SR-9009 (Stenabolic) vs YK-11

Mechanism

SR-9009 is a synthetic agonist of REV-ERBa and REV-ERBb, nuclear receptors that form the repressive limb of the circadian clock and regulate metabolic gene expression. REV-ERB activation represses BMAL1/CLOCK transcription, modulating circadian rhythm. In skeletal muscle, SR-9009 increases mitochondrial count and oxidative capacity by upregulating mitochondrial biogenesis genes. It enhances fatty acid and glucose oxidation, increases exercise endurance, and reduces lipogenesis in the liver. SR-9009 also reduces inflammatory gene expression via NF-kB pathway suppression. Recent research has identified significant REV-ERB-independent effects, suggesting the mechanism is more complex than initially characterized.

Standard Dosing

Research indicates 20-30 mg daily orally, split into 3-4 doses due to very short half-life (~4 hours). Some users prefer sublingual administration for improved bioavailability.

Timing

Split into 3-4 doses throughout the day due to ~4-hour half-life. Example: 7am, 11am, 3pm, 7pm. Avoid late-night dosing as REV-ERB modulation may affect circadian rhythm and sleep.

Cycle Duration

8-12 week cycles. No HPG suppression. Cycling recommended due to limited long-term data.

Side Effects

• Insomnia or sleep disruption (circadian clock modulation)
• Anxiety or wakefulness
• Headache
• Nausea
• Potential circadian rhythm disruption with chronic use

Contraindications

• Circadian rhythm disorders or shift work (may exacerbate disruption)
• Pregnancy and breastfeeding
• Individuals under 21
• Severe insomnia

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Mechanism

YK-11 is a synthetic steroidal compound classified as a gene-selective partial agonist of the androgen receptor. Uniquely among SARMs, YK-11 does not induce the N/C terminal interaction of the AR required for full transcriptional activation, instead selectively activating a subset of AR-dependent genes. Its primary distinguishing mechanism is potent induction of follistatin expression, which directly antagonizes myostatin — a key negative regulator of skeletal muscle mass. This dual action (partial AR agonism + myostatin inhibition via follistatin) theoretically provides anabolic stimulus beyond what full AR agonists alone can achieve.

Standard Dosing

Research indicates 5-15 mg daily orally for 6-8 weeks. No human clinical trials exist — all dosing data is anecdotal.

Timing

Split into 2 daily doses (morning and evening) due to presumed short half-life (~6-10 hours based on structural analysis). Consistent timing essential.

Cycle Duration

6-8 week cycles maximum. PCT strongly recommended. Avoid extended use due to unknown long-term safety profile.

Side Effects

• Testosterone suppression (expected — steroidal compound)
• Hepatotoxicity (17-alpha-alkylated structure implies liver toxicity risk)
• Joint pain and tendon issues (anecdotal — possibly from DHT-like drying effects)
• Hair loss (steroidal androgenic effects)
• Aggression
• Unknown long-term effects (no human studies)

Contraindications

• Pre-existing liver disease
• Androgen-sensitive cancers
• Cardiovascular disease
• Pregnancy and breastfeeding
• Individuals under 21
• Anyone unwilling to accept research chemical risk with zero human clinical data

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