Steroid Biochemistry and Molecular Biology and Chemico-Biological Interactions. Anabolic-dose YK-11 in rats produced oxidative stress, mitochondrial dysfunction, IL-1β and IL-6 elevation, BDNF/TrkB/CREB downregulation, and memory consolidation deficits in the hippocampus. The phrase the authors used: 'YK-11 has similar neurotoxic effects to AAS in hippocampus.' Exercise partially offset some inflammatory markers but did not protect against the core neurotrophic and apoptotic damage. This is the first clinical-grade evidence that YK-11 is not a peripherally-restricted SARM — it crosses the blood-brain barrier and behaves CNS-actively at doses humans actually use.

Current status: WADA and USADA list YK-11 as banned. It remains a unregulated research-market compound with no clinical pathway. Unregulated supply persists, and community use has stayed niche but persistent — particularly as a 'dry hardening' adjunct in late-stage bulking cycles or as a non-injectable alternative to Masteron for users who want a DHT-class effect without pinning.

Observed Effects

Primary intended effects. Community reports converge on a tight, dense, vascular physique shift over 6-12 weeks at 10 mg/day oral.

Effect onset is unusually fast for an anabolic compound — multiple first-person logs report acute strength sensation within the first few doses, not the typical 2-3 week tissue-accumulation window seen with non-steroidal SARMs. One logged 8-week protocol at 10 mg sublingual described 'the weights seemed to lift themselves off the ground' on day one. The most consistent self-reported outcomes are bench press increases of 10-30 lb over 6-8 weeks, hardness/dryness improvements visible within 2 weeks, and 3-8 lb of lean tissue gain in users running it solo at standard dose. Higher-dose logs (15-20 mg/day for 8 weeks) report 8-10 lb lean mass gains, but these are unmeasured by DEXA and dependent on diet/training context.

Bone effects. The 2025 Wang paper in the Journal of Molecular Endocrinology demonstrated dose-dependent osteogenic differentiation of bone marrow-derived mesenchymal stem cells at 0.25-4 μM in vitro, with 2 μM specifically increasing BMSC proliferation. In Sprague-Dawley rats, YK-11-equipped hydrogel at 0.5 and 1 mg/mL promoted cranial defect repair through AR activation and proposed BMP2/Smad signaling. AR antagonism abolished both the in vitro and in vivo bone effects. Whether this translates to clinically meaningful bone density change in healthy adult human users is unstudied.

Secondary effects. Several first-person logs report improved recovery between training sessions (one Anabolic Steroids SA user described 'recovering more quickly' as the dominant subjective effect at 30 days with no acute strength jump). Skin shifts toward dry — sometimes desirable, sometimes problematic. Pumps and muscle cramping in arms are commonly reported, severe enough to require electrolyte and taurine supplementation. Some users describe sleep changes (lighter, more vivid dreams) but this is not consistently documented.

What does not happen. Scale weight gains in the 15-25 lb range that some retail-affiliated guides promote are not supported by documented logs from experienced users. The dry phenotype means less water retention than testosterone or AAS — so when users move from a wet AAS cycle onto YK-11, the scale often drops while body composition improves. Some users report essentially null results despite running multiple product batches.

Interindividual variation is wide. The same 10 mg/day dose produces dramatic strength response in one user and 'waste of money' in another, even when sourced from supposedly verified product batches. Product variability cannot be ruled out as a cause, but it is unlikely to fully explain the variance — Kanno's 2013 paper suggests the follistatin response itself may depend on baseline AR sensitivity, which differs across users.

Field Reports

What works for experienced users. Solo or low-stack 10 mg/day BID for 6-8 weeks during a cutting/hardening phase produces the most consistent positive reports — dry physique shift, vascularity gain, late-cycle plateau breaks, fast strength onset. Users at moderate body fat (12-18%) running a base of test or stacked with a non-steroidal SARM see the cleanest results.

