LGD-3303

LGD-3303 is a SARM — a selective androgen receptor modulator (a lab-made molecule that switches on the body’s androgen, or male-hormone, receptors in some tissues but not others). It is not a peptide, and it is not a steroid. It came out of the same Ligand Pharmaceuticals research program as LGD-4033 (ligandrol), but it is a separate compound, so it is easy to mix the two up — don’t. Here is the key thing: the only real evidence for LGD-3303 comes from animals. It has never been tested in a human clinical trial, it has never been approved for any use anywhere, and it is banned in sport at all times. Even so, it shows up in research-chemical and bodybuilding circles with muscle-building and even “brain-boosting” claims that the data simply do not back up.

What it is

LGD-3303 is a nonsteroidal SARM — a small molecule that binds to the androgen receptor (AR, the cell docking point that male hormones like testosterone act through). It is not a peptide, and it is not chemically related to anabolic steroids. Its chemistry is well defined: the full chemical name is 9-chloro-2-ethyl-1-methyl-3-(2,2,2-trifluoroethyl)-3H-pyrrolo-[3,2-f]quinolin-7(6H)-one; its CAS number (a unique chemical ID) is 917891-35-1; its formula is C16H14ClF3N2O (molecular weight roughly 342.7). It was discovered by Ligand Pharmaceuticals — that’s where the “LGD” comes from — in the same program that produced LGD-4033/ligandrol. Again, these are different compounds and should not be treated as the same thing.

How does it work? The animal studies describe it as “tissue-selective,” meaning it acts strongly in some places and only weakly in others (researchers also call this “functionally dissociated” activity). In practice, LGD-3303 acts like a near-full switch on the tissues that build muscle and bone, but only a partial switch on the prostate. In castrated rats it raised the weight of the levator ani (a muscle used as a standard marker of muscle-building effect) up to or above normal levels — about as strongly as testosterone — yet it never pushed prostate weight above normal, even when blood levels of the drug were high. In bone, it built up the dense outer layer (cortical bone) and either protected or added to the spongy inner layer (cancellous bone). This kind of “build muscle and bone without overstimulating the prostate” selectivity is the whole theoretical idea behind the SARM class.

The claims

Research-chemical sellers and bodybuilding/biohacking communities pitch LGD-3303 as a powerful way to add lean muscle, gain strength, and “recomp” (lose fat while building muscle). Sometimes they tack on extra angles too — calling it a “nootropic” (a supposed brain or focus enhancer), a beauty aid, or a longevity tool. None of these claims has been confirmed in controlled human studies. The brain-boosting and cosmetic angles in particular are pure marketing, not evidence. The only genuine scientific interest was an idea, not a proven use: rodent data hinted it might one day be relevant to osteoporosis (thinning, fragile bones) and frailty. These products are usually sold with labels like “not for human consumption” or “research use only” — phrases that sound official but carry no real legal weight — even though people buy them to take themselves.

What the evidence actually shows

Human evidence: none. There are no published human clinical trials of LGD-3303. A direct search of ClinicalTrials.gov (the US government registry of clinical studies) turns up zero studies for it. So any claim about how it works or how safe it is in people is just guesswork stretched from animal data. (LGD-4033, the separate compound, did make it into human trials — but those results do not carry over to LGD-3303.)

Animal and preclinical evidence (this part is real):

• Pharmacology and tissue selectivity — Vajda et al. (J Pharmacol Exp Ther, 2009) mapped out how the drug moves through the body and acts on tissues in castrated male Sprague-Dawley rats (a common lab rat strain). This is the study behind the muscle-and-bone-versus-prostate selectivity described above.
• SARM plus bisphosphonate combination — Vajda et al. (J Bone Miner Res, 2009) found that pairing the SARM with alendronate (a bisphosphonate, a standard osteoporosis drug) gave added bone benefits. The main model in this study — and in its title — was the osteopenic, ovariectomized female rat (a female rat with thinning bones and its ovaries removed, a standard stand-in for post-menopausal bone loss). Male rats with the testes removed (orchidectomized) show up only in the early setup work.
• Equine doping-control metabolite profiling — Broberg et al. (J Pharm Biomed Anal, 2023) ran a live horse study and identified roughly eight metabolites (breakdown products the body makes — here, oxygen-added and acid-added forms plus sugar-linked “glucuronide” versions). They proposed one of these, a single-hydroxyl urinary marker, as a target for catching the drug in doping tests.

So the entire usable evidence base is rats and horses. The muscle and “nootropic” benefits claimed for people are unproven.

