S 23 (Mastorin) by Dragon Pharma

Dragon Pharma Original Formula

S23 (Mastorin)

S23 SARM•10 mg/tab
Class Non-Steroidal Full AR Agonist SARM
Half-Life ~12 hours
Anabolic Potency High — Near Full AR Agonism
Suppression High — Male Contraceptive Research
Pack 100 tabs
Form Oral Tablet
Manufactured by Dragon Pharma Third-Party Tested
Availability: In Stock
$105.00
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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

SARM AR Binding Anabolic Effect Suppression Human Data Best Use
Ostarine (MK-2866) Partial agonist Mild-moderate Mild Phase III First SARM; lean mass; injury
LGD-4033 Full agonist High Significant Phase I Mass; strength; recomposition
S23 Full agonist — highest affinity High High to complete Preclinical only Cutting; hardness; body recomposition
YK-11 Partial — myostatin inhibitor Very high Significant Preclinical only Myostatin inhibition; strength

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

Experience Level Daily Dose Cycle Length PCT
First S23 cycle 10 mg/day 6 weeks Full 4-6 week PCT — mandatory
Experienced 15–20 mg/day 6–8 weeks Full PCT; consider HCG pre-PCT

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.

PCT for S23

  • Clomid — 50mg/day for 2-3 weeks, then 25mg/day for 2-3 weeks; a 6-week PCT is advisable at 15-20mg/day S23 doses
  • Nolvadex — 40mg/day for 2 weeks, then 20mg/day for 2-4 weeks; can be combined with Clomid for deeper suppression recovery
  • HCG 5000IU — given S23's complete spermatogenesis suppression potential, HCG use during cycle or as a pre-PCT Leydig cell reactivation protocol is more strongly indicated than for milder SARMs

Stacking Context

  • GW-501516 (Cardarine) — non-suppressive PPARδ endurance and fat oxidation; adds metabolic fat burning to S23's AR-mediated lean mass and hardness during a cut without additional suppression
  • MK-677 — non-suppressive GH/IGF-1 elevation; counters the potential GH reduction during caloric deficit cutting and supports recovery without adding HPG burden

"S23 was developed as a male contraceptive because it suppresses spermatogenesis completely — this research origin is the most accurate characterisation of its HPG suppression depth. At performance doses, S23 demands the same PCT rigour as an injectable AAS cycle, not the mild recovery protocols sometimes applied to other SARMs."

Storage and Handling

Store S23 at room temperature, away from direct sunlight and moisture. Keep in original packaging until use.

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S23 was investigated by GTx Inc. for male hormonal contraception because of its unusually complete HPG axis suppression at sufficient doses. The concept was analogous to female hormonal contraception — an exogenous androgenic signal suppressing the HPG axis to eliminate FSH-driven spermatogenesis. S23's SARM selectivity was intended to provide HPG suppression and contraceptive effect while minimising the systemic androgenic side effects of testosterone-based male contraceptives. In rodent studies it achieved complete, reversible spermatogenesis suppression — confirming the depth of its HPG effect that is directly relevant to performance users.

Both produce significant HPG suppression requiring full PCT, but S23's suppression depth is generally considered greater at equivalent doses — reflecting its higher AR binding