What disappoints. First-time PED users running YK-11 as their initial compound consistently report worse outcomes than experienced users — community moderators explicitly warn against this entry point. Users above 22% body fat see minimal aesthetic return because the dry hardening signature requires already-low body fat to be visible. Users running YK-11 inside heavy AAS stacks struggle to identify isolated effect, with one practitioner publicly framing 7-week 30 mg/day inside a multi-compound cycle as 'still not convinced it's doing anything.'

Common protocol mistakes. Skipping PCT thinking YK-11 is 'just a SARM' — confirmed bloodwork data show real LH/FSH suppression that requires full SERM PCT. Ignoring tendon symptoms because they appear in week 1-3 rather than later — early tendon stress is the dominant injury pattern, and continuing through it has produced complete muscle tears in extreme cases. Running high-dose protocols (20-30 mg/day) on first cycle — side effects scale steeply above 15 mg/day and there is no documented benefit to that ceiling for first-time users.

Refinements experienced users make. Sublingual administration of oral liquid for better absorption. Starting at 5 mg/day for the first week to test individual response before escalating. Continuing cardarine through PCT for cortisol suppression rather than dropping it at cycle end. Pre-cycle 3-day fasting protocols (used by some SARM community moderators) for hunger reset before introducing the appetite changes that come with stack adjuncts like MK-677. Running mid-cycle ALT measurements rather than relying on hepatic protection supplements alone.

The dryness paradox. Many users report skin and vascularity dryness as a desirable cosmetic effect during the cycle, but some experience the dryness as uncomfortable and persistent — one anabolic-community user reported skin dryness and reduced vein prominence that lasted after discontinuation. The same physiological effect maps to opposite subjective experiences depending on user expectations.

Cost vs. effect calibration. A clean YK-11 cycle with full PCT, cardarine, liver support, and mid-cycle bloodwork costs roughly $150-300. For users targeting 3-6 lb of lean tissue and a hardening shift, this is a reasonable price. For users expecting 15-25 lb scale gains, the disappointment is structural — the compound does not deliver that magnitude, the marketed claims do not match documented outcomes, and the money is better spent on a longer cycle of a more validated compound.

Community Consensus

YK-11 occupies an unusual niche in the unregulated bodybuilding community. It is technically a steroid that gets sold as a SARM, structurally an androgenic steroidal compound that activates the AR differently from the rest of the SARM shelf, and a unregulated research-market compound that never made it to clinical development despite persistent interest from advanced physique users.

The reputation is split. Evidence-aware practitioner discussion treats the mechanism as real but the human evidence as thin: no trials, no indexed human case reports, no measured human pharmacokinetics, and no long-term endocrine, cardiovascular, hepatic, or neurological outcomes. The more aggressive community pitch frames it as an oral hardening tool with a myostatin-axis edge; the more skeptical read is that Anavar or Masteron cover the same visible phenotype with more history and cleaner interpretability.

A stable protocol envelope exists despite the absence of clinical guidance. The common template is 10 mg/day split BID for 6-8 weeks, full SERM PCT, liver and cardio support, and mid-cycle bloodwork at week 4-6 focused on ALT/AST, lipids, and HPTA markers. Disagreement remains around bulking versus cutting use, ostarine versus RAD-140 as the base compound, 8-week versus 12-week duration, and whether YK-11 contributes enough inside a full AAS cycle to justify the added tax.

Product integrity is the dominant practical problem. Steroidal synthesis is more expensive than non-steroidal SARM synthesis, so substitution and mislabeling are persistent concerns. Community lab-testing reports describe bunk, underdosed, and prohormone-contaminated products, but the precise market rate should not be overstated. Third-party purity documentation and independent batch testing are the rigorous quality-control path.

Female use is not a positive lane. Female-identified evidence is sparse, the compound is androgenic, and the virilization profile is too high-tax to justify protocol recommendations. For women, this article should be read as an avoid/harm-reduction page, not as a micro-dose guide.

