Andarine (S-4)

Overview

Andarine (development code S-4 or GTx-007, also called androxolutamide) is an investigational nonsteroidal selective androgen receptor modulator (SARM). Chemically it is a small-molecule arylpropionamide bearing a nitro group — it is NOT a peptide and NOT an approved medicine. It appears on this peptide reference because it is frequently discussed and stacked alongside peptides in the fitness and "research chemical" community, not because it is one.

Andarine was developed by GTx, Inc. and is widely regarded as likely the first SARM to enter human clinical testing. Its human evidence is limited to a small, early, pre-registry Phase 1 program (about three studies, roughly 86 healthy volunteers, around 2003–2004). A planned Phase 2 (2004) never proceeded, and the program was ultimately abandoned.

Chemistry and structure

Andarine is a nonsteroidal arylpropionamide small molecule, not an amino-acid chain. Its full chemical name is S-3-(4-acetylamino-phenoxy)-2-hydroxy-2-methyl-N-(4-nitro- 3-trifluoromethyl-phenyl)-propionamide — note the nitro (4-nitro) group in its structure.

Mechanism of action

• Androgen receptor (AR) partial agonist. Andarine binds the androgen receptor and acts as a tissue-selective partial agonist. The SARM design goal is to drive the anabolic program in muscle and bone while producing less stimulation of androgen-sensitive reproductive tissue (e.g., the prostate) than testosterone — attributed to different receptor conformations and cofactor recruitment. [In vitro]
• Anabolic effects on muscle and bone. In castrated (orchidectomized) male rats, andarine restored skeletal-muscle mass and strength and helped preserve bone, with a weaker effect on the prostate than dihydrotestosterone. [Animal]
• Retinal / ocular effect (the abandonment signal). The dose-dependent yellow- tinted vision and impaired night vision seen in humans is commonly attributed to androgen-receptor activity in ocular tissue (retina/lens); the exact mechanism is not established in these sources. The disturbance was reversible when the drug was stopped. [Human] observation; [Hypothesis] mechanism.

Research and evidence

Human evidence in context. Human data are limited to a small, early Phase 1 program from roughly two decades ago. Because these were pre-registry studies (before ClinicalTrials.gov registration was routine), they are cited by PMID, not by an NCT number. There are no completed, published human trials establishing andarine's efficacy for muscle growth, fat loss, athletic performance, or any medical indication. The anabolic muscle/bone claims rest on animal work. Human pharmacokinetics (bioavailability, half-life) were not found in these sources.

Status and regulation

• Regulatory approval: None. Andarine is not approved by the FDA, the EMA, or any other regulator for any indication. Its development was abandoned after Phase 1 because of the visual disturbance described above; a planned Phase 2 in 2004 never proceeded.
• Anti-doping: Prohibited by the World Anti-Doping Agency (WADA) at all times (in- and out-of-competition), classified under Anabolic Agents — Other Anabolic Agents (S1.2), where andarine is explicitly named alongside other SARMs (per USADA's summary of the Prohibited List). WADA sport-eligibility is a separate axis from legality.
• Market reality: It is sold only as a "research chemical" and circulates on the black market despite never having been approved. Such products are of unknown identity, purity, and potency (see Safety, below).

Safety

The overall picture: andarine has a known, drug-specific ocular signal, sits within a drug class the FDA has flagged for liver injury and other serious harms, and — as an unregulated research chemical — carries the additional, separate hazards of contamination and mislabeling.

Legal status

How it compares

Andarine is often grouped with other SARMs and "recomposition" research chemicals, but each has its own distinct profile and none is an approved physique/performance drug:

• Cardarine (GW-501516) — frequently sold and stacked alongside SARMs, but it is not a SARM: it is a PPARδ agonist whose development was abandoned over a rodent cancer signal. Different receptor, different defining hazard.

The honest framing: andarine is an abandoned, unapproved research reagent with a documented visual side effect and class-wide FDA-flagged risks — it is not a "milder, safer, or legal alternative to steroids." See the muscle growth & hormone overview.

Common misconceptions

• "Andarine is a peptide." No. It is a nonsteroidal arylpropionamide small molecule (C19H18F3N3O6, 441.4 g/mol) with a nitro group. It is covered here only because it is discussed and stacked with peptides.
• "SARMs like andarine are a safe, legal alternative to steroids." No. Andarine is not approved, was abandoned over a visual side effect, and its drug class is FDA-flagged for liver injury and testosterone suppression. It is prohibited in sport and sold only as an unregulated research chemical.
• "The vision problem is minor / permanent damage." The disturbance was dose-dependent and reported as reversible on stopping — but it was serious enough to end the drug's development. That it reverses does not make it trivial.
• "If it's labeled andarine, that's what's in it." Not reliably. In the JAMA 2017 analysis, only about half of products sold as SARMs contained the labeled compound; many contained a different drug or nothing active.

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This entry is educational and summarizes published research and public regulatory information. It is not medical advice, a recommendation, or a guide to obtaining or using any substance. Not legal advice — check your own jurisdiction. Last reviewed 2026-07-10.