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.
Quick Reference
Member reference tables summarize the compound's research parameters.
Research Indications
Research Protocols
As reported in cited literature and research-community logs (see Research Citations below), not a personal dosing recommendation.
This member section describes parameters reported in the research literature.
Peptide Interactions
This member section summarizes reported compound interactions and evidence limitations.
Reported Research Time Points
This member section summarizes reported research time points.
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.
This member section discusses research safety considerations and uncertainties.
Quality Indicators
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