Andarine S-4: What the Evidence Actually Shows

What Is Andarine S-4?

Andarine S-4 is a non-steroidal, orally bioavailable SARM first synthesized by GTx Inc. in the early 2000s as part of a research program targeting muscle wasting and osteoporosis. It binds the androgen receptor with high affinity but shows tissue-selective partial agonist activity, meaning it activates androgen signaling more strongly in muscle and bone than in the prostate or skin. GTx halted clinical development before Phase III trials were completed, and no regulatory agency has approved it for human use. The compound remains commercially available through research-chemical suppliers, though the FDA has issued repeated warnings that SARMs sold online are not safe for human consumption.

Andarine's chemical structure, an acetamidine-linked arylpropionamide, distinguishes it from steroidal androgens like testosterone. Because it lacks a steroidal backbone, it does not convert to estrogen via aromatase at standard doses, and it does not bind sex-hormone-binding globulin with high affinity. Both properties were considered pharmacokinetically attractive during early development. However, a partial agonist interaction with the androgen receptor in ocular tissues is believed to explain the yellow-tint and low-light vision complaints that became the primary reason users self-report cycling off the compound [1].

Preclinical work published in Endocrinology demonstrated that andarine maintained muscle mass and bone mineral density in ovariectomized rats at 0.5 mg/kg/day while producing substantially less prostate stimulation than testosterone propionate at equivalent anabolic doses [2]. That tissue selectivity profile attracted significant bodybuilding-community interest, but the absence of human randomized controlled trial data means any claim about precise efficacy in people is speculative.

Mechanism of Action: How Andarine Differs from Testosterone

Andarine acts as a partial agonist at the androgen receptor in muscle and a weak partial agonist in reproductive tissues, producing anabolic effects with a reduced androgenic footprint compared with exogenous testosterone. The androgen receptor co-activator complex recruited by andarine differs from that recruited by dihydrotestosterone (DHT), which accounts for the tissue-selectivity seen in animal models [3].

When andarine binds the androgen receptor, it induces a conformational change that promotes nuclear translocation and transcription of anabolic genes, including insulin-like growth factor 1 (IGF-1) and mechano-growth factor (MGF). This stimulates protein synthesis and nitrogen retention in skeletal muscle. At the same time, the partial agonist profile in prostatic tissue produces markedly less stimulation of prostate-specific antigen (PSA) than full agonists like testosterone or DHT at equianabolic doses, as shown in rodent models [2].

The androgen receptor also exists in the retina's photoreceptor cells. Andarine's partial agonist binding in those cells is thought to interfere with phototransduction, particularly under dim light or when transitioning from bright to dark environments [4]. This mechanism is not fully characterized, but the visual effect appears dose-dependent and reversible upon discontinuation based on user-reported data aggregated in harm-reduction literature.

Unlike testosterone, andarine does not undergo 5-alpha reduction to a more potent androgen, which theoretically reduces scalp and skin-related androgenic effects. However, suppression of the hypothalamic-pituitary-gonadal (HPG) axis still occurs, because circulating androgen receptor agonism signals the hypothalamus to reduce gonadotropin-releasing hormone (GnRH) pulsatility. LH and FSH levels fall, endogenous testosterone production declines, and testicular atrophy may develop with prolonged use [5].

Body-Composition Effects: Animal Data vs. Human Reality

Preclinical data are promising. No completed Phase II or Phase III randomized controlled trial in humans has been published in a peer-reviewed journal as of 2025.

In ovariectomized rat models, andarine at 3 mg/kg/day for 12 weeks produced statistically significant increases in lean body mass and reductions in fat mass compared with vehicle control, without the uterotrophic effects seen with testosterone [2]. A separate rodent study using a castrate model showed that andarine preserved soleus muscle fiber cross-sectional area and femoral bone mineral density to a degree comparable to testosterone at one-quarter the androgen-receptor occupancy [6].

Extrapolating those doses to humans is scientifically unreliable. Allometric scaling from rodent mg/kg dosing to human equivalents typically requires a body-surface-area correction factor of approximately 6.2, meaning a 3 mg/kg rat dose corresponds roughly to a 0.48 mg/kg human dose, or about 34 mg/day for a 70 kg adult. User-reported dosing in bodybuilding communities commonly ranges from 25 to 75 mg/day, which likely exceeds the pharmacologically derived estimate when tissue-sensitivity differences are ignored [7].

The FDA's 2017 warning on SARMs stated directly: "FDA has not approved these drugs for use in humans, and the potential harm from their use is alarming." [8] The agency noted case reports of liver damage, stroke, and cardiac arrest in otherwise healthy adults. A 2020 case report in Hepatology described drug-induced liver injury (DILI) in a 24-year-old male attributable to a SARM product containing andarine analogs, with ALT peaking at 38 times the upper limit of normal [9].