Legal and regulatory status

LGD-3303 is a research-grade chemical only, still at the early preclinical stage. It has never been approved by the FDA — or any other regulator — for use in humans or animals, and there is no marketing authorization for it anywhere in the world. It has no approved medical use. Chemical and “research” sellers offer it with “not for human consumption” labels, and it circulates in the gray-market SARM and supplement world — but neither that label nor the gray-market setting makes it legitimate. In the US, SARMs are not legal dietary-supplement ingredients and cannot be sold as supplements or drugs. The FDA has warned consumers away from bodybuilding products containing SARMs, pointing to risks that include liver damage, heart attack, and stroke.

In sport, SARMs are banned by WADA (the World Anti-Doping Agency) at all times — both in and out of competition — under Section S1.2, “Other Anabolic Agents.” The ban covers the whole class, and these substances are “non-Specified” (a category that generally carries tougher penalties). LGD-3303 is not on the list of named examples — the 2026 WADA list specifically names andarine, enobosarm (ostarine), LGD-4033 (ligandrol), RAD140, S-23, and YK-11 — but it is still banned as an “other substance with similar chemical structure or biological effect(s).” That means it would still count as a doping violation for a tested athlete. The correct category is S1.2, not S4 (hormone and metabolic modulators). Horse-racing authorities ban it too, which is exactly why the 2023 horse metabolite study was done.

Safety

When it comes to humans, the safety of LGD-3303 is basically unknown. Because there are no human trials, there is no established list of side effects, no safe-dose information, and nothing on long-term use.

The reasonable worries come from what we know about the drug class as a whole, not from human data on LGD-3303 itself:

• Testosterone suppression — Because SARMs switch on the androgen receptor, they are broadly linked to shutting down the body’s own testosterone production (often described as suppressing the HPG axis — the hypothalamus-pituitary-gonad signaling loop that controls sex-hormone levels).
• Liver, cholesterol, and heart concerns — Published case reports from SARM users describe liver injury (including cholestasis, a backup of bile in the liver), worsened cholesterol (lower HDL, the “good” cholesterol), and heart-related concerns. Most of these reports involve other SARMs, such as LGD-4033 — not LGD-3303 specifically.
• Product-quality risk is a real, documented hazard. In an independent lab analysis of 44 products sold online as SARMs (Van Wagoner et al., JAMA, 2017), 48% contained no SARM at all, only about 41% contained the labeled amount, and roughly 25% contained ingredients that weren’t on the label — swapped out or spiked with other SARMs, hormones, or steroids. In plain terms: what’s inside a gray-market vial often does not match what the label says.

The honest bottom line on safety: the evidence is thin, and there is no confirmed human data on whether LGD-3303 works or is safe.

Bottom line

LGD-3303 is a SARM, not a peptide, and a different compound from the better-known LGD-4033. Its real evidence is limited to rat pharmacology, a rat bone-combination study, and a horse doping-control study — there are no human trials at all. It has never been approved for any use, it is not a legal supplement ingredient, and it is banned in sport at all times. The muscle, recomposition, and “nootropic” claims are marketing built on animal data and assumptions about the drug class. The expected class risks — hormone suppression, liver injury, worsened cholesterol, and contaminated products — are real, while any human benefit and safety remain unproven.

Evidence grade: 3/10 · Animal only.

Sources

• Vajda EG, et al. Pharmacokinetics and pharmacodynamics of LGD-3303, an orally available nonsteroidal-selective androgen receptor modulator. J Pharmacol Exp Ther. 2009;328(2):663-670 (PMID 19017848)
• Vajda EG, et al. Combination treatment with a selective androgen receptor modulator (SARM) and a bisphosphonate has additive effects in osteopenic female rats. J Bone Miner Res. 2009;24(2):231-240 (PMID 18847323)
• Broberg MN, et al. Equine in vivo metabolite profiling of the selective androgen receptor modulator LGD-3303 for doping control. J Pharm Biomed Anal. 2023;233:115468 (PMID 37224728)
• Van Wagoner RM, et al. Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet. JAMA. 2017;318(20):2004-2010 (PMC5820696)
• FDA — Certain Bodybuilding Products (SARMs) Put Consumers at Risk of Heart Attack, Stroke, Serious Liver Damage, and More
• USADA — Selective Androgen Receptor Modulators (SARMs), a Prohibited Class of Anabolic Agents (WADA S1.2; prohibited at all times)
• WADA — The Prohibited List (official)