LGD-4033 (Ligandrol) Research Guide: Pharmacokinetics, Uses & 2026 Clinical Data

LGD-4033 (Ligandrol) is an investigational, non-steroidal Selective Androgen Receptor Modulator (SARM) developed to treat muscle wasting and osteoporosis. It selectively binds androgen receptors in skeletal muscle and bone, increasing lean body mass without significant androgenic effects in non-target tissues. LGD-4033 is not FDA-approved and is strictly not for human consumption — it is available for Research Use Only (RUO) by qualified laboratory investigators.

Originally developed by Ligand Pharmaceuticals and currently under investigation by Viking Therapeutics, LGD-4033 is the subject of completed Phase I and Phase II clinical trials. As of 2026, it remains an Investigational New Drug (IND) available exclusively for Research Use Only (RUO) applications by qualified laboratory investigators. Its developmental code VK5211 identifies it within Viking’s clinical pipeline.

As of 2026, the research landscape surrounding LGD-4033 has expanded significantly. While its foundational Phase I and Phase II data established its potency in increasing lean body mass, contemporary 2026 research has pivoted toward its role as an adjunctive agent. Specifically, independent investigators are now evaluating its potential to mitigate the unintended lean mass loss associated with long-term GLP-1 receptor agonist therapy. This guide provides a comprehensive technical overview of LGD-4033, including its chemical properties, molecular mechanism, pharmacokinetic profile, and the most recent regulatory developments affecting its status in laboratory environments.

What Is LGD-4033? Defining the VK5211 SARM

LGD-4033 is a high-affinity, orally bioavailable, non-steroidal Selective Androgen Receptor Modulator. Unlike traditional testosterone derivatives, which possess a four-ring steroid nucleus, LGD-4033 belongs to a class of aryl propionamides and benzonitril-based ligands. This structural divergence is critical; it allows the molecule to interact with the androgen receptor (AR) without being a substrate for 5-alpha reductase or aromatase. Consequently, research models do not observe the conversion into dihydrotestosterone (DHT) or estrogenic metabolites, which are often the drivers of side effects in steroidal compounds.

In clinical research, LGD-4033 is often referred to by its developmental name, VK5211. It was designed to demonstrate high tissue selectivity, exhibiting potent anabolic activity in musculoskeletal tissues while maintaining a significantly reduced effect on the prostate and sebaceous glands. This selectivity is the hallmark of the SARM class, aiming to achieve the therapeutic benefits of androgens without the systemic virilization or androgenic hypertrophy associated with multi-organ AR activation.

Chemical Structure & Pyrrolidinyl-Benzonitrile Core

The chemical identity of LGD-4033 is defined by its IUPAC designation: 4-[(2R)-2-[(1R)-2,2,2-trifluoro-1-hydroxyethyl]pyrrolidin-1-yl]-2-(trifluoromethyl)benzonitrile. The molecule is characterized by a pyrrolidinyl-benzonitrile core, which is central to its high binding affinity. The inclusion of trifluoromethyl groups at specific positions on the benzonitrile ring enhances the molecule’s electronegativity and metabolic stability, allowing it to bypass first-pass hepatic metabolism more effectively than previous generations of SARMs.

Technical specifications for LGD-4033 include:

• Molecular Formula: C14H12F6N2O
• Molecular Weight: 338.25 g/mol
• CAS Number: 1165910-22-4
• Binding Affinity (Ki): Approximately 1 nM

The pyrrolidin-1-yl moiety, combined with the trifluoro-hydroxyethyl side chain, creates a unique spatial orientation that fits precisely into the ligand-binding domain (LBD) of the androgen receptor. This precision is what dictates its high potency, even at sub-milligram concentrations in research subjects.

Mechanism of Action: Tissue Selectivity and Androgen Receptor Binding

The mechanism of action for LGD-4033 is rooted in its role as a partial-to-full agonist of the Androgen Receptor (AR). Upon oral administration in research models, LGD-4033 crosses the cell membrane and binds to the AR in the cytoplasm. This binding triggers a conformational change in the receptor, leading to its translocation into the nucleus. Once inside the nucleus, the AR-LGD-4033 complex binds to specific DNA sequences known as androgen response elements (AREs), initiating the transcription of genes involved in protein synthesis and osteoblastic activity.