The overall community consensus is bullish but bounded. Experienced users often report fast strength onset and a dry/hard look, yet the same corpus also contains skepticism that YK-11 changed top-level bodybuilding or delivers much in isolation inside a heavy stack. The fair conclusion is not that YK-11 is fake; it is that the visible effect is real for some advanced users, modest in magnitude, hard to source cleanly, and expensive in monitoring/PCT burden.

Risks & Monitoring

Hippocampal neurotoxicity (clinical evidence, rodent). This is the most important and most recently surfaced safety signal.

In rats given 0.35 g/kg YK-11 over 5 weeks (Dahleh 2023, 2024), the hippocampus showed oxidative stress, mitochondrial dysfunction, elevated pro-inflammatory IL-1β and IL-6, reduced anti-inflammatory IL-10, downregulated BDNF/TrkB/CREB signaling, and increased p38 MAPK activity triggering Bax/Bcl-2/cleaved caspase-3 apoptotic cascade. Aversive memory consolidation was impaired. Exercise as a co-intervention partially offset IL-6 and IL-10 changes and Bcl-2/caspase-3 alterations, but did not rescue the BDNF downregulation or the major apoptotic signaling. PBPK modeling confirmed brain permeability — YK-11 is not peripherally restricted. Community reports of mood disturbance, motivation dips, and cognitive fog during cycles align with this finding, though without human bloodwork or imaging to confirm a direct link.

HPTA suppression. Confirmed across multiple community first-person bloodwork reports: LH and FSH drop substantially even at moderate doses, mid-cycle libido decline is common, and recovery without full SERM PCT is poor. Pre-cycle baseline matters — one logged user started with total T 450 ng/dL (lower than his stated natural 600) and ran 8 weeks at 10 mg before PCT. The suppression mechanism is straightforward: AR activation triggers negative feedback through the hypothalamic-pituitary-gonadal axis. Treat YK-11 like a DHT-derived oral steroid for restart purposes, not like a non-steroidal SARM.

Tendon and joint stress. Reported across multiple batches including one corpus-documented complete pec tear during a YK-11 cycle, elbow tendon pain beginning week 4 in an 8-week solo log, and broader community discussion of joint stiffness incompatible with powerlifting-style heavy training. The mechanism is likely connective tissue lagging behind rapid strength gain — a common feature of fast-acting anabolic compounds. Aggressive strength training while on cycle specifically flagged by experienced users as a risk amplifier.

Hair shedding and frontal hairline recession. Consistent with the DHT-derived structure. Corpus evidence specifically notes 'more hair shedding on YK 11' than during baseline SARM use. Users with male pattern hair loss susceptibility should treat frontal hairline recession as a likely irreversible effect.

Lipid changes. HDL drop and LDL rise are reported as common community findings, consistent with the oral steroidal route. A community cycle guide flags lipid monitoring explicitly. Magnitude varies; mid-cycle lipid panels at week 4-6 are the standard community recommendation.

Hepatic. The structural argument for YK-11 not being significantly hepatotoxic is that the compound has a methyl ester but lacks the 17α-alkylation that drives the classic oral-steroid liver burden. Most community first-person bloodwork shows modest or no ALT/AST elevation at standard doses. One corpus-documented practitioner ran 30 mg/day for 7 weeks alongside Anadrol and reported 'liver enzymes didn't budge much.' This is reassuring but not definitive — no large-N data exist and stacking with other hepatotoxic compounds remains a real concern.

Acne, skin dryness, mood disturbance. Acne (shoulders, rear delts, mid back) is the most common visible side effect, mild in most cases. Skin dryness reverses in most users post-cycle but persisted in one anabolic-community user even after stopping. Mood swings, motivation dips, and life-stress sensitivity have been logged — consistent with the BDNF findings.

Dose-related severity escalation. At 5 mg/day, most users report a clean experience with modest effect. At 10 mg/day, side-effect frequency increases but remains manageable in experienced users. At 20-30 mg/day, side effects become the dominant feature — tendon pain, severe pumps, cardio strain (one user at 50 mg/day reported the YK-11 displaced his other AAS at AR and dropped his strength and vascularity). The dose-response is steep above 15 mg/day.

