S 23 (Mastorin)

S23 (Mastorin) — Full AR Agonist SARM by Dragon Pharma

S23 (Mastorin) is Dragon Pharma's formulation of the most potent non-steroidal SARM in the current range at 10mg per tablet — a full androgen receptor agonist in muscle tissue developed by GTx Inc. with exceptionally high AR binding affinity. S23 was originally investigated as a male hormonal contraceptive rather than a performance compound — at sufficient doses it produces complete suppression of spermatogenesis, which was its intended therapeutic application. This research origin reveals the critical practical reality of S23: it is the most suppressive SARM in the Dragon Pharma range, requiring the same PCT attentiveness as an injectable AAS cycle and, at higher doses, potentially deeper suppression than LGD-4033.

Also searched as: S23 Mastorin, S23 SARM, S-23 10mg, Mastorin Dragon Pharma, S23 cutting SARM.

S23 as a Male Contraceptive — The Research Context That Explains Its Suppression

Understanding S23's suppression requires understanding its original research purpose:

• GTx Inc. investigated S23 specifically as a male hormonal contraceptive — the aim was to suppress spermatogenesis completely through HPG axis androgen feedback, similar in concept to female hormonal contraception. The SARM approach was chosen because it could theoretically suppress spermatogenesis (via HPG/FSH suppression) while minimising systemic androgenic side effects compared to testosterone-based male contraceptives
• In rodent studies, S23 produced complete reversible suppression of spermatogenesis at contraceptive doses — confirming full HPG axis suppression. Spermatogenesis recovered post-cessation, confirming reversibility
• This contraceptive research context directly informs performance use: S23 at typical performance doses (10-20mg/day) produces substantial, potentially complete, FSH and LH suppression. Testosterone levels fall to hypogonadal levels during use; PCT is mandatory and should be approached as seriously as after a testosterone injectable cycle
• S23 has no completed human clinical trials — all published data is rodent-based. This is a meaningful limitation on safety characterisation compared to LGD-4033 (Phase I) or Ostarine (Phase III) which have human pharmacokinetic data

S23 vs Other SARMs — Where It Sits in the Hierarchy

S23 vs Masteron — Two Very Different Hardening Mechanisms

S23 is called "Mastorin" — a name evoking Masteron (Drostanolone) — and both produce hardness and enhanced muscle density, but through fundamentally different mechanisms:

• Masteron (Drostanolone) is a DHT-derived injectable steroidal androgen. Its hardening effect comes from: direct AR activation in muscle tissue; internal aromatase inhibition (reduces estrogen conversion); and DHT's direct peripheral anti-estrogenic effect. Masteron requires injection, has a short half-life (Propionate) or longer ester (Enanthate), and carries the full androgenic profile of a DHT compound including scalp/prostate activity
• S23 is a non-steroidal oral AR agonist. Its hardening effect comes from: high-affinity full AR agonism in muscle tissue producing lean mass retention and reduced water retention (unlike aromatising compounds); and significant reduction of body fat through androgenic stimulation of lipolysis. S23 does not carry the DHT-related scalp/prostate activity of Masteron (tissue selectivity), does not aromatise, and is oral
• Both produce similar visual results (hardness, dryness, vascularity) through different molecular pathways — Masteron is a proven pharmaceutical compound with decades of use data; S23 has only rodent safety data

Effects and Benefits

• Lean mass preservation and enhancement — high-affinity full AR agonism in muscle maintains and builds lean tissue even during caloric deficit
• Muscle hardness and density — non-aromatising, producing dry gains without estrogenic water retention
• Body fat reduction — androgenic stimulation of lipolysis; documented fat mass decrease in animal studies alongside lean mass preservation
• Bone density support — S23 showed bone anabolic effects in rodent studies — relevant for injury prevention during aggressive cutting
• Vascularity — reduced subcutaneous water from non-estrogenic profile

Dosage and Administration

The ~12-hour half-life requires twice-daily dosing (morning and evening) for stable blood levels. Never exceed 8 weeks — suppression depth at 20mg/day for extended periods produces recovery challenges. PCT begins 24-48 hours after the last tablet. Given suppression depth, HCG pre-PCT (or during cycle) is more strongly advisable with S23 than with other SARMs. Never stack S23 with other highly suppressive compounds without understanding the additive suppression burden.