The “selectivity” of LGD-4033 is theorized to result from its unique ability to recruit different co-activator or co-repressor proteins depending on the tissue type. In skeletal muscle and bone tissue, the LGD-4033-bound AR favors the recruitment of co-activators that promote anabolic gene expression. Conversely, in androgen-sensitive tissues like the prostate, the complex may adopt a conformation that limits the recruitment of these same co-activators, or potentially recruits co-repressors, thereby minimizing hypertrophy. This tissue-specific gene expression is the primary reason why LGD-4033 is researched for its ability to increase lean body mass without the significant increase in Prostate-Specific Antigen (PSA) levels typically seen with testosterone.

Pharmacokinetics of LGD-4033 in Clinical Research

Understanding the pharmacokinetics (PK) of LGD-4033 is essential for designing accurate in vivo studies. Clinical data indicates that LGD-4033 exhibits a highly predictable PK profile, characterized by high oral bioavailability and a prolonged terminal half-life.

Half-Life, Absorption, and Elimination Rates

LGD-4033 demonstrates an oral bioavailability estimated to be greater than 70%. Following administration, peak plasma concentrations (Cmax) are typically reached within 4 to 8 hours. One of the most significant findings in Phase I human clinical trials (such as the Bhasin et al. study) was the compound’s half-life, which was measured at 24 to 36 hours. This extended duration of action allows for stable plasma levels with a once-daily administration protocol in research settings.

The metabolism of LGD-4033 primarily involves hepatic pathways, though it is not a 17-alpha-alkylated compound, which distinguishes it from many oral anabolic steroids. Elimination is primarily through urinary and fecal routes. In research subjects, LGD-4033 displays linear pharmacokinetics, meaning that increases in dosage result in proportional increases in plasma concentration and systemic exposure (Area Under the Curve, or AUC). This linearity simplifies the calculation of exposure-response relationships in clinical trials.

Clinical Trial History and Emerging 2026 Research Trends

The clinical progression of LGD-4033 is one of the most documented among all Selective Androgen Receptor Modulators. The landmark study, published by Bhasin et al. in the Journals of Gerontology, involved a 21-day, randomized, placebo-controlled, dose-escalation trial. The study utilized doses of 0.1mg, 0.3mg, and 1.0mg in healthy young men.

Lean Body Mass and Bone Density Studies

The Bhasin study provided the first definitive proof of LGD-4033’s anabolic potential. In the 1.0mg group, research subjects experienced an average increase in lean body mass of 1.21 kg (+2.67 lbs) over the 21-day period. This gain was achieved without any specific exercise intervention, highlighting the compound’s potent nutrient-partitioning effects. Furthermore, the study noted dose-dependent increases in leg press strength and improvements in stair-climbing power, suggesting functional benefits alongside structural changes.

In terms of bone density, preclinical models have shown that LGD-4033 increases bone mineral density (BMD) by stimulating osteoblastic activity and reducing bone resorption. These findings led to the initiation of trials focused on hip fracture recovery (VK5211), where the goal is to prevent the rapid muscle atrophy and bone loss that typically follows orthopedic surgery in elderly populations.

Phase II Hip Fracture Trial: NCT02578095

Beyond the foundational Bhasin Phase I trial, LGD-4033 has been investigated in a Phase II clinical study (NCT02578095) examining its efficacy in older adults recovering from hip fracture surgery — a population prone to severe muscle and bone density loss. The trial evaluated whether LGD-4033 could improve lean body mass recovery, physical function, and bone mineral density (BMD) in post-operative hip fracture patients. This application directly underpins Viking Therapeutics’ designation of the compound as VK5211 and represents the most clinically significant use case in LGD-4033’s development history. Results confirmed lean mass gains and improved functional outcomes, supporting the compound’s anabolic potential in sarcopenic research populations.

