If you’ve been researching SARMs for cutting, recomposition, or lean muscle retention, chances are you’ve stumbled across S4, also known as Andarine. Touted as one of the “dryest” SARMs on the market, S4 is popular among physique athletes for its ability to increase fat loss, vascularity, and muscle density—without the water retention and bloating of traditional anabolic steroids.
But beneath the surface lies a compound that’s misunderstood, under-researched, and often misused. While it may seem like an ideal shortcut to getting shredded, Andarine comes with its own risks—especially when it comes to vision side effects, suppression, and questionable sourcing.
In this guide, we’ll cover:
→ What S4 is and how it works in the body
→ The benefits you can realistically expect from a properly dosed cycle
→ Potential side effects—especially the notorious “yellow vision”
→ Dosage, cycle length, stacking protocols, and post-cycle therapy
→ Legal status, sourcing concerns, and smarter alternatives
Whether you're just learning about SARMs or you're already considering an S4 cycle, this is the no-nonsense breakdown you need before making any decisions.
What Is S4 (Andarine)?
S4, also known as Andarine, is a Selective Androgen Receptor Modulator (SARM) developed by GTx, Inc. for treating muscle wasting, osteoporosis, and benign prostatic hyperplasia (BPH). Like other SARMs, S4 is designed to bind selectively to androgen receptors in muscle and bone tissue, stimulating anabolic activity without triggering the full-body androgenic effects associated with anabolic steroids.
→ S4 binds with high affinity to androgen receptors in skeletal muscle, promoting lean muscle preservation during caloric restriction
→ It was originally researched as a therapeutic agent to shrink the prostate without affecting muscle mass—an effect not possible with traditional DHT blockers
→ Compared to stronger SARMs like RAD-140, S4 is considered more mild, though still suppressive
→ Its unique chemical structure gives it a short half-life (~4 hours), requiring split dosing throughout the day for steady plasma levels
“Andarine was developed as a non-steroidal SARM capable of retaining anabolic activity in muscle while selectively reducing prostate size, showing promise for both athletic and clinical applications” (Dalton et al., Current Opinion in Clinical Nutrition & Metabolic Care).
Because it doesn’t aromatize into estrogen, S4 does not cause water retention or gynecomastia, making it a preferred option for cutting or recomposition cycles. However, its impact on vision receptors sets it apart from other SARMs—something we’ll explore in detail later.
For a complete breakdown of how SARMs work, check out our guide on What Are SARMs?
How S4 (Andarine) Works
S4 works by selectively binding to androgen receptors in muscle and bone tissue. Once bound, it activates anabolic pathways that promote muscle protein synthesis, nitrogen retention, and bone strength—without stimulating androgen receptors in the prostate, skin, or other tissues prone to unwanted side effects.
→ S4 is a partial agonist of the androgen receptor, meaning it stimulates muscle-building activity without fully activating androgenic effects in non-target tissues
→ It mimics the effects of testosterone in muscle and bone, but avoids many of the unwanted outcomes like prostate enlargement, oily skin, or aggression
→ Compared to other SARMs, S4 has a short half-life (3–6 hours), which requires split dosing (typically twice daily) to maintain stable blood concentrations
→ S4 has a strong anabolic-to-androgenic ratio, contributing to its lean, dry appearance with minimal bloat or water retention
“Andarine exerts its effects through high-affinity binding to androgen receptors in skeletal muscle, promoting anabolic activity with minimal androgenic stimulation in reproductive tissues” (Yin et al., Journal of Medicinal Chemistry).
Its partial agonist profile is a double-edged sword. While it may result in fewer androgenic side effects, it can also mean weaker anabolic effects than full agonists like RAD-140 or LGD-4033. That’s why many users prefer to use S4 in a cutting or recomposition cycle, where preservation and definition matter more than raw mass.
Benefits of S4 (Andarine)
S4 (Andarine) is best known for its ability to enhance muscle hardness, vascularity, and fat loss—all without water retention. This makes it a go-to choice for physique athletes in cutting or recomp phases. While not as powerful for mass-building as LGD-4033 or RAD-140, its lean, dry aesthetic makes it ideal for body composition refinement.
