S 23 (Mastorin)

S-23 Mastorin Dragon Pharma — Overview

S-23 Mastorin Dragon Pharma is the highest-potency selective androgen receptor modulator (SARM) currently available, supplied at 10 mg per tablet. S-23 binds the androgen receptor with greater affinity than any other SARM, producing anabolic effects on muscle and bone that more closely approach those of traditional anabolic steroids than any compound in its class. Unlike most SARMs, which produce partial or low-level HPTA suppression, S-23 causes significant and consistent suppression of LH and FSH — comparable to a moderate-dose AAS cycle — and requires a proper PCT protocol at the conclusion of every run regardless of dose.

S-23 does not aromatize, produces no water retention, and delivers fully dry lean-mass gains with simultaneous fat-loss properties, making it one of the most effective body-recomposition compounds in the SARM category. Originally studied as a male hormonal contraceptive due to its potent FSH/LH suppression, its performance applications center on lean bulking, contest preparation, and recomposition phases where dry, quality gains are the priority. Available at Steroid Warehouse at 10 mg/tab, S-23 is dosed twice daily to account for its approximately 12-hour half-life and maintain stable plasma levels.

About the Compound: S-23

S-23 is a non-steroidal SARM developed originally by GTx Inc. as a potential male hormonal contraceptive. Its chemical structure — a halogenated arylpropionamide — allows it to bind the androgen receptor (AR) with exceptionally high affinity and full agonist activity in anabolic tissues (muscle, bone) while producing tissue-selective, partial antagonist effects in reproductive tissues (testis, prostate) at lower doses. At performance doses (15–30 mg/day), the dominant pharmacological effect is potent anabolic AR activation throughout skeletal muscle with concurrent robust HPTA suppression.

The degree of HPTA suppression is the key clinical distinction between S-23 and other SARMs. Compounds like Ostarine (MK-2866) or even LGD-4033 produce partial suppression from which natural testosterone recovery occurs relatively quickly and sometimes without formal PCT. S-23 at doses above 10 mg/day suppresses LH and FSH to near-zero consistently, producing a hormonal environment analogous to an anabolic steroid cycle: testosterone production shuts down, and recovery requires active intervention through SERM-based PCT. This suppressive profile is a direct consequence of the compound's high AR binding affinity and full agonist activity at hypothalamic and pituitary AR, which triggers strong negative feedback on GnRH and gonadotropin release.

S-23 has a half-life of approximately 11.9 hours, necessitating twice-daily dosing (morning and evening) to maintain stable plasma levels and avoid concentration troughs that would reduce anabolic signaling consistency. With Dragon Pharma's 10 mg/tab format, the standard 15 mg/day protocol uses one tab in the morning and half a tab (5 mg) in the evening, while the 20 mg/day protocol uses one tab twice daily.

What S-23 Does

• Lean muscle mass accrual with zero water retention — S-23's high-affinity AR binding in skeletal muscle drives anabolic signaling at a level meaningfully above other SARMs; gains are fully dry and appear quickly — within 2–3 weeks at doses of 15 mg/day and above; a well-executed 8-week cycle at 20 mg/day with adequate training and caloric surplus typically yields 4–7 kg of lean mass; because there is no aromatization and no water retention, all mass gained is functional; cuts and muscle definition visibly improve even when calories are maintained at maintenance
• Significant strength increases — androgenic drive on the CNS and neuromuscular junction is a well-documented effect of AR agonism; S-23 produces strength increases that begin in week 2–3 and accelerate through week 6–8; the strength effect is more pronounced than with Ostarine or LGD-4033 and approaches that of mild anabolic steroid use; trained athletes typically report 5–10% progression on compound lifts across an 8-week run
• Simultaneous fat loss (body recomposition) — AR activation in adipose tissue promotes lipolysis; S-23's potency at the AR produces measurable fat-loss effects even in a slight caloric surplus; in a caloric deficit, the fat-loss rate is amplified while lean mass is preserved due to the anabolic AR signaling in muscle; this dual fat-loss and lean-mass preservation effect makes S-23 one of the most effective single-compound recomposition agents in the SARM class
• Bone mineral density improvement — AR agonism in osteoblasts promotes bone formation; S-23 was originally studied for its anabolic effects on bone; at performance doses it produces meaningful increases in bone mineral density over 6–8 weeks; this is clinically relevant for athletes under repetitive mechanical stress or with low baseline bone density
• No estrogen-related side effects — S-23 does not undergo aromatase-mediated conversion to estradiol; circulating E2 does not increase during an S-23 cycle; gynecomastia, water retention, and blood pressure elevation from estrogenic pathways are not concerns; the hormonal environment during S-23 use is defined by elevated androgen signaling at the AR with stable or mildly declining E2 (as endogenous testosterone falls due to HPTA suppression); an aromatase inhibitor is not required or appropriate

Who It's For

• Intermediate-to-advanced athletes who have completed at least one SARM cycle and understand PCT protocols — S-23 is not an entry-level SARM; its HPTA suppression profile requires the same management awareness as a mild AAS cycle; users who have run Ostarine or LGD-4033 and are ready to step up to the highest-potency SARM available while remaining within the SARM category are the primary target; it is also used by AAS-experienced athletes who want a dry-gains phase between heavier compound cycles
• Athletes prioritizing dry gains, body recomposition, or contest preparation — where compounds like Testosterone produce wet gains alongside muscle from aromatization, S-23 produces exclusively dry, dense lean mass; for athletes whose goal is conditioning, muscle definition, and visible recomposition rather than maximum scale weight, S-23 delivers the highest quality gains of any SARM; it is particularly effective in 6–8 week cutting or recomposition phases
• What differentiates S-23 from similar alternatives: compared to LGD-4033, S-23 has higher AR binding affinity and greater anabolic output but is more suppressive and requires more diligent PCT; LGD-4033 is often considered the standard potent SARM — S-23 is a meaningful step above it in both efficacy and suppression; compared to YK-11, S-23 is a pure AR agonist while YK-11 adds myostatin inhibition; both are high-potency options but operate through different mechanisms; YK-11 may offer greater raw mass ceiling while S-23 produces more predictable and dose-linear anabolic response; compared to Ostarine (MK-2866), S-23 is dramatically more suppressive and more anabolically potent — Ostarine is appropriate for first-time SARM users and those prioritizing minimal suppression, while S-23 is for users who need maximum SARM output and are prepared for the corresponding PCT requirement
• Users who should choose something else: first-time SARM users should start with Ostarine or LGD-4033 before running S-23; users unwilling or unable to run a proper 4-week PCT should not use S-23 at any dose; users with an existing active hormonal issue (low testosterone, fertility concerns) should address those before introducing a highly suppressive compound; S-23 at doses above 20 mg/day may produce androgenic side effects (acne, increased aggression) that are inconsistent with the typical SARM-use expectation of minimal androgenic activity

S-23 vs Alternatives

Combinations

Side Effects & Management

Bloodwork Monitoring

PCT

PCT after S-23 is mandatory at every dose and cycle length. Unlike Ostarine or low-dose LGD-4033 where "natural recovery without PCT" is sometimes discussed, S-23's suppression depth makes this option unreliable and high-risk. The PCT goal is to rapidly restore LH and FSH, which then reactivate testicular testosterone production and restore HPG axis function within 4–6 weeks.

PCT start timing: begin the day after the last S-23 tablet. No ester clearance waiting period applies (S-23 is a non-esterified oral SARM with a ~12-hour half-life; it clears completely within 48–72 hours of the last dose).

Practical Summary

References