For Women

Monitoring Panels

Avoid With

Protocols By Goal

Lean mass / bulking. 10 mg/day BID split for 8 weeks, eating 300-500 calories above maintenance with 2 g protein per lb body weight target.

Stack with RAD-140 25 mg/day and cardarine 20 mg/day for synergistic recomp signal, N2Guard throughout, full Clomid PCT weeks 9-12. Realistic outcome: 3-6 lb lean tissue with visibly tighter look at moderate to lower body fat (below 18%). Above 22% body fat, prioritize fat loss before introducing YK-11 — its myostatin axis effect is wasted on someone who cannot yet see the muscle.

Recomp. 10 mg/day BID + ostarine 25-50 mg/day (titrated up after 2 weeks) + cardarine 20 mg/day + N2Guard for 12 weeks. The triad covers anabolic signal (ostarine), endurance/lipid support (cardarine), and the myostatin-axis push (YK-11). Best for users at 15-20% body fat targeting visible composition shift without scale weight goals.

Cutting / hardening finisher. 10 mg/day solo or 10 mg + cardarine 20 mg, last 6-8 weeks of a cutting phase. Caloric maintenance or slight deficit. The goal is dryness and detail at low body fat (under 12%), not size — match the protocol to that physiology endpoint. One documented SARM community moderator cutting log ran solo YK-11 10 mg/day for 8 weeks with a 3-day pre-cycle fast to reset hunger signaling.

Plateau breaking in advanced lifters. Add YK-11 10 mg/day for 6-8 weeks to an existing test/AAS cruise to push past late-cycle strength stalls. Stack carefully — YK-11 is a DHT-class compound, so doubling down on Masteron or Anavar in the same cycle adds androgenic load without adding new mechanism. Pair with a less DHT-loaded base instead.

Bone health / connective tissue (theoretical). The 2025 Wang BMSC paper suggests a real bone signal in rodents, but no human protocol exists. Users interested in connective tissue prefer BPC-157, TB-500, or MK-677 — all of which have stronger community evidence for tendon/ligament effect. YK-11 is not the right tool for joint healing despite the bone study.

Dosing Details

Standard oral protocol. 10 mg/day is the community canonical dose. Split BID — 5 mg morning and 5 mg 6-8 hours later — based on a community-estimated 6-12 hour half-life.

Some users run once-daily and report similar results, so the BID structure is preference-driven, not validated. Cycle length 6-8 weeks oral, with a small minority extending to 12 weeks under closer bloodwork monitoring.

Beginner / cautious dose. 5 mg/day for the first 1-2 weeks to assess individual response, then titrate to 10 mg/day if no significant side effects. Pair with N2Guard or DGA Organ Support from day one. This is the dose pattern most consistently described by experienced community moderators across SARM and bodybuilding discussions.

Aggressive protocols. A pyramid pattern documented in public protocol guides goes 10 mg/day weeks 1-2, 15 mg/day weeks 3-4, 20 mg/day weeks 5-6, optional 30 mg/day weeks 7-8. The 30 mg/day endpoint is the absolute community ceiling for oral and is rarely run beyond a single cycle. Side-effect frequency rises sharply above 15 mg/day — tendon stress, lipid shifts, and mood disturbance all become more likely.

Injectable protocol. Some community reports describe YK-11 as a propylene glycol-based injectable suspension, with MCT incompatibility creating product-integrity concerns. Reported injectable protocol: 4-6 weeks MAXIMUM duration, 5-10 mg/day for beginners, 10-20 mg/day intermediate, 20+ mg/day advanced ceiling. The rationale for injectable: community claims oral bioavailability is poor (one practitioner described it as 'absolute garbage'). The injectable bypass means dose-equivalence shifts and side effects may concentrate — treat injectable as advanced-only territory.

Sublingual administration. Some users hold the oral liquid suspension under the tongue rather than swallowing, citing better absorption. Reasonable inference from the poor oral bioavailability framing, but unvalidated.