SARM and GLP-1 Co-Therapy Research: Muscle Preservation

A significant shift in the research landscape occurred in early 2026. Data published in the February 2026 Journal of Clinical Endocrinology & Metabolism (JCEM) highlighted a critical challenge in modern metabolic medicine: the use of GLP-1 receptor agonists (such as Semaglutide and Tirzepatide) for weight loss often results in 25–40% of the total weight lost being lean muscle mass rather than adipose tissue. This “muscle-wasting” side effect can lead to sarcopenic obesity and metabolic slowing.

As a result, LGD-4033 is now being investigated as a potential adjunctive therapy to be used alongside GLP-1 agents. The 2026 research trend focuses on whether the potent anabolic signaling of LGD-4033 can “shield” muscle tissue from the catabolic effects of caloric restriction and GLP-1-mediated weight loss. Early data suggests that even low-dose LGD-4033 may preserve protein synthesis in research models undergoing rapid weight loss, potentially improving the quality of weight lost and maintaining metabolic rate. Researchers are frequently referencing the compounded semaglutide legal status when designing these multi-compound metabolic studies.

LGD-4033 vs. RAD-140 (Testolone): Comparative Analysis

Researchers often compare LGD-4033 to RAD-140 (Testolone), as both are potent SARMs but exhibit distinct pharmacological profiles. Understanding these differences is vital for selecting the appropriate ligand for specific investigational aims.

Receptor Affinity and Potency Differences

In terms of binding affinity, LGD-4033 is generally considered more potent on a milligram-for-milligram basis than RAD-140. LGD-4033 has a binding affinity (Ki) of approximately 1 nM, whereas RAD-140 (Testolone) has a Ki of approximately 7 nM. This suggests that LGD-4033 achieves androgen receptor saturation at lower concentrations. In research models, LGD-4033 is often associated with more significant intracellular water retention and rapid weight gain, while RAD-140 is noted for its neurological protective effects and “dry” lean mass accrual.

Pharmacokinetic Variances: Half-Life Comparison

The half-life represents the most significant pharmacokinetic divergence between the two compounds. While LGD-4033 has a half-life of 24–36 hours, RAD-140 has a significantly longer half-life, measured at approximately 60 hours in recent studies. This means RAD-140 takes much longer to reach a steady-state concentration and longer to clear the system following the cessation of the study. For researchers requiring rapid titration or clearance, LGD-4033 provides a more manageable profile than the long-acting RAD-140.

LGD-4033 vs. Ostarine (Enobosarm): Key Distinctions

Ostarine (Enobosarm, MK-2866) represents the most extensively clinically trialed SARM alongside LGD-4033. Key differences: LGD-4033 exhibits a higher androgen receptor binding affinity (Ki ~1nM) versus Ostarine (Ki ~4nM), resulting in greater lean body mass gains at lower doses. However, Ostarine demonstrates a more favorable testosterone suppression profile, making it preferable for research models where HPG axis preservation is a priority. Both compounds are on WADA’s S1.2 Prohibited List and are strictly RUO. Ostarine is often studied in GLP-1 muscle-preservation co-therapy protocols alongside LGD-4033 as a lower-suppression alternative.

Safety Profile and Documented Preclinical Observations

While LGD-4033 is one of the most “human-ready” SARMs in terms of clinical trial progression, it is not without physiological effects that must be monitored in a research setting. It is important to note the following: LGD-4033 is an investigational compound supplied strictly for laboratory and in vitro/in vivo research applications. It is not approved for human consumption, therapeutic use, or dietary supplementation.

Testosterone Suppression and Lipid Metabolism

Clinical trials have documented that LGD-4033 causes dose-dependent testosterone suppression. In the Phase I Bhasin study, subjects receiving 1.0mg daily experienced a significant reduction in total testosterone and Sex Hormone-Binding Globulin (SHBG). Interestingly, while total testosterone was suppressed, there were no clinically significant changes in Luteinizing Hormone (LH) or Follicle-Stimulating Hormone (FSH) in the short-term model, suggesting that the hypothalamic-pituitary-gonadal (HPG) axis remains partially functional, though suppressed.

