MK-677 (Ibutamoren) vs YK-11

Mechanism

MK-677 (ibutamoren) is an orally active, non-peptide growth hormone secretagogue that mimics ghrelin by binding the ghrelin receptor (GHSR1a) in the hypothalamus and pituitary. This triggers pulsatile growth hormone release via the same physiological mechanism as endogenous ghrelin, preserving the natural episodic GH secretion pattern. MK-677 increases GH, IGF-1, and IGFBP-3 levels to those observed in young adults without affecting cortisol levels. It also stimulates appetite through ghrelin receptor activation in the hypothalamus. Unlike exogenous GH injection, MK-677 maintains the pulsatile GH pattern and stimulates all five GH isoforms.

Standard Dosing

Research indicates 10-25 mg daily orally. Clinical trials used 25 mg/day. 10-15 mg may provide GH elevation with fewer side effects.

Timing

Take 30-60 minutes before bedtime. This timing leverages the natural nocturnal GH pulse, maximizes sleep quality benefits, and minimizes daytime appetite increase. Half-life ~24 hours ensures once-daily dosing is sufficient.

Cycle Duration

Can be used continuously for months to years — no cycling required as it works through physiological GH release mechanisms. Clinical trials ran for up to 2 years. Reassess IGF-1 and metabolic markers every 3-6 months.

Side Effects

• Increased appetite (ghrelin mimetic — significant and persistent)
• Water retention and bloating (GH-mediated)
• Numbness and tingling (carpal tunnel-like symptoms)
• Elevated fasting blood glucose and insulin resistance
• Lethargy and increased sleep depth
• Vivid dreams
• Joint pain (less common than exogenous GH)

Contraindications

• Active malignancy (GH/IGF-1 promotes cell proliferation)
• Diabetes mellitus (impairs glucose tolerance — use with extreme caution)
• Active diabetic retinopathy
• History of pituitary tumors
• Congestive heart failure (fluid retention)

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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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