Standard stack scaffold. The most-cited template across public protocol discussions: YK-11 10 mg/day split + RAD-140 25 mg/day OR ostarine 25-50 mg/day + cardarine (GW-501516) 20 mg/day + N2Guard, 12 weeks, followed by Clomid 50/25/25/25 or nolvadex 40/20/20/20 PCT with cardarine continued 20 mg/day through PCT for cortisol management.

Cycle position. YK-11 is most commonly added in the back half of an existing SARM or AAS cycle as a hardening finisher, rather than as the cycle's foundation. Some advanced users deploy YK-11 during cruise or PCT specifically to manage myostatin elevation that follows AAS discontinuation — a fringe protocol with anecdotal support but no clinical basis.

Discontinuation rules. Stop immediately if tendon pain develops in week 1-3 (worsens with continued use). Stop if ALT or AST exceed 3x upper limit of normal at midcycle. Stop if mood disturbance progresses to interfere with daily function. Stop if HDL drops below 30 mg/dL.

Stacks & Alternatives

Most-cited co-stack across public protocol discussions. RAD-140 25 mg/day + YK-11 10 mg/day split BID + cardarine. RAD-140 provides strength + AR-driven anabolic signal; YK-11 adds the myostatin-axis push and hardening. Used together for bulking or aggressive recomp.

20 mg/day, continued through PCT. Cardarine handles endurance, lipid management, and cortisol suppression in PCT — addresses the lipid concerns YK-11 raises. Near-universal adjunct in community protocols.

25-50 mg/day for recomp. Mild AR partial agonist, low suppression, good for the cutting/recomp lane where YK-11's strength comes from hardening rather than mass. Community-reported for users who don't want the higher suppression of RAD-140.

20-25 mg/day for sleep, recovery, joint comfort during a YK-11 cycle. The GH-pulse signal pairs with YK-11's myostatin-axis effect for synergistic muscle/recovery — though MK-677 fluid retention can mute YK-11's dry phenotype, so dose conservatively if dryness is the goal.

100-150 mg/week testosterone enanthate or cypionate. The most-recommended structural choice for users who want to skip the SERM PCT cycle. YK-11 on a test base behaves like an oral hardening adjunct similar to Masteron, with steady AR floor maintained by the test.

Liver/kidney/cardiovascular support stack throughout cycle and PCT. Defense-in-depth against the oral steroidal route's hepatic and lipid burden.

500 mg/day for hepatic protection, especially when stacking YK-11 with other orals. Standard community liver support pairing with any oral compound.

50 mg/day split for cutting/recomp protocols. The dryness-stacking lane — YK-11 + S4 produces a heavily hardened phenotype. Note: S4 has its own vision-disturbance side effect; not a first-choice adjunct.

Alternatives

Stack Cost

Practical Setup

Product Integrity. YK-11 is one of the most-mislabeled compounds on the unregulated SARM shelf because steroidal synthesis is expensive enough that sellers have economic motive to substitute.

Insist on third-party COA testing for every batch; seller-provided testing is not enough for a compound where bunk, underdosed, and prohormone-contaminated products have been reported. Avoid making a quality decision from community reputation alone because reputation lists drift and batch quality can change.

Form factors. Oral liquid suspensions and capsules are the common reported forms. Injectable suspensions are discussed in advanced circles but add sterility, preparation, and uneven-quality risks; they should not be treated as a casual route.

Storage. Storage is simple compared with fragile peptides, but users should follow the product-specific stability instructions and treat degraded or contaminated preparations as a real risk.

Administration. Oral and sublingual use are both reported, but absorption claims are not clinically validated. Twice-daily splitting is the most-cited pattern; some users report once-daily use without an obvious effect penalty.

Pre-cycle workup. Full panel: CBC, CMP including liver and kidneys, lipid panel, total + free testosterone, LH, FSH, sensitive estradiol, SHBG, blood pressure baseline. The cycle costs of skipping baseline labs accumulate — you cannot identify post-cycle abnormalities without a pre-cycle anchor.