Changes in lipid metabolism are also observed. Dose-dependent reductions in High-Density Lipoprotein (HDL) cholesterol and triglyceride levels have been recorded. These markers typically return to baseline following the cessation of the compound, but they highlight the need for cardiovascular monitoring in long-term research protocols.

Hair Shedding: Telogen Effluvium in Research Models

April 2026 UK MHRA guidance highlighted telogen effluvium — a temporary hair shedding condition — as a reported adverse observation associated with LGD-4033 administration. Telogen effluvium occurs when HPG axis suppression and androgen receptor modulation disrupt the anagen-to-telogen transition in hair follicles, causing diffuse shedding. This effect is generally reversible upon compound cessation and HPG axis recovery. Research protocols employing LGD-4033 in in-vivo models should document dermatological observations alongside standard endocrine panels.

Hepatotoxicity and Drug-Induced Liver Injury (DILI) in Research Models

While LGD-4033 is not a 17-alpha-alkylated steroid, some hepatotoxicity signals have been noted in case reports and high-dose animal models. These typically manifest as transient elevations in liver enzymes (ALT/AST). In controlled clinical trials, these elevations were generally mild and did not meet the criteria for drug-induced liver injury (DILI). However, researchers must prioritize the use of high-purity compounds to avoid contaminants that may exacerbate hepatic stress. Proper peptide reconstitution and storage (though LGD is usually handled as a liquid or powder) is essential for maintaining chemical integrity and preventing degradation products that could increase toxicity.

Clinical case series document cholestatic Drug-Induced Liver Injury (DILI) in subjects who self-administered LGD-4033 from unverified sources, presenting with markedly elevated aspartate aminotransferase (AST) and alanine aminotransferase (ALT) enzyme levels. The Bhasin et al. Phase I trial — using verified pharmaceutical-grade compound at 0.1–1.0mg doses — reported no clinically significant hepatic enzyme elevation, indicating that DILI signals in case reports may be attributable to product impurities rather than the compound itself. Institutional research protocols should include baseline and periodic hepatic function panels (AST, ALT, bilirubin) as a standard safety measure.

Post-Cycle Therapy (PCT) and Hypothalamic-Pituitary-Gonadal (HPG) Axis Recovery

LGD-4033 induces dose-dependent suppression of the hypothalamic-pituitary-gonadal (HPG) axis, reducing luteinizing hormone (LH), follicle-stimulating hormone (FSH), total testosterone, free testosterone, and sex hormone-binding globulin (SHBG). In the Bhasin et al. Phase I trial, testosterone levels recovered to baseline within 5 weeks of cessation at 1.0mg doses. In research protocols, Post-Cycle Therapy (PCT) using selective estrogen receptor modulators (SERMs) such as enclomiphene or tamoxifen may be employed to accelerate HPG axis restoration in in-vivo research models. Organ support compounds including N-acetyl cysteine (NAC) and tauroursodeoxycholic acid (TUDCA) are standard laboratory practice during extended SARM administration studies.

LGD-4033 Regulatory Status 2026: FDA and WADA

The regulatory environment for SARMs has tightened significantly in 2026, driven by an increase in mislabeled products in the consumer market. Researchers must be aware of the legal distinctions between “Research Use Only” compounds and prohibited dietary supplements.

Investigational New Drug Status

LGD-4033 remains an Investigational New Drug (IND). It has not been approved by the FDA for the treatment of any medical condition. In late 2025 and early 2026, the FDA issued several FDA Warning Letters to vendors (notably the Titan SARMs LLC enforcement action) who were mislabeling SARMs as dietary supplements or making specific health claims. These enforcement actions underscore the necessity for vendors like Loti Labs to maintain strict RUO compliance, focusing on analytical transparency through ICP-MS testing and COA availability.

