History

LGD-3303 was discovered by Ligand Pharmaceuticals (the source of the "LGD" prefix), the same program that produced LGD-4033/ligandrol — but it is a different, distinct compound. Its tissue selectivity was characterized in castrated male rats by Vajda and colleagues (J Pharmacol Exp Ther, 2009), and it was explored conceptually for osteoporosis and frailty on the basis of rodent data. Development never advanced publicly to human trials, and it later appeared in the gray-market research-chemical and SARM channel.

LGD-3303 is a nonsteroidal selective androgen receptor modulator — a SARM, and importantly a small molecule rather than a peptide. It comes from the same Ligand Pharmaceuticals program as LGD-4033 (ligandrol), but it is a separate compound and should not be confused with it. The only real evidence for LGD-3303 comes from animals: it has never been studied in a human clinical trial, it has never been approved for any use anywhere, and it is banned at all times in sport. Despite that, it shows up in the research-chemical and bodybuilding channel with muscle-building and even “nootropic” framing that the data simply do not support.

What it is

LGD-3303 is a nonsteroidal selective androgen receptor modulator (SARM) — a small-molecule androgen receptor (AR) ligand, not a peptide, and structurally unrelated to anabolic steroids. Its chemistry is defined: 9-chloro-2-ethyl-1-methyl-3-(2,2,2-trifluoroethyl)-3H-pyrrolo-[3,2-f]quinolin-7(6H)-one; CAS 917891-35-1; formula C16H14ClF3N2O (MW ~342.75). It was discovered by Ligand Pharmaceuticals — the source of the “LGD” prefix — the same program that produced LGD-4033/ligandrol. They are different compounds and should not be conflated.

Mechanistically, the preclinical work describes tissue-selective or “functionally dissociated” AR activity: LGD-3303 behaves as a near-full agonist on anabolic tissue (muscle, bone) but only a partial agonist on androgenic tissue (prostate). In castrated rats it raised levator ani muscle weight to or above intact levels with potency similar to testosterone, while only partially stimulating ventral prostate weight even at high exposure. On bone it showed anabolic activity at cortical sites and antiresorptive behavior at cancellous sites. This selectivity is the theoretical basis for the SARM class generally.

The claims

Research-chemical vendors and bodybuilding/biohacking circles market LGD-3303 as a potent compound for lean mass, strength, and recomposition, sometimes with added “nootropic,” cosmetic, or longevity framing. None of these claims has controlled human support — the nootropic and cosmetic angles in particular are marketing, not evidence. The only legitimate scientific interest was conceptual: rodent data suggested possible relevance to osteoporosis and frailty. Products are typically sold labeled “not for human consumption” or “research use only,” which is not a legitimate regulatory status, while being purchased for personal use.

What the evidence actually shows

Human evidence: none. There are no published human clinical trials of LGD-3303 and no clinical-trial registry records for it. Any efficacy or safety claim for humans is unsupported extrapolation from animals. (LGD-4033, a separate compound, did reach human trials — those data do not transfer to LGD-3303.)

Animal and preclinical evidence (real):

Pharmacology and tissue selectivity — Vajda et al. (J Pharmacol Exp Ther, 2009) characterized the PK/PD and tissue-selective AR activity in castrated male Sprague-Dawley rats, the source of the muscle/bone-versus-prostate selectivity described above.
SARM plus bisphosphonate combination — Vajda et al. (J Bone Miner Res, 2009) used both orchidectomized male and ovariectomized female rats; the additive bone effects of combining the SARM with alendronate were the finding in the osteopenic (ovariectomized) female rats, as the published title specifies.
Equine doping-control metabolite profiling — Broberg et al. (J Pharm Biomed Anal, 2023) ran an in vivo horse study (oral 0.05 mg/kg), identifying roughly eight tentative metabolites (hydroxylated/carboxylated species plus glucuronide conjugates) and proposing a monohydroxylated marker detectable in plasma and urine after β-glucuronidase hydrolysis.

So the entire usable evidence base is rodent and equine. The bodybuilding and “nootropic” benefits claimed for humans are unproven.

Legal and regulatory status

LGD-3303 is a research-grade chemical only, at the preclinical stage. It has never been approved by the FDA — or any regulator — for human or veterinary use, and there is no marketing authorization for it anywhere. It has no approved indication. It is sold by chemical and “research” vendors labeled “not for human consumption” and circulates in the gray-market SARM/supplement channel; neither label confers a legitimate regulatory status. In the US, SARMs are not lawful dietary-supplement ingredients, and the FDA has warned against SARM-containing products generally.

In sport, SARMs are prohibited by WADA at all times (in- and out-of-competition) under Section S1.2, “Other Anabolic Agents.” The class ban is categorical. LGD-3303 is not one of the named examples — the official WADA list names exactly six SARMs: andarine, enobosarm (ostarine), LGD-4033 (ligandrol), RAD140, S-23, and YK-11 — but it is still prohibited as an “other substance with similar chemical structure or similar biological effect(s),” making it a doping violation (a non-Specified Substance) for tested athletes. S1.2 is the correct category, not S4 (hormone and metabolic modulators, which covers agents such as AICAR, insulins, and meldonium). Equine racing authorities likewise prohibit it — the basis for the 2023 horse metabolite study.

Safety

Human safety for LGD-3303 is essentially uncharacterized. With no human trials, there is no established adverse-effect profile, no dosing-safety data, and no long-term data.

Reasonable concerns come from the drug class rather than from LGD-3303-specific human data:

HPG-axis / testosterone suppression is broadly associated with SARMs as AR agonists.
Hepatotoxicity (drug-induced liver injury, cholestasis), dyslipidemia (lowered HDL), and cardiovascular concern are described in published SARM-user case reports — mostly involving other SARMs, not LGD-3303 specifically.
Product-quality risk is a documented, real hazard. Gray-market SARM products are frequently mislabeled, under- or over-dosed, or adulterated with other SARMs, steroids, or stimulants; independent analyses have repeatedly found contents that do not match the label.

The honest bottom line on safety: thin evidence overall, with no verified human efficacy or safety data for LGD-3303 specifically.

Bottom line

LGD-3303 is a SARM, not a peptide, and a separate compound from the better-known LGD-4033. Its real evidence is limited to rodent pharmacology, a rodent bone-combination study, and an equine doping-control metabolite study — there are no human trials at all. It has never been approved for any use, it is not a lawful supplement ingredient, and it is banned at all times in sport. The muscle, recomposition, and “nootropic” claims are marketing built on animal data and class assumptions. Expected class risks (hormone suppression, liver injury, adverse lipids, contaminated products) are real, while human benefit and safety remain unproven.

Evidence grade: Animal only.