Mid-cycle workup. Week 4-6: ALT, AST, lipid panel. The ALT measurement is the primary safety stop-rule — if it exceeds 3x upper limit of normal, discontinue. If lipids deteriorate severely (HDL below 30 mg/dL, non-HDL above 160 mg/dL), reassess cycle.

Post-cycle workup. 4-8 weeks after PCT ends: total + free T, LH, FSH, sensitive E2, repeat lipid panel and ALT. If HPTA has not recovered to baseline by week 8 post-cycle, refer to endocrinology before considering another cycle.

Signs to pivot or stop. Tendon pain in any joint (worsening = stop). ALT/AST elevation 3x ULN or higher. HDL crashing below 30 mg/dL midcycle. Mood disturbance interfering with daily function. Hair shedding rate noticeably above baseline if hairline preservation is a goal. Severe persistent dryness or vascularity loss (the AR-displacement signal).

Drug interactions. YK-11 may compete at AR with testosterone, DHT, and other AAS at high doses — the practical implication is that adding YK-11 to a heavy AAS stack at 50+ mg/day risks paradoxical displacement effects. With 5α-reductase substrates (testosterone, nandrolone), the Dahleh in silico finding that YK-11 inhibits 5αR2 means downstream DHT production may be partially suppressed — relevant for users relying on DHT for libido or for users prone to hair-loss who hope 5α-reductase inhibition protects the hairline (it does not, because YK-11 is itself androgenic at the AR).

Cost framing. Raw compound cost is usually lower than the true cycle cost. PCT, liver support, cardiovascular monitoring, and bloodwork make the practical cost materially higher, and purity verification matters more than bargain pricing.

Documentation. Photo log start/midcycle/end. Bloodwork at the three checkpoints. Subjective notes on mood, sleep, libido, tendon stress, training response. Without documentation, the wide interindividual variation in this compound makes it impossible to learn from your own cycles.

Mechanism Deep Dive

Primary mechanism: AR partial agonism with selective transactivation. YK-11 binds the androgen receptor in muscle and bone tissue but activates it differently than DHT or non-steroidal SARMs.

Kanno's 2022 paper in Experimental Cell Research demonstrated differential DNA-binding and cofactor recruitment in MDA-MB-453 breast cancer cells — YK-11 produces gene-selective transactivation rather than the broad AR-target gene activation of full agonists. This is the structural basis for calling YK-11 a SARM despite the steroidal backbone: the receptor activates, but the downstream gene expression pattern is restricted.

Follistatin induction — the distinguishing pathway. Kanno's 2013 paper in Biological and Pharmaceutical Bulletin established the mechanism that drives community interest. In C2C12 mouse myoblast cells, YK-11 treatment induced follistatin (Fst) expression that DHT did not. The myogenic regulatory factors MyoD, Myf5, and myogenin were activated more by YK-11 than by DHT. Crucially, anti-follistatin antibody fully reversed the YK-11-induced myogenic differentiation — confirming that the anabolic signal flows through follistatin rather than direct AR transcription alone. Follistatin is the body's endogenous antagonist of myostatin, so the inferred chain is: YK-11 → AR activation → follistatin induction → myostatin neutralization → muscle growth signal. The Kanno findings replicate across the Toho University group's later papers (cited in Biological & Pharmaceutical Bulletin 36(9), 1460-1465, 2013).

Caveats on follistatin induction. The follistatin elevation has been shown in only two studies (Kanno 2013 and Kanno 2022) using cell models and animal models. The certainty of the effect in humans at community doses is inferred, not measured. Some corpus voices note that 'YK-11 increases follistatin levels only in animal models' — the human translation is unverified.

Bone effects via BMP2/Smad pathway. Wang et al. 2025 (Journal of Molecular Endocrinology 74(2)) showed YK-11 promotes osteogenic differentiation of bone marrow-derived mesenchymal stem cells at 0.25-4 μM in vitro, with the effect intensifying with concentration. 2 μM specifically increased BMSC proliferation. In vivo, YK-11-equipped hydrogel at 0.5 and 1 mg/mL promoted cranial defect repair in Sprague-Dawley rats. AR antagonism abolished both effects. The proposed downstream effector is BMP2 (bone morphogenetic protein 2) / Smad signaling — a well-established osteogenic pathway. The One editorial-grade mention of Protein Kinase B (PKB / Akt) is plausible downstream from AR activation but less directly supported than the BMP2/Smad findings.

