LGD-4033 (Ligandrol) vs MK-677 (Ibutamoren)

Mechanism

LGD-4033 is a potent nonsteroidal selective androgen receptor modulator with high AR binding affinity (Ki of approximately 1 nM). It demonstrates strong anabolic activity in muscle and bone with significantly reduced androgenic activity in prostate tissue, achieving an anabolic-to-androgenic ratio of approximately 10:1. LGD-4033 activates the AR with full agonist efficacy in muscle, upregulating the PI3K/Akt/mTOR pathway for protein synthesis and satellite cell recruitment. It produces dose-dependent suppression of SHBG, total testosterone, LH, and FSH, indicating significant HPG axis suppression even at low doses.

Standard Dosing

Research indicates 5-10 mg daily orally for 8-12 weeks. Phase 1 data showed significant lean mass gains at 1 mg/day.

Timing

Once daily, consistent timing. Half-life approximately 24-36 hours. No food timing requirements.

Cycle Duration

8-12 week cycles maximum. PCT strongly recommended after all but the shortest/lowest-dose cycles.

Side Effects

• Significant testosterone suppression (dose-dependent; occurs even at 1 mg/day)
• Suppressed SHBG, LH, and FSH
• Elevated liver enzymes / hepatotoxicity (case reports of cholestatic liver injury)
• HDL cholesterol suppression
• Headache
• Fatigue (late-cycle, from suppression)
• Water retention

Contraindications

• Androgen-sensitive cancers
• Pre-existing liver disease or elevated liver enzymes
• Pregnancy and breastfeeding
• Individuals under 21
• Athletes subject to WADA/anti-doping testing

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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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