A significant 2026 development: Viking Therapeutics’ Q1 2026 earnings report (May 11, 2026) confirmed that VK5211 (LGD-4033) is now “positioned for partnering” rather than active internal Phase III development, with Viking redirecting primary resources to VK2735, their GLP-1/GIP co-agonist for obesity. This does not alter LGD-4033’s IND status but signals a shift in the pharmaceutical development timeline. Independent research interest in LGD-4033 remains active, particularly in the context of GLP-1-induced lean mass preservation studies.

WADA Prohibited List and Anti-Doping Enforcement

LGD-4033 is explicitly listed on the WADA Prohibited List under Category S1.2 (Other Anabolic Agents). It is banned at all times (both in-competition and out-of-competition) for all athletes subject to the World Anti-Doping Code. Due to its long half-life and the presence of long-term metabolites, LGD-4033 has a significant detection window in urine and blood samples. Anti-doping laboratories have developed highly sensitive liquid chromatography-mass spectrometry (LC-MS) assays capable of detecting LGD-4033 metabolites weeks after the final administration in a research subject.

WADA-accredited laboratories detect LGD-4033 via LC-MS/MS analysis targeting both the parent compound and its dihydroxylated metabolites in urine — the latter extending the detection window to approximately 21 days post-administration. As of 2025–2026, over 60 Adverse Analytical Findings (AAFs) involving LGD-4033 have been recorded across powerlifting and track-and-field disciplines, making it one of the most commonly detected prohibited SARMs. USADA has issued explicit warnings regarding supplement contamination with LGD-4033, as trace amounts in unlabeled products may trigger positive anti-doping tests.

Frequently Asked Questions About LGD-4033

Is LGD-4033 FDA approved?

No. As of 2026, LGD-4033 (Ligandrol) remains classified as an Investigational New Drug (IND) and is not approved by the FDA for human consumption, therapeutic use, or dietary supplementation. It is available exclusively as a research-use-only (RUO) compound for qualified laboratory investigators under applicable federal and institutional guidelines.

What is the half-life of LGD-4033?

The elimination half-life of LGD-4033 (Ligandrol) is approximately 24 to 36 hours following oral administration in clinical research models. This sustained pharmacokinetic profile allows once-daily administration to maintain stable blood plasma concentrations throughout a research protocol, as confirmed by the Bhasin et al. Phase I dose-escalation study.

Does LGD-4033 cause testosterone suppression?

Yes. Clinical data from the Bhasin et al. Phase I trial demonstrates dose-dependent suppression of total testosterone, free testosterone, and sex hormone-binding globulin (SHBG) via HPG axis suppression during LGD-4033 administration. Testosterone levels recovered to baseline within approximately five weeks following cessation at the highest 1.0mg research dose.

How does LGD-4033 compare to RAD-140 (Testolone)?

LGD-4033 exhibits a higher androgen receptor binding affinity (Ki ~1nM) compared to RAD-140 (Ki ~7nM), resulting in more pronounced lean mass effects at equivalent doses in research models. RAD-140 has a significantly longer half-life of approximately 60 hours versus LGD-4033’s 24–36 hours, allowing for less-frequent administration in long-duration studies.

Does LGD-4033 require a Post-Cycle Therapy (PCT) protocol?

Preclinical and Phase I clinical research models show that LGD-4033 induces dose-dependent suppression of the hypothalamic-pituitary-gonadal (HPG) axis. Post-Cycle Therapy (PCT) using selective estrogen receptor modulators (SERMs) such as enclomiphene or tamoxifen is employed in in-vivo research protocols to accelerate endogenous testosterone restoration following compound cessation.

Can LGD-4033 cause liver damage?

Clinical case reports describe cholestatic Drug-Induced Liver Injury (DILI) in subjects self-administering LGD-4033 from unverified sources, with elevated AST and ALT liver enzymes observed. The Bhasin et al. Phase I trial using verified pharmaceutical-grade compound at 0.1–1.0mg reported no significant hepatic enzyme elevation, suggesting product impurities as a primary DILI risk factor.

Is LGD-4033 legal for research purposes?