5α-reductase type 2 inhibition. Dahleh 2024 in silico docking analysis revealed YK-11 competes at the inhibitory domain of 5α-reductase type 2 (5αR2). The practical implication: YK-11 may interfere with DHT synthesis from testosterone in tissues where 5αR2 is the dominant isoform — prostate, hair follicles, some skin. This complicates the assumption that DHT-derived effects of YK-11 mimic standard DHT biology, and may interact with finasteride/dutasteride users in unpredictable ways.

Hippocampal mechanism — the neurotoxicity story. Dahleh et al. (2023 in The Journal of Steroid Biochemistry and Molecular Biology Vol 233, 106364; 2024 in Chemico-Biological Interactions Vol 394, 110971) demonstrated that anabolic-dose YK-11 in rats produces measurable hippocampal damage through multiple intersecting pathways: - Blood-brain barrier permeability. PBPK modeling demonstrated remarkable brain permeability; YK-11 reaches hippocampal tissue at functionally significant concentrations. - High AR binding in hippocampus. Molecular docking confirmed strong binding affinity to hippocampal AR. - Oxidative stress and mitochondrial dysfunction. Direct mechanism of neuronal damage; comparable to traditional AAS at equivalent doses. - Pro-inflammatory cytokine elevation. IL-1β and IL-6 increased; anti-inflammatory IL-10 decreased. - BDNF/TrkB/CREB downregulation. The neurotrophic signaling pathway underpinning memory formation is suppressed. Exercise did not rescue this. - Apoptotic cascade activation. p38 MAPK → Bax/Bcl-2/cleaved caspase-3 — programmed neuronal cell death signaling. Exercise partially mitigated Bcl-2 and caspase-3 alterations but did not eliminate the apoptotic signal. - Memory consolidation impairment. Aversive memory consolidation specifically affected in the behavioral readout.

Receptor selectivity. YK-11 reportedly has little or no affinity for the glucocorticoid receptor and inhibits both mineralocorticoid and estrogen receptors based on single-study cell data. The selectivity findings come from a single concentration in a single in vitro context and may not translate to bodybuilding-dose exposures.

FKBP51 elevation. YK-11 increases FKBP51 levels similarly to DHT compounds. FKBP51 is a glucocorticoid receptor co-chaperone involved in cell survival pathways. Healthy users have no documented harm from FKBP51 elevation, but in patients with active cancer the protein's role in cell survival creates a theoretical concern. Community pharmacology framing has codified this as a contraindication for active cancer patients.

Metabolism and elimination. Piper 2018 (Drug Testing and Analysis 10(11-12), 1646-1656) used deuterated YK-11 in vivo and identified 14 urinary metabolites comprising unconjugated, glucuronidated, and sulfoconjugated forms. No intact YK-11 was observed in elimination study urine. Unconjugated metabolites cleared within 24 hours; glucuronidated and sulfated metabolites were detectable for over 48 hours. The two most promising glucuronidated metabolites (5β-19-nor-pregnane-3α,17β,20-triol and 5β-19-nor-pregnane-3α,17β-diol-20-one) were synthesized in-house and confirmed by NMR for use in anti-doping detection panels. The labile orthoester-derived D-ring moiety is responsible for the rapid and extensive metabolic conversion.

What is NOT established mechanistically. Half-life in humans is inferred from felt-effect onset, not measured. Oral bioavailability is community-described as poor without published numbers. Long-term effects on the HPG axis, lipid profile, cardiovascular system, and cognition beyond the rodent BDNF findings are entirely unstudied in humans. The full pharmacokinetic-pharmacodynamic profile remains a community estimate.

Evidence Index