Not FDA-approved for human use. WADA-banned for tested athletes. Sold as a research chemical; clinical safety beyond short-term trials is not established. This page is educational reference only, not a recommendation or endorsement of use.
- Half-life
- 6 h
- Route
- Oral
- Vision side effects: yellow/green tint, low-light vision difficulty. Dose-dependent, reversible.
- Avoid if you have pre-existing vision conditions or do significant night driving.
Overview
Andarine (S-4) was one of the earliest SARMs developed by GTx Inc., originally investigated for benign prostatic hyperplasia (BPH), muscle wasting, and osteoporosis. Development was halted in Phase II due to vision-related side effects: a yellow/green tint to vision and difficulty adjusting to low light. These effects are dose-dependent and reversible upon discontinuation, but they ended Andarine's clinical development.
It remains popular in the SARM community because of its reputed "drying" effect on physique. Anecdotal reports emphasize hardness and definition rather than raw muscle gain.
Mechanism
Selective androgen receptor agonist with strong affinity for muscle and bone tissue receptors and minimal prostate impact. The vision side effects are believed to result from binding to androgen receptors in the eye (specifically the lipofuscin in retinal pigment epithelium), which interferes with low-light vision processing — a tissue-selectivity miss rather than the intended effect.
Anabolic-to-androgenic ratio in animal models: approximately 3:1 (lower than Ostarine or LGD).
Pharmacokinetics
- Half-life: ~4-6 hours
- Tmax (oral): 1-2 hours
- Bioavailability (oral): moderate
- Metabolism: hepatic
- Elimination: urinary
The ~4-6 hour half-life is short compared with most SARMs, so plasma levels from a single administration decline substantially within the same day.
Expected effects
- Modest lean mass gain (less than Ostarine)
- Pronounced "hardening" or "drying" effect on physique — anecdotally described as the visual signature of Andarine use
- Improved vascularity
- Strength preservation during caloric deficit
- Often used in cutting cycles rather than bulking
Side effect profile
The vision issue is the defining concern:
- Vision changes: Yellow/green tint to vision, especially in low light. Difficulty adjusting from light to dark environments. Some users describe a "purple haze" or trails. The effect is dose-dependent and fully reversible after discontinuation (usually within 1-2 weeks).
- HPTA suppression: Moderate. Less suppressive than RAD-140 or LGD but still requires monitoring at higher doses.
- Lipid changes: Modest HDL reduction.
- Liver: Minimal hepatotoxicity reported.
Bloodwork monitoring
Markers to monitor include a baseline panel, a mid-cycle check around 4 weeks, and a post-cycle panel at approximately 4 weeks after discontinuation:
- Total + Free Testosterone
- LH, FSH
- Estradiol (sensitive)
- Lipid panel
- ALT, AST, GGT
Pharmacokinetic modeling parameters
ka: 2.0 /day
ke: 3.0 /day
Vd: 70 L
F: 0.50
half_life_hours: 5.5
Notes and caveats
- The vision side effects are the dealbreaker for many users — even at low doses, low-light driving (night driving) becomes uncomfortable.
- Discontinuation reverses the vision effects, but users with pre-existing vision conditions should avoid entirely.
- Short half-life means missed doses meaningfully affect plasma levels — adherence matters more than for once-daily compounds.