→ Fat Loss and Muscle Retention During a Cut
S4 has been shown to preserve lean muscle mass in a calorie deficit while simultaneously enhancing lipolysis. It doesn’t directly burn fat—but it supports body recomposition by preserving muscle while fat is lost, leading to improved overall definition.
“Selective androgen receptor modulators like Andarine have demonstrated the ability to maintain lean mass during catabolic conditions without increasing androgenic side effects” (Kearbey et al., Endocrinology).
→ Increased Muscle Density and Vascularity
Unlike bulking compounds that add mass and water weight, S4 creates a dense, dry, and defined look. Users often report improved muscle separation, hardness, and increased vascularity within 2–3 weeks of use.
→ No Estrogen Conversion
Because S4 does not aromatize into estrogen, it avoids issues like water retention, gynecomastia, or puffiness—problems commonly associated with steroids like Dianabol or Anadrol. This makes it a strong choice for physique athletes chasing a dry, sharp, contest-ready look.
→ Muscle Preservation for Cutting and Recomp
S4 shines when calories are low. It allows users to hold onto hard-earned muscle while leaning out, making it especially valuable for individuals running long cuts, pre-contest protocols, or summer shreds.
For those seeking a dry, sharp physique without estrogen-related side effects, S4 offers a compelling—though not side effect–free—option.
Side Effects of S4 (Andarine) — Especially the Vision Problem
S4 has a distinct side-effect profile compared to other SARMs, most notably its dose-dependent vision disturbances. Like all SARMs, it can also suppress natural testosterone, disrupt blood lipids, and impact liver enzymes. Treat it like a hormone-modulating drug—not a harmless shortcut.
→ Vision Changes (Night Blindness, Yellow Tint, Light/Dark Adaptation Issues)
Users frequently report xanthopsia (yellow-tinted vision), reduced night vision, and difficulty adjusting between light and dark environments. These effects are believed to stem from S4’s interaction with ocular receptors and typically resolve after discontinuation or dose reduction. They are highly dose-dependent and more common at 50 mg+/day and longer cycles.
“Andarine’s partial agonism and off-target binding have been linked anecdotally to transient visual disturbances, including altered color perception and impaired night vision, which appear reversible upon cessation.” (Basaria, Journal of Clinical Endocrinology & Metabolism).
→ Testosterone Suppression
Despite being marketed as “milder,” S4 suppresses the HPG axis, leading to lowered endogenous testosterone, reduced libido, lethargy, and potential mood changes. You should plan for PCT with a SERM like Clomid or Nolvadex after most S4 cycles—especially if stacked or run beyond 6 weeks.
“Nonsteroidal SARMs can significantly suppress endogenous testosterone and require post-cycle strategies to re-establish HPG axis function.” (Alves et al., Asian Journal of Andrology).
→ Lipid Dysregulation
Like many oral anabolics and SARMs, S4 can lower HDL and raise LDL, increasing long-term cardiovascular risk if abused or run repeatedly without monitoring.
“SARM usage has been associated with adverse lipid remodeling, including decreased HDL and elevated LDL, similar to oral AAS.” (Rahnema et al., Mayo Clinic Proceedings).
→ Liver Enzyme Elevations
Although S4 isn’t a 17α-alkylated steroid, hepatotoxicity and elevated liver enzymes have been reported across the SARM category—often compounded by product contamination or mislabeling in gray-market sources.
“Unapproved SARM products have been implicated in liver injury and other serious adverse events.” (Garey et al., LiverTox / NIH).
→ Mood, Libido, and Energy Swings
Suppression, altered neurotransmitter signaling, and lipid changes can drive mood instability, libido fluctuations, and energy crashes—often becoming most noticeable post-cycle if PCT is skipped or poorly executed. See our SERM overview: Selective Estrogen Receptor Modulators (SERMs).
→ Visual Side Effects During Driving or Night Training
Due to impaired dark adaptation, users should be aware of potential safety risks while driving at night or training in low-light environments. If visual sides become problematic, reduce the dose or discontinue.
