S4 (Andarine) Research Overview (also known as Andarine, GTx-007, S-4, S40503)
S4, also known as Andarine or GTx-007, is an investigational nonsteroidal selective androgen receptor modulator (SARM) developed by GTx, Inc. It was studied for potential effects on muscle, bone, and androgen-sensitive tissues, but it is not an approved human medicine. S4 is particularly recognized in research and bodybuilding discussions for its reported dose-dependent visual disturbances, including yellow or green color distortion and impaired dark adaptation.
What Is S4?
S4, commonly called Andarine and also identified as GTx-007 or S-4, is an investigational nonsteroidal selective androgen receptor modulator. It was developed by GTx, Inc., the same biotechnology company associated with the development of Ostarine, also known as enobosarm or GTx-024. Andarine was one of the earlier SARM candidates investigated as a possible alternative to conventional androgen therapy. Its development reflected an effort to stimulate androgen receptors in muscle and bone while producing less stimulation of tissues such as the prostate than traditional anabolic-androgenic steroids.
S4 is described as a partial androgen receptor agonist with tissue-selective activity. In research and performance-enhancement discussions, it is associated with simultaneous fat loss and muscle preservation, making it especially popular in descriptions of cutting and body-recomposition phases. Its most distinctive reported adverse effect is not a typical steroid-associated effect but a visual disturbance: yellow or green tinting, altered color perception, and reduced visual adaptation in low-light conditions. These effects are thought to reflect interaction with androgen receptors in ocular tissues, although the precise mechanism and long-term implications remain incompletely characterized. S4 is not approved by the U.S. Food and Drug Administration or comparable regulators for muscle building, fat loss, or any other consumer use, and products sold online may have inaccurate concentrations or contain different compounds.
The term "selective" does not mean that S4 acts only in muscle or that it is free of systemic risks. Selectivity is relative and depends on dose, tissue, receptor biology, metabolism, and the endpoints used in a study. S4 can affect endocrine function, lipids, liver-related laboratory values, mood, fertility, and other androgen-sensitive systems. The available evidence is largely preclinical, supplemented by broader SARM research and anecdotal reports rather than robust, long-term controlled trials of S4 in healthy humans.
Research Indications
Androgen Receptor Selectivity
Nonsteroidal androgen receptor agonism
Andarine (S-4) is a nonsteroidal selective androgen receptor modulator developed to preferentially activate androgen receptors in skeletal muscle and bone relative to some androgen-sensitive tissues.
Tissue-selective signaling hypothesis
Preclinical SARM programs support the concept that ligand-specific receptor conformations can produce different transcriptional effects across tissues; this does not establish clinical safety or selectivity in humans.
Muscle and Lean Mass Models
Anabolic activity in animal studies
Rodent studies of S-4 and related SARMs reported increases in levator ani muscle weight and anabolic effects compared with untreated controls.
Body-composition relevance remains unconfirmed
There are no adequate, approved clinical data demonstrating that S-4 improves lean mass, strength, or athletic performance in healthy people.
Bone Research
Bone-anabolic preclinical rationale
SARM research has investigated androgen receptor activation as a potential means of preserving bone mass in animal models of androgen deficiency.
Not a treatment for osteoporosis
S-4 is not an approved osteoporosis therapy, and fracture-risk reduction, optimal dosing, and long-term skeletal safety have not been established.
Visual-System Effects
Reported night-vision disturbance
User reports and pharmacology discussions commonly describe transient yellow tinting or reduced dark adaptation, possibly related to off-target activity in retinal pathways.
Clinical characterization is limited
The frequency, reversibility, dose relationship, and ophthalmologic significance of visual symptoms have not been adequately defined in controlled human studies.
Research Protocols
As reported in cited literature and research-community logs (see Research Citations below) — not a personal dosing recommendation.
| Research Application | Dose | Frequency | Route |
|---|
| Preclinical reference | Animal-model dependent | Study protocol dependent | Oral |
| Conservative community protocol | 25 mg/day | Split into 2 doses | Oral |
| Common anecdotal range | 25–50 mg/day | Split into 2 doses | Oral |
| Higher-risk anecdotal range | 50 mg/day or more | Split into 2 doses | Oral |
Timing
Andarine is commonly described in researcher communities as having a relatively short apparent duration, leading to split oral administration. No human clinical dosing schedule is approved; visual symptoms, endocrine suppression, lipid changes, and liver markers warrant particular caution.
Peptide Interactions
Concurrent androgenic agents may compound endocrine suppression, adverse lipid changes, acne, mood effects, and other androgen-related risks.
Combining SARMs has no established safety advantage and may add androgen-receptor exposure and suppression risk without controlled evidence of benefit.
A second investigational SARM may increase the likelihood of lipid, hepatic, and hypothalamic-pituitary-gonadal axis effects.
Because orally marketed SARM products may affect liver enzymes or be adulterated, combining them with other liver stressors is inappropriate without clinician oversight.