LGD-4033 is legal to acquire and use strictly for laboratory and in vitro/in vivo research applications in jurisdictions where no explicit prohibition exists. It is not approved as a dietary supplement and FDA Warning Letters issued in 2025–2026 targeted vendors marketing SARMs as such. WADA prohibits LGD-4033 in competitive athletes under the S1.2 classification.

Can LGD-4033 be used alongside GLP-1 receptor agonists in research?

February 2026 data published in the Journal of Clinical Endocrinology & Metabolism highlights LGD-4033 as a candidate adjunctive compound to mitigate the 25–40% lean body mass reduction associated with GLP-1 receptor agonist administration (Semaglutide, Tirzepatide). SARM and GLP-1 co-therapy is an active area of 2026 preclinical research focused on muscle preservation during GLP-1-driven weight loss protocols.

What is the WADA detection window for LGD-4033?

LGD-4033 and its long-chain metabolites are detectable by WADA-compliant liquid chromatography-mass spectrometry (LC-MS/MS) assays for up to 21 days post-administration in research subjects. LGD-4033 is classified under WADA’s Prohibited List (S1.2 — Other Anabolic Agents) and is banned in all sports, both in-competition and out-of-competition.

How long does it take for LGD-4033 to produce measurable effects in research models?

Measurable increases in lean body mass and stair-climbing power were documented in the Bhasin et al. Phase I trial within 21 days of continuous once-daily administration. At the highest 1.0mg research dose, subjects demonstrated a mean lean body mass gain of +1.21 kg, with stair-climbing power improvement occurring in a dose-dependent manner across all three dose cohorts.

Why did Viking Therapeutics pause development of VK5211 (LGD-4033)?

According to Viking Therapeutics’ Q1 2026 earnings report (May 11, 2026), VK5211 has been positioned for external partnering rather than continued internal Phase III development. Viking redirected its primary capital and clinical resources toward VK2735, its GLP-1/GIP co-agonist for obesity treatment, which demonstrated greater commercial potential. VK5211’s IND status and completed clinical data remain available for potential licensing partners.

What is the difference between Ligandrol, Anabolicum, and VK5211?

Ligandrol, Anabolicum, and VK5211 are all synonymous names for the identical chemical compound LGD-4033 (4-[(2R)-2-[(1R)-2,2,2-trifluoro-1-hydroxyethyl]pyrrolidin-1-yl]-2-(trifluoromethyl)benzonitrile). “Ligandrol” is the common research name derived from Ligand Pharmaceuticals, “VK5211” is Viking Therapeutics’ clinical designation, and “Anabolicum” is a legacy trade name. All refer to the same molecular entity with PubChem CID 44137686.

Does LGD-4033 cause hair loss?

Yes, LGD-4033 can trigger a temporary hair shedding condition called telogen effluvium in research subjects. April 2026 UK MHRA guidance documented this association, which occurs because HPG axis suppression disrupts androgen-regulated hair follicle cycling. The condition is generally reversible following compound cessation and hormonal recovery. Research protocols should document dermatological observations alongside standard endocrine monitoring panels.

Can LGD-4033 be detected in anti-doping drug tests?

Yes. WADA-accredited laboratories detect LGD-4033 via LC-MS/MS testing targeting both the parent compound and its dihydroxylated metabolites in urine. These long-chain metabolites extend the detection window to approximately 21 days post-administration. LGD-4033 is classified under WADA Prohibited List S1.2 (Other Anabolic Agents) and banned in-competition and out-of-competition in all sports.

What is the difference between LGD-4033 (Ligandrol) and Ostarine (Enobosarm)?

LGD-4033 (Ligandrol) has a higher androgen receptor binding affinity (Ki ~1nM) compared to Ostarine/Enobosarm (Ki ~4nM), producing greater lean body mass gains at lower doses in clinical models. Ostarine demonstrates a more favorable testosterone suppression profile than LGD-4033, making it preferable for research protocols requiring greater HPG axis preservation. Both are WADA-prohibited SARMs available strictly for Research Use Only.