Description
What Is S4 (Andarine)?
S4, often known as andarine, is a non-steroidal selective androgen receptor modulator (SARM) originally developed by GTx, Inc. for the treatment of muscle wasting, osteoporosis, and benign prostatic hyperplasia. Andarine selectively binds to androgen receptors in skeletal muscle and bone tissue with about one-third the binding affinity of testosterone, while showing markedly reduced androgenic activity in fertility tissues.
Among the first-generation SARMs to undergo extensive lab evaluation, S4 showed potent anabolic effects at doses that produced minimal prostate boost in castrated rat models. The compound’s oral uptake, relatively short half-life of about four to six hours, and well-characterized pharmacological profile have made it a standard reference compound in SARM research. Andarine is very noted in body makeup studies for its power to simultaneously promote lean mass accretion and enhance fat oxidation, a dual-action profile that distinguishes it from many single-mechanism anabolic agents.
Key Features and Specifications
| Specification |
Detail |
| Product Name |
S4 (Andarine) |
| Dosage |
25 mg per capsule |
| Quantity |
60 capsules per bottle |
| Form |
Oral capsule |
| CAS Number |
401900-40-1 |
| Cell-level Formula |
C19H18F3N3O6 |
| Cell-level Weight |
441.36 g/mol |
| Purity |
≥99% (HPLC verified) |
| Testing |
Third-party HPLC and MS test |
| Storage |
Room heat, cool dry place, away from light |
| Classification |
Non-steroidal SARM |
Mechanism of Action: How S4 Andarine Works
Andarine functions as a partial agonist at the androgen receptor, binding with high selectivity to AR in muscle and bone while showing competitive antagonism in prostate tissue. This partial agonist profile creates a unique pharmacological signature: S4 starts anabolic transcriptional programs in target tissues while simultaneously blocking dihydrotestosterone-mediated signaling in androgenic tissues, explaining its original study for benign prostatic hyperplasia.
In skeletal muscle, andarine promotes nitrogen retention and protein synthesis through AR-mediated transcriptional upregulation of myogenic genes. In bone, S4 boosts osteoblast differentiation and mineralization pathways. Lab studies show that andarine restores skeletal muscle mass and bone mineral density in castrated animals to levels approaching those of intact controls, confirming potent tissue-selective anabolism.
The compound’s relatively short half-life of four to six hours allows researchers precise control over plasma levels, making S4 very valuable in dose-response studies and pharmacokinetic modeling. Andarine does not undergo aromatization and does not directly influence estrogen levels.
Reported Research Applications and Benefits
Body makeup research represents the most extensively documented use for S4 andarine. Lab studies consistently show simultaneous lean mass gains and fat mass reductions, with the fat loss component attributed to enhanced fatty acid oxidation in skeletal muscle during androgen receptor start. These dual-action effects position andarine as a key compound in recomposition research.
Bone density research has shown that andarine increases periosteal bone formation, cortical bone thickness, and biomechanical bone strength in ovariectomized rat models, setting up it as a reference compound for osteoporosis and fracture healing studies. Muscle preservation studies in catabolic models confirm that S4 effectively attenuates muscle wasting induced by glucocorticoids, immobilization, and androgen deprivation.
Comparative SARM research often uses S4 as a benchmark compound due to its well-characterized binding kinetics, set up dose-response curves, and extensive published data. Researchers studying andarine vs ostarine or other SARM comparisons benefit from the compound’s documented selectivity index and reproducible pharmacological effects.
S4 Andarine Dosage Information for Research
| Protocol |
Dosage |
Duration |
Notes |
| Standard research dose |
25–50 mg/day |
8–12 weeks |
Split dosing recommended |
| Beginner protocol |
25 mg/day |
8 weeks |
Single daily dose acceptable |
| Advanced protocol |
50 mg/day (split) |
8–12 weeks |
25 mg twice daily |
| Timing |
Split AM/PM |
— |
4–6 hour half-life |
Due to its relatively short half-life of four to six hours, research protocols with S4 often employ split dosing, giving 25 mg in the morning and 25 mg in the evening to keep more stable plasma levels throughout the day. Some protocols incorporate five-days-on, two-days-off cycling schedules to manage vision-related findings reported in higher-dose lab studies.