Potential adverse effects on HDL and LDL cholesterol may complicate cardiovascular-risk management and require clinician-directed monitoring.
Reported yellow visual tinting and impaired dark adaptation can create a practical safety concern for driving at night or operating equipment in dim light.
Reported Research Timeline
01Days 1–3 (reported in cited studies): no reliable beneficial effect should be expected. Some individuals anecdotally report early changes in appetite, energy, or visual color perception.
02Week 1 (reported in cited studies): yellow tinting, difficulty adapting to darkness, headache, or sleep disruption may occur; these effects should not be ignored.
03Weeks 2–3 (reported in cited studies): anecdotal reports may include altered training recovery or muscle fullness, but these observations are not substitutes for controlled efficacy data.
04Weeks 3–6 (reported in cited studies): hormonal suppression, unfavorable lipid changes, and liver-enzyme abnormalities may become more apparent on laboratory testing.
05After discontinuation (reported in cited studies): reported visual effects may improve, but the time course is variable. Follow-up of symptoms and laboratory markers is prudent.
06Weeks to months after cessation (reported in cited studies): endocrine recovery is variable and may be incomplete or delayed; persistent low libido, fatigue, or mood changes require medical assessment.
Safety Notes
Included for harm-reduction awareness only, in the event this compound is encountered outside its labeled research use. Inclusion here does not imply RUO Codes endorses, recommends, or instructs human use.
Andarine is not approved for human use and is prohibited in sport under the World Anti-Doping Agency prohibited list.
Avoid use during pregnancy, while breastfeeding, or when attempting conception; fetal and reproductive risks are unknown.
Avoid use with known liver disease, uncontrolled dyslipidemia, cardiovascular disease, or a history of hormone-sensitive cancer unless specifically directed by a specialist.
Visual changes, particularly yellow tinting or poor dark adaptation, may impair driving and work in low-light environments.
Orally sold products labeled as S-4 may be misbranded, contaminated, or contain undisclosed active drugs; label claims cannot establish identity or dose.
Baseline and follow-up clinical review of blood pressure, lipids, liver enzymes, and reproductive hormones should be clinician-directed.
Seek Medical Attention If:
You develop persistent or worsening vision changes, eye pain, marked light sensitivity, or difficulty seeing at night.
You experience chest pain, shortness of breath, fainting, severe headache, or symptoms of a possible cardiovascular event.
You develop jaundice, dark urine, severe abdominal pain, persistent nausea, or unusual fatigue suggestive of liver injury.
You have severe depression, agitation, suicidal thoughts, or persistent symptoms of hormonal dysfunction after stopping.
Quality Indicators
Verified Marker
Lot-specific third-party COA
Require a recent certificate of analysis linked to the exact lot number, with laboratory identity, test date, sample identification, and reportable results.
Verified Marker
HPLC or LC-MS identity and purity testing
A credible report should identify S-4 by a suitable analytical method and report chromatographic purity, rather than relying on a generic assay statement.
Verified Marker
Oral-unit mg accuracy
For capsules or tablets, look for assay and content-uniformity testing that supports the stated milligrams per unit and minimizes dose variation.
Acceptable Range
Declared excipients and batch traceability
Packaging should provide a batch number, expiry date, storage instructions, manufacturer contact information, and a complete inactive-ingredient declaration.
Quality Concern
Generic, unverifiable, or recycled COAs
Avoid reports without a matching lot number, analytical method, laboratory details, or raw chromatogram; these documents cannot substantiate product identity, purity, or dose.
Research Citations
- The future of androgen therapy: selective androgen receptor modulators.
Gao, W., Kim, J., et al., 2005, Journal of Endocrinology - Pharmacokinetics and pharmacodynamics of nonsteroidal androgen receptor ligands.
Gao, W., Kearbey, J. D., et al., 2006, Pharmaceutical Research - Selective androgen receptor modulators with steroidal structures.
Chen, J., Hwang, D. J., et al., 2005, Endocrinology - Selective androgen receptor modulators: current status and future prospects.
Mohler, M. L., Bohl, C. E., et al., 2009, Steroids - The impact of selective androgen receptor modulators on health and performance.
Dalton, J. T., et al., 2013, Drugs
Research Focus
muscle wasting, fat loss, androgen receptor, bone density, vision effects
Frequently Asked Questions
What should researchers watch for with S4 (Andarine)?
Included for harm-reduction awareness only, in the event this compound is encountered outside its labeled research use. Inclusion here does not imply RUO Codes endorses, recommends, or instructs human use.
What should researchers expect over time with S4 (Andarine)?
Days 1–3 (reported in cited studies): no reliable beneficial effect should be expected. Some individuals anecdotally report early changes in appetite, energy, or visual color perception.
How is S4 (Andarine) typically administered in research?
As reported in cited literature and research-community logs (see Research Citations below) — not a personal dosing recommendation.
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