LGD-3303

Overview

LGD-3303 (also written LGD3303 or LGD 3303) is a true nonsteroidal selective androgen receptor modulator (SARM) of the pyrrolo-quinolinone chemical class, synthesized by Ligand Pharmaceuticals. It is NOT a peptide and NOT a steroid — it is a small synthetic molecule that binds the androgen receptor (AR). It appears in this peptide reference only because it is discussed and stacked alongside peptides in the fitness and "research chemical" community, not because it is one.

Its entire evidence base is preclinical — cell assays and rodent studies from around 2008–2009. In animal work it showed a "functionally dissociated" profile: it behaves as a partial agonist for classic androgenic tissue (the ventral prostate) while acting as a full agonist for anabolic tissue (the levator ani muscle and bone). It has never entered human clinical trials, is not approved by the FDA, EMA, or any regulator, and is not a medicine. (Ligand instead advanced a different SARM, LGD-4033 / ligandrol, into human Phase 1 — not LGD-3303.)

Chemistry and structure

LGD-3303 is a small-molecule androgen-receptor ligand, not an amino-acid chain.

Mechanism of action

• High-affinity, nonsteroidal AR binding. LGD-3303 is a nonaromatizable androgen-receptor ligand that binds the human AR with high affinity (Ki ~0.9 nM) and potently activates AR-mediated transcription (EC50 ~3.6 nM), with little or no cross-reactivity at the mineralocorticoid, glucocorticoid, progesterone, or estrogen receptors. [In vitro] (PMID 19017848; Cayman Chemical product data)
• Functional dissociation in vivo. In rodents it acts as a full agonist for anabolic effects (levator ani muscle, bone) but only a partial agonist for classic androgenic effects (ventral prostate, preputial gland). It never stimulated ventral prostate weight above intact/eugonadal levels even at high plasma concentrations, while raising muscle weight above eugonadal levels. [Animal] (PMID 19017848; PMID 18847323)
• Selectivity independent of pharmacokinetics. Tissue selectivity held whether the drug was given orally or by continuous infusion and appeared independent of pharmacokinetics — suggesting the dissociation arises at the receptor/tissue level rather than from differential drug distribution. It was orally bioavailable in rodents. [Animal] (PMID 19017848)
• Bone formation via the periosteum. Its anabolic action on cortical bone occurs in part by stimulating the periosteal surface (bone formation) — a mechanism not shared by bisphosphonates (which act anti-resorptively), giving additive effects in combination. [Animal] (PMID 18847323)

Research and evidence

Human evidence in context. There is none. Every in-vivo result above is from rats, and the mechanistic values are in-vitro/rodent. The "functionally dissociated, prostate-sparing" profile is an animal finding that has never been validated in humans. Human half-life, human pharmacokinetics, human efficacy for muscle or bone, and the human safety profile are all not established / not found in sources.

Status and regulation

• Regulatory approval: None. LGD-3303 is not approved by the FDA, the EMA, or any other regulator for any indication.
• Developer / phase history: Synthesized by Ligand Pharmaceuticals; highest stage reached is preclinical animal pharmacology (~2008–2009). There is no evidence of any regulatory drug-development activity on LGD-3303 continuing after ~2009. Ligand advanced a different SARM, LGD-4033 / ligandrol, into human Phase 1 — not this compound.
• Anti-doping: Prohibited by WADA, listed under Other Anabolic Agents (SARMs), S1.2, on the WADA Prohibited List. WADA is a sport-eligibility axis, separate from legality. (Exact sub-code wording can vary by edition; verify against the current-year WADA List.)
• Market reality: Outside the lab it is sold only as an illicit "research chemical" of unknown identity, purity, and potency.

Safety

Signals, tagged by evidence source:

• No compound-specific human safety data. [Human] All in-vivo data for LGD-3303 are rodent. Cardiovascular, hepatic, endocrine, and long-term risks in humans are entirely uncharacterized for this molecule. (Absence of human trials)
• SARM-class hepatotoxicity / DILI. [Human] The FDA has warned that SARM-containing products are linked to serious health problems including liver injury and acute liver failure; multiple published human case reports describe SARM-associated liver injury requiring hospitalization. These reports are for other SARMs — no LGD-3303-specific human data exist. (FDA consumer/bodybuilding-product warnings; SARM DILI case reports, e.g. PMC8929477, PMC10024817)
• Testosterone / HPTA suppression (class effect). [Hypothesis] HPTA suppression is expected for androgen-receptor agonists, but it has not been measured for LGD-3303 in humans. (SARM class pharmacology)

Product contamination and mislabeling (class-wide). [Human] LGD-3303 is sold only as an illicit research chemical, not a regulated product — a label is not a reliable statement of contents. In Van Wagoner et al., JAMA 2017;318(20):2004-2010 (PMID 29183075), of 44 products sold as SARMs, only 52% actually contained the labeled SARM, 39% contained a different unapproved drug, and ~9% contained no active drug at all. Actual identity, dose, and purity are unverifiable without independent assay.

Legal status

How it compares

LGD-3303 is often grouped with peptides used for muscle and recovery, but the honest comparison is that it is a small-molecule androgen-receptor drug — not a peptide — and, unlike most of its class, it never even reached humans:

• Ligandrol (LGD-4033) — the other, better-known Ligand SARM. The naming is close, but ligandrol reached human Phase 1/2 trials whereas LGD-3303 stopped at rodent pharmacology. Both are nonsteroidal SARMs, unapproved, and WADA-prohibited.
• Testolone (RAD-140) — another nonsteroidal SARM frequently discussed alongside LGD-3303. Like LGD-3303 it is not a peptide and not approved; unlike LGD-3303 it has some human exposure via a clinical program. All share androgen-receptor agonism and WADA-prohibited status.

The decisive point: LGD-3303's "muscle/bone-selective, prostate-sparing" profile is a rat finding only — there is no human data of any kind and no approval anywhere. See the Muscle growth & hormone overview.

Common misconceptions

• "SARMs like LGD-3303 are a mild, safe, or legal alternative to steroids." Not established, and not framed that way here. It has no human safety data at all, belongs to a class the FDA links to liver injury including acute liver failure, is not approved anywhere, and is WADA-prohibited. "Selective" is a mechanistic hypothesis about tissue targeting seen in rats, not a claim of safety.
• "LGD-3303 is a peptide." No. It is a synthetic small molecule (C16H14ClF3N2O, 342.7 g/mol) that binds the androgen receptor. It is covered here only because it is discussed and stacked alongside peptides.
• "It was proven to build muscle and bone." Only in rats. The bone-density and muscle findings, and the additive effect with alendronate, are from ovariectomized rat studies (PMID 18847323). None of it has been validated in humans.
• "LGD-3303 and LGD-4033 are basically the same drug." No. They are distinct compounds from Ligand. LGD-4033 (ligandrol) reached human trials; LGD-3303 never did — its highest stage is preclinical.
• "A product labelled 'LGD-3303' contains LGD-3303." Not reliably. In the JAMA 2017 analysis, 48% of products did not match their label — 39% contained a different unapproved drug and ~9% contained nothing active. You cannot know the contents without an assay.

---

This entry is educational and summarizes published preclinical research and public regulatory information. It is not medical advice, a recommendation, or a guide to obtaining or using any substance.