Andarine (S4): The Cutting SARM With the Vision Tradeoff
Last updated: March 2026
Andarine (S4) is a partial androgen receptor agonist developed by GTX Inc. for muscle wasting and osteoporosis. Its selective tissue activity makes it popular in cutting research, but its well-documented yellow vision side effect sets it apart from other SARMs. All data from preclinical animal studies.
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Oral administration
Not full agonist
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How Andarine Works
Andarine binds the androgen receptor with high affinity but activates it only partially. This partial agonism is theorized to reduce androgenic side effects in non-target tissues while still delivering anabolic signaling in muscle and bone — the hallmark SARM hypothesis.
S4 binds the androgen receptor and acts as a partial agonist — activating the receptor but not to the full extent of testosterone. This partial activation is believed to confer anabolic effects in muscle and bone while producing weaker androgenic signaling in the prostate and scalp.
In preclinical rat models, Andarine demonstrated anabolic effects on skeletal muscle and increased bone mineral density. Its selectivity ratio — anabolic activity relative to androgenic activity — appears favorable compared to testosterone in animal studies. Exact human selectivity is unknown.
Andarine's most well-known side effect is yellow-tinted vision and difficulty adjusting between bright and dark environments. This is attributed to its binding to androgen receptors in retinal cells. The effect is dose-dependent and reversible upon discontinuation. It is a unique distinguishing feature of S4.
In rodent models, Andarine showed reduced androgenic activity in the prostate compared to testosterone, a key therapeutic target in the original research program. GTX developed S4 as a potential alternative to anti-androgens for prostate hypertrophy. Human prostate data does not exist.
What Preclinical Studies Show
⚠️ All data below is from animal studies (primarily rodent models). No approved human clinical trials exist for Andarine. These figures are for research reference only.
Side Effects & Risks
Key Takeaways
- Partial AR agonist with anabolic:androgenic selectivity in animals
- Yellow vision side effect is well-documented and dose-dependent
- Oral bioavailability confirmed — no injection needed
- Half-life ~6-8 hours requires split dosing
- Causes HPG axis suppression requiring post-cycle therapy
- 5-on/2-off protocols reported anecdotally to reduce vision effects
- No approved human clinical trials completed
- Long-term ocular safety is completely unknown
- Exact degree of suppression in humans is uncharacterized
- True anabolic potency in humans vs animal models
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This page is for educational purposes only. It is not medical advice. Andarine (S4) is not FDA approved and is not intended for human use. All data referenced is from preclinical animal studies. Do not use any research chemical without consulting a qualified medical professional.