S4 (Andarine) Dosage, Cycle Length, and How to Use It Safely
Running an S4 cycle requires more than just picking a dose and hoping for results. Because of its short half-life, suppression risk, and unique side effect profile, timing, dosing strategy, and post-cycle planning are critical. This isn’t a compound to “dabble” with—get it wrong, and you could end up with hormonal crash, visual impairment, or both.
→ Standard S4 Dosage Range
Typical S4 doses range from 25–50 mg per day, split into two doses due to the 3–6 hour half-life.
→ Beginners: 25 mg/day split into 12.5 mg AM / 12.5 mg PM
→ Experienced users: Up to 50 mg/day (split AM/PM), but with higher risk of visual sides
→ Female users: Rarely recommended due to lack of data and risk of virilization
“Andarine has a short half-life, requiring multiple daily doses to maintain consistent plasma concentrations and reduce peak-related side effects.” (Yin et al., Journal of Medicinal Chemistry)
→ Recommended Cycle Length
→ Typical cycle length: 6–8 weeks
→ Advanced users (with PCT plan): up to 10 weeks
→ Post-cycle therapy required: Yes — even at lower doses
S4 is suppressive. If your cycle exceeds 4 weeks at any dosage, plan to use Clomid or Nolvadex for 4 weeks post-cycle.
→ Cycle Example: 8 Weeks
Weeks 1–4:
→ 25 mg/day split into 12.5 mg AM and PM
Weeks 5–8:
→ Increase to 50 mg/day split into 25 mg AM and PM (only if visual sides are manageable)
Weeks 9–12 (PCT):
→ Clomid: 50/50/25/25 mg/day
→ OR Nolvadex: 40/40/20/20 mg/day
→ Best Practices for Safety
→ Start low and increase only if vision sides are tolerable
→ Use a split-dosing protocol to smooth blood concentrations
→ Avoid driving at night if experiencing visual issues
→ Get pre- and post-cycle bloodwork (testosterone, LH/FSH, lipids, liver enzymes)
→ Never use S4 without a PCT plan
→ Only source from labs that provide third-party testing
S4 Stacking Protocols: What Works and What Doesn’t
S4 is most effective in cutting and recomposition stacks where lean muscle retention and fat loss are priorities. Because it doesn’t cause water retention or aromatize to estrogen, it stacks well with other dry compounds—but also increases the risk of testosterone suppression, especially when paired with other SARMs.
Here’s how S4 is commonly used in stacks, and what to avoid:
→ Best SARMs to Stack with S4
→ Ostarine (MK-2866): A mild SARM for preserving muscle during a cut. Stacking Ostarine + S4 provides a synergistic effect on muscle retention and strength without severe suppression (for most users).
→ Cardarine (GW501516): A PPAR-delta agonist, not a SARM, but excellent for increasing endurance, fat oxidation, and stamina during cardio-intensive cuts.
→ MK-677 (Ibutamoren): Boosts growth hormone and helps improve recovery, sleep, and fullness during calorie deficits. Since MK-677 doesn’t suppress testosterone, it pairs well with suppressive SARMs like S4.
“Combining SARMs with non-suppressive agents like MK-677 or Cardarine can help mitigate fatigue and recovery issues without adding to HPTA suppression.” (Rahnema et al., Mayo Clinic Proceedings)
→ Avoid Stacking with Highly Suppressive SARMs
→ Stacking S4 with RAD-140 or S23 can lead to severe testosterone shutdown. These stacks are popular online—but not recommended unless you’re running testosterone base support and planning for a very robust PCT.
“Stacking multiple suppressive SARMs without exogenous testosterone or medical oversight can lead to significant endocrine disruption, often requiring medical intervention.” (Basaria, JCEM)
→ Peptides and Recovery Stack Options
→ Consider adding recovery-focused peptides like:
→ BPC-157 for joint and tendon health
→ TB-500 for soft tissue recovery and inflammation control
→ CJC-1295 + Ipamorelin for GH release and fat loss support during cut cycles
These additions won’t impact testosterone levels but can drastically improve recovery and tissue integrity, especially when training volume is high.
