What is S4 (Andarine)?
S4, known as Andarine, is a SARM developed by GTx Inc. with early research dating back to the early 2000s. It was one of the first SARMs to show strong preclinical results for muscle preservation and bone density in animal models. Despite its early promise, clinical development was paused — largely due to visual disturbances observed in research subjects.
⚠ Research Purposes Only: S4 Andarine is a research chemical not approved for human consumption by the FDA or MHRA. Visual disturbances have been reported in research contexts.
S4 Selectivity & Anabolic Research
Preclinical research on S4 demonstrated partial agonist activity at the androgen receptor in muscle and bone tissue, while acting as an antagonist in the prostate — a key selectivity goal for SARM research.
| Tissue | S4 Action | Research Finding |
|---|---|---|
| Muscle | Partial Agonist | Anabolic activity in animal models |
| Bone | Partial Agonist | Bone density preservation |
| Prostate | Antagonist | No growth stimulation in models |
| Eyes (retina) | Partial binding | Yellow-tint visual disturbances noted |
Visual Side Effects in Research
The most significant finding in S4 research is dose-dependent visual disturbances — specifically a yellow tint to vision, particularly in low-light conditions. This occurs due to S4 binding to a retinal receptor (AR in the eye). Research indicates this effect is reversible upon discontinuation.
This is a critical data point for researchers — the visual side effect profile was a primary reason clinical development of S4 did not progress as far as compounds like Ostarine or RAD-140.
S4 vs Other SARMs — Research Status
| SARM | Human Trials | Visual Effects | Development Status |
|---|---|---|---|
| S4 (Andarine) | Limited | Yes (dose-dependent) | Paused |
| Ostarine (MK-2866) | Phase II | No | Active research |
| RAD-140 | Phase I | No | Active research |
| LGD-4033 | Phase I | No | Active research |
🔬 Where to Source S4 Andarine for Research (USA & UK)
For USA and UK researchers, SwissChems is one of the most reliable sources with third-party certificates of analysis. All products are for research purposes only and not approved for human consumption.
Visit SwissChems →⚠ Affiliate link — use code Tomjunkie for 20% off. Research purposes only.
Frequently Asked Questions
S4 partially binds to androgen receptors in retinal tissue, causing yellow-tint vision disturbances particularly in low light. Research indicates this is reversible on discontinuation. S4 is a research chemical only.
S4 and RAD-140 have different selectivity profiles. RAD-140 has more published human clinical data. S4's clinical development was paused partly due to its visual side effect profile.
SwissChems is a highly-rated vendor for S4 Andarine with HPLC certificates of analysis. For research purposes only.
S4 is a partial agonist at androgen receptors and is expected to cause some HPTA suppression. Research protocols should account for hormonal recovery post-discontinuation.