LGD-4033 (Ligandrol, VK5211) holds a distinctive position in the SARM research landscape: while RAD-140 may be more potent and selective, LGD-4033 has accumulated the most robust human clinical trial dataset of any SARM — including a published Phase II trial in hip fracture patients. This clinical depth makes it the most well-characterized SARM from a human pharmacology standpoint.
What Is LGD-4033?
LGD-4033 is a non-steroidal SARM developed by Ligand Pharmaceuticals (later acquired by Viking Therapeutics as VK5211). It selectively binds the androgen receptor with high affinity and produces tissue-selective anabolic effects — primarily in skeletal muscle and bone — with significantly reduced androgenic activity in prostate and other androgenic tissues. It has completed Phase I safety studies and Phase II efficacy trials in multiple populations.
Mechanism of Action
Selective AR Binding: LGD-4033 binds the androgen receptor with Kd ~1nM — comparable to testosterone — but induces a distinct receptor conformation that activates anabolic gene programs in muscle and bone while producing minimal androgenic transcriptional activity in prostate tissue.
Anabolic Gene Activation: In skeletal muscle, AR-LGD-4033 activates genes involved in myosin heavy chain synthesis, IGF-1 expression, satellite cell activation, and nitrogen retention — the molecular underpinnings of muscle hypertrophy.
Bone Mineral Density: LGD-4033 activates AR in osteoblasts, stimulating bone formation and increasing bone mineral density in animal models — relevant to osteoporosis and fracture healing research.
HPG Axis Suppression: Like all AR agonists, LGD-4033 suppresses the hypothalamic-pituitary-gonadal axis through negative feedback, reducing endogenous LH, FSH, and testosterone production in a dose-dependent manner. This is well-documented in human trials and a primary consideration in research protocol design.
Human Clinical Research
Phase I (Healthy Volunteers)
A landmark published Phase I trial in 76 healthy men demonstrated LGD-4033: dose-dependently increased lean body mass (1.21 kg at 1mg/day over 21 days), reduced total and free testosterone (dose-dependent, reversible), reduced sex hormone-binding globulin (SHBG), and was well-tolerated with no drug-related serious adverse events. This remains one of the most cited human SARM studies in the literature.
Phase II (Hip Fracture — VK5211)
Viking Therapeutics conducted Phase II trials with VK5211 (LGD-4033) in elderly hip fracture patients, demonstrating significant improvements in lean body mass and physical function versus placebo — validating the anabolic activity seen in Phase I in a clinically relevant population with muscle wasting.
LGD-4033 vs. RAD-140 vs. Ostarine
| Feature | LGD-4033 | RAD-140 | Ostarine (MK-2866) |
|---|---|---|---|
| Potency | High | Highest (~90:1) | Moderate |
| Human trial data | Most extensive | Phase I + II (oncology) | Most Phase III data |
| HPG suppression | Moderate-significant | Significant | Mild-moderate |
| Best research use | Muscle wasting, body comp | Potency, neuroprotection | Bone density, mild anabolic |
Conclusion
LGD-4033’s combination of high anabolic potency, tissue selectivity, and — most importantly — the deepest human clinical dataset of any SARM makes it the reference compound for human SARM pharmacology research. For researchers studying androgen receptor biology, muscle wasting, or body composition in human models, LGD-4033 is an essential research tool. Combat Research provides research-grade LGD-4033 for qualified research applications.
Shop LGD-4033 at Combat Research
Related Research Articles
For research purposes only. Not for human therapeutic use.