Is S4 (Andarine) Legal?
The legal status of S4 is murky—and depends entirely on where you live and how you intend to use it. In the United States, S4 is not approved for human consumption and is considered a research chemical. It is not a controlled substance, but it is banned for athletic use and often misrepresented in online markets.
→ FDA Status: S4 is not FDA-approved for any medical use and is illegal to sell or market as a dietary supplement or performance-enhancing drug
→ World Anti-Doping Agency (WADA): S4 appears on WADA’s Prohibited List, banned in and out of competition for all athletes
→ USADA Sanctions: Athletes who test positive for S4 face suspensions, fines, and disqualification from competition
→ Sold as “Not for Human Use”: To bypass regulation, S4 is typically labeled as a “research chemical” or “lab use only,” even though it's widely used in bodybuilding communities
“S4, like all SARMs, is prohibited under the WADA Code and has been linked to multiple anti-doping violations across a range of sports.” (WADA, Prohibited List)
Because SARMs are not scheduled substances under federal law, possessing them isn’t necessarily a crime—but buying, selling, or using them outside of research contexts is a legal gray zone. Worse, many products are underdosed, contaminated, or spiked with steroids, making third-party testing essential.
If you're considering alternatives, explore legal compounds like DHEA, MK-677, or recovery peptides like BPC-157 and TB-500.
Common Beginner Mistakes with S4 (Andarine)
S4 is often marketed as a “mild” SARM, which leads many first-time users to underestimate how serious the side effects and suppression can be. Below are the most common mistakes beginners make—and how to avoid them.
→ Mistake #1: Starting at Too High a Dose
Many beginners jump straight to 50 mg/day or more, chasing fast results. This significantly increases the risk of vision side effects, testosterone suppression, and liver stress. Always start low (e.g., 25 mg/day split into two doses) and assess tolerance before increasing.
→ Mistake #2: Ignoring Vision Symptoms
S4’s visual sides (yellow tint, night blindness) are unique to this SARM and are often brushed off. But continuing to increase the dose while vision issues worsen can be dangerous. If sides appear, reduce your dose or take a break—don’t try to “push through it.”
→ Mistake #3: Running Without PCT
Even short cycles of S4 can suppress testosterone. Skipping PCT leads to libido crashes, mood swings, and muscle loss. A 4-week SERM protocol using Clomid or Nolvadex is mandatory for proper recovery.
→ Mistake #4: Using Low-Quality or Mislabeled Products
The S4 market is unregulated, and most products sold online are not lab-tested. Some are underdosed, spiked with steroids, or not S4 at all. Always verify third-party testing or avoid altogether.
“In a 2022 study of 44 SARM products sold online, only 52% contained any active SARM, and 39% contained other unapproved drugs or steroids.” (Evans-Brown et al., BMJ)
→ Mistake #5: No Bloodwork, No Plan
Using S4 without knowing your baseline testosterone, lipids, or liver enzymes is reckless. Track your markers before, during, and after your cycle to manage risk and recovery properly.
Conclusion
S4 (Andarine) is often promoted as a mild, side-effect-free SARM ideal for beginners—but that reputation can be dangerously misleading. While it may deliver noticeable fat loss, muscle hardness, and vascularity, it also comes with real risks: suppression, liver strain, and the infamous vision side effects that no other SARM shares.
→ It works well for cutting and recomposition, especially when paired with compounds like MK-677 or Cardarine
→ But without a PCT plan, bloodwork, and sourcing from a trusted vendor, the risks often outweigh the rewards
→ If you're serious about long-term performance and health, consider safer alternatives like DHEA, BPC-157, or recovery-focused peptides to enhance your results legally and responsibly
S4 isn't for the curious. It's for the informed. If you're not prepared to treat it like a serious hormone-altering compound, you're not ready to use it.
Train hard. Recover smart. And if you're going to enhance—do it with clarity, structure, and a post-cycle plan.