S4 Andarine vs Ostarine: Key Differences
| Parameter |
S4 (Andarine) |
Ostarine (MK-2866) |
| AR binding affinity |
~33% of testosterone |
~50% of testosterone |
| Main use |
Recomposition (lean mass + fat loss) |
Lean mass preservation |
| Half-life |
4–6 hours |
~24 hours |
| Dosing frequency |
Split (2x daily best) |
Once daily |
| Androgenic activity |
Very low (partial antagonist in prostate) |
Low |
| Suppression possible |
Mild to moderate |
Mild |
| Clinical stage |
Lab |
Phase II completed |
Storage and Handling Instructions
Store S4 andarine capsules at controlled room heat between 20°C and 25°C (68°F to 77°F) in the original sealed container. Protect from direct sunlight, too much heat, and moisture. Under recommended conditions, S4 capsules keep full potency for at least 24 months from manufacture. Do not freeze.
Why Choose PrymaLab S4 Andarine Capsules
Every batch of PrymaLab S4 undergoes independent third-party testing by accredited laboratories using HPLC for purity and mass spectrometry for identity confirmation. Each order ships with a batch-specific Certificate of Test documenting ≥99% purity and full contaminant screening. Pharmaceutical-grade encapsulation ensures precise 25 mg dosing, GMP-compliant manufacturing guarantees consistency, and free priority shipping is included on all domestic orders.
Frequently Asked Questions About S4 Andarine
What makes andarine different from other SARMs?
Andarine is a partial agonist at the androgen receptor, meaning it starts anabolic pathways in muscle and bone while acting as a competitive antagonist in prostate tissue. This dual agonist-antagonist profile, combined with its shorter half-life allowing precise dosing control, distinguishes S4 from full agonist SARMs like RAD-140 and LGD-4033.
Why is S4 andarine dosed twice daily in research protocols?
The relatively short plasma half-life of S4 (about four to six hours) means that a single daily dose produces major peak-to-trough fluctuations. Split dosing, often 25 mg in the morning and 25 mg in the evening, keeps more stable plasma levels and reduces the magnitude of intermittent peak exposure.
Does S4 require post-cycle therapy?
S4 produces mild to moderate suppression of endogenous testosterone at standard research doses. Protocols lasting eight weeks or longer often incorporate a post-cycle therapy phase using SERMs such as enclomiphene or clomiphene. Baseline and endpoint hormone panels are recommended to guide PCT decisions in any research design.
How does andarine compare to ostarine for cutting research?
Andarine is often favored in recomposition and cutting-focused research due to its documented dual-action profile of promoting lean mass while enhancing fat oxidation. Ostarine is often preferred for lean mass preservation during caloric deficit conditions. Both compounds show favorable tissue selectivity profiles in lab data.
What is the purity standard for research-grade S4?
Research-grade S4 andarine should test at ≥99% purity by HPLC test. PrymaLab provides batch-specific Certificates of Test with every order, documenting HPLC purity, mass spectrometry identity confirmation, heavy metal screening, residual solvent test, and microbial testing results from independent accredited laboratories.
Quality Assurance and Testing
PrymaLab keeps pharmaceutical research-grade quality standards for all S4 products. Independent third-party laboratories conduct HPLC purity test, MS identity check, heavy metal screening, residual solvent testing, and microbial assessment on every production batch. Batch-specific Certificates of Test accompany each order, providing full analytical transparency for research records and control compliance.
Research Disclaimer
S4 (andarine) is sold strictly for laboratory research and scientific study purposes only. This product is not intended for human consumption, veterinary use, or treatment use. S4 has not been approved by the FDA or any control agency for medical use. Purchasers must be qualified researchers affiliated with accredited institutions or licensed research organizations. By buying this product, you confirm that it will be used exclusively in accordance with all applicable local, state, and federal regulations governing research materials.
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