For a comparison point: ostarine MK-2866, the most clinically studied SARM, produced only 1.4 kg of lean mass gain over 12 weeks at 3 mg/day in a 120-person Phase II trial (ENCO-301), which illustrates how modest SARM effects in humans tend to be relative to animal predictions [10].

Andarine vs. Other SARMs: Comparative Profile

Andarine occupies a specific niche relative to ostarine, ligandrol, RAD-140, and cardarine, each of which carries a different risk-benefit estimate based on available data.

Ostarine MK-2866 is the most studied SARM in registered clinical trials. Merck and GTx ran multiple Phase II studies in cancer cachexia and stress urinary incontinence. The ENCO-301 data showed modest lean-mass preservation with a relatively benign short-term safety profile at 3 mg/day, though long-term cardiovascular and hepatic data remain absent [10]. Ostarine's androgen receptor binding affinity is lower than andarine's, producing less HPG axis suppression at equivalent anabolic doses in animal models [11].

Ligandrol LGD-4033 showed 1.21 kg lean-mass gain versus placebo over 21 days at 1 mg/day in a 76-man Boston University Phase I dose-escalation study, with dose-dependent testosterone suppression observed even at that low dose [12]. Ligandrol binds the androgen receptor with higher affinity than andarine and produces more pronounced HPG suppression, making post-cycle recovery more prolonged in user reports.

RAD-140 (testolone) shows the highest anabolic-to-androgenic ratio in preclinical data, approximately 90:1 in rodent models, compared with andarine's approximately 10:1 [13]. A 2020 case report in BMJ Case Reports linked RAD-140 use to severe liver injury and subsequent intracranial hemorrhage in a 52-year-old male with no prior medical history, illustrating the serious adverse-event potential of this compound class [14].

Cardarine GW-501516 is technically not a SARM. It is a PPARδ agonist that GlaxoSmithKline and Ligand Pharmaceuticals abandoned after rodent studies showed a dose-dependent increase in tumor formation across multiple tissue types at 3 mg/kg/day and 10 mg/kg/day over 104 weeks [15]. The FDA has never assigned cardarine an IND for body-composition indications. Its inclusion in the SARM discussion category by the fitness community is pharmacologically inaccurate.

The table below summarizes key comparative data points across these compounds:

| Compound | Human RCT Data | Androgen Receptor Binding | Primary Risk Signal | |---|---|---|---| | Andarine S-4 | None completed | High (partial agonist) | Vision disturbance, DILI | | Ostarine MK-2866 | Phase II completed | Moderate | DILI, HPG suppression | | Ligandrol LGD-4033 | Phase I only | High (full agonist) | HPG suppression, DILI | | RAD-140 | Preclinical only | Very high | DILI, hemorrhagic stroke | | Cardarine GW-501516 | Abandoned | N/A (PPARδ agonist) | Multi-tissue oncogenesis |

Side Effects and Safety Concerns

The three most consistently reported adverse effects associated with andarine are visual disturbances, hepatotoxicity, and testosterone suppression. Each carries clinically meaningful implications.

Vision disturbances occur because andarine's partial agonist activity in retinal androgen receptors interferes with scotopic (low-light) phototransduction. Users report a yellow or greenish tint to vision, especially at night or when moving between differently lit environments. This effect appears dose-dependent and has been reported at doses above 25 mg/day in online harm-reduction surveys aggregated by the Drug Enforcement Administration's Diversion Control Division [16]. The effect resolves in most users within 2 to 4 weeks of discontinuation, but permanent visual changes have not been ruled out because no prospective ophthalmologic studies in humans exist.

Hepatotoxicity is a class-level concern for all SARMs. The FDA's MedWatch database includes multiple SARM-associated DILI reports, and a systematic review of 12 SARM-related liver injury cases published in Alimentary Pharmacology and Therapeutics found a median time to jaundice onset of 42 days from initiation, with cholestatic patterns predominating [17]. Andarine-specific DILI cases are harder to isolate because commercial products frequently contain multiple SARMs or undisclosed additives [8].

Testosterone suppression follows directly from androgen receptor agonism. A 2013 study in Journal of Cachexia, Sarcopenia and Muscle measuring LH and FSH responses to SARM administration confirmed that even partial androgen receptor agonists suppress gonadotropin secretion in a dose-dependent manner [5]. Recovery of the HPG axis after SARM discontinuation typically requires 4 to 12 weeks, and some users report prolonged suppression requiring medical intervention with clomiphene citrate or human chorionic gonadotropin (hCG) [18].

Additional reported adverse effects in the literature include acne, hair shedding, mild fluid retention, and elevations in hematocrit. Cardiovascular risk from lipid profile changes, specifically HDL suppression, has been documented with LGD-4033 and is likely a class effect, though andarine-specific lipid data in humans are not published in peer-reviewed sources [12].

Legal Status and Regulatory Position

Andarine S-4 is not a controlled substance under the United States Controlled Substances Act as of 2025, but it is illegal to sell for human consumption in the United States under the Federal Food, Drug, and Cosmetic Act. The FDA has authority to take action against products marketed as dietary supplements that contain unapproved drugs, and it has done so multiple times against SARM-containing supplement products [8].

The World Anti-Doping Agency (WADA) added all SARMs, including andarine, to its Prohibited List under Section S1 (Anabolic Agents) in 2008 [19]. Any competitive athlete subject to WADA rules who tests positive for andarine faces a minimum four-year suspension under the 2021 World Anti-Doping Code. Andarine and its metabolites are detectable in urine via high-resolution mass spectrometry for at least 72 hours after a single dose, and longer with repeated dosing.

In the United Kingdom, SARMs are classified as prescription-only medicines under the Medicines Act 1968, meaning unlicensed supply is a criminal offense. Canada's Food and Drugs Act similarly prohibits their sale. Australia's Therapeutic Goods Administration classifies SARMs as Schedule 4 prescription substances [7].

The DEA has published guidance indicating it is monitoring SARMs for potential scheduling under the Controlled Substances Act, and the SARMs Control Act of 2019 (H.R. 4771) was introduced in the U.S. House to add SARMs to Schedule III. That bill did not pass but signals ongoing regulatory attention [16].

Clinical Alternatives That Are FDA-Approved

For the indications andarine was originally developed to address, namely muscle wasting and osteoporosis, several FDA-approved options exist with established efficacy and safety profiles.

For muscle wasting in the context of cancer cachexia or HIV-associated wasting, testosterone replacement therapy, megestrol acetate, and oxandrolone (an FDA-approved oral anabolic steroid) are established options. Oxandrolone at 20 mg/day for 12 weeks produced a 2.3 kg lean-mass gain in a randomized trial of 63 HIV-positive men, superior to the lean-mass gains reported with investigational SARMs in human studies [20].

For osteoporosis, FDA-approved therapies include bisphosphonates (alendronate, zoledronic acid), denosumab, teriparatide, romosozumab, and selective estrogen receptor modulators (SERMs) like raloxifene. These agents have 10 to 20 years of fracture-reduction data from large randomized trials and established post-marketing surveillance. The American Society for Bone and Mineral Research guidelines recommend initiating pharmacotherapy when 10-year fracture probability exceeds 20% for major osteoporotic fracture using FRAX scoring [21].

For body-composition optimization in the context of hypogonadism, testosterone replacement therapy under physician supervision remains the evidence-based standard. The Endocrine Society's 2018 clinical practice guideline on testosterone therapy states: "We recommend testosterone therapy for men with symptomatic androgen deficiency to induce and maintain secondary sex characteristics and improve their sexual function, sense of well-being, muscle mass and strength, and bone mineral density." [22]

What Physicians See in Clinical Practice

Patients who present after self-administering andarine or other SARMs typically describe a pattern of initial strength and body-composition gains during the first 4 to 8 weeks, followed by visual symptoms, fatigue consistent with low testosterone, and in some cases, jaundice or right-upper-quadrant discomfort signaling hepatic stress. Laboratory workup typically reveals suppressed LH (often below 1.0 IU/L), suppressed FSH, low-to-low-normal total testosterone, and elevated liver enzymes (AST and ALT).

Management involves discontinuation, supportive care, and monitoring of liver function tests every 2 weeks until normalization. HPG axis recovery is assessed at 6 and 12 weeks post-discontinuation. Persistent suppression beyond 12 weeks warrants evaluation by an endocrinologist and may require pharmacologic HPG axis stimulation. Visual complaints should prompt ophthalmologic referral, including dark-adaptation and electroretinogram testing, because retinal changes have not been formally characterized in a prospective study.

Clinicians should ask about SARM use specifically when evaluating young men with unexplained hypogonadism, elevated liver enzymes, or polycythemia, because patients frequently do not volunteer supplement use without direct questioning. The American Association of Clinical Endocrinology's 2022 update on male hypogonadism notes that drug-induced hypogonadism from non-prescribed anabolic agents is an underdiagnosed etiology in men under 40 [23].

Harm Reduction for Patients Who Decline to Stop

Some patients will continue SARM use regardless of medical advice. A harm-reduction approach, which does not constitute endorsement, includes baseline and interval monitoring of liver function tests, lipid panel, complete blood count, LH, FSH, and total testosterone. Vision changes should prompt immediate dose reduction and ophthalmology evaluation. No dose of andarine has been established as safe in humans.

Patients should be informed that commercial SARM products are frequently adulterated. A 2017 analysis of 44 SARM products purchased online, published in JAMA, found that only 52% contained the labeled compound, 39% contained an unlisted additional compound, and 9% contained no active substance at all [24]. Adulteration increases the unpredictability of any adverse event.

Any male patient using SARMs who wants to preserve fertility should be counseled that HPG suppression reduces spermatogenesis and that recovery is not guaranteed. A semen analysis before initiation and 3 months after discontinuation provides a clinical baseline.