LGD-4033 (Ligandrol) vs Ostarine (MK-2866 / Enobosarm)

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

Ostarine (enobosarm/GTx-024) is a nonsteroidal selective androgen receptor modulator that binds the androgen receptor with high affinity, inducing a conformational change that recruits coactivator proteins preferentially in muscle and bone tissue over prostate and seminal vesicles. This tissue selectivity arises from differential AR cofactor recruitment and 5-alpha reductase metabolism. Ostarine promotes lean body mass by activating AR-mediated transcription of anabolic genes (MYC, IGF-1) in myocytes while minimizing androgenic effects in reproductive tissues. It has demonstrated dose-dependent increases in lean mass in Phase 2 trials.

Standard Dosing

Research indicates 10-25 mg daily orally for 8-12 weeks. Phase 2 clinical trials used 1-3 mg/day with significant lean mass gains.

Timing

Once daily, morning or evening. Consistent timing. Half-life approximately 24 hours. No food timing requirements.

Cycle Duration

8-12 week cycles. PCT may be required depending on suppression level and cycle length.

Side Effects

• Testosterone suppression (dose and duration dependent — mild to moderate)
• Elevated liver enzymes (hepatotoxicity reports)
• HDL suppression
• Headache
• Nausea
• Back pain
• Joint dryness (from estradiol reduction secondary to testosterone suppression)

Contraindications

• Androgen-sensitive cancers (prostate, breast)
• Pre-existing liver disease
• Pregnancy and breastfeeding
• Individuals under 21 (potential endocrine development disruption)
• Athletes subject to WADA testing (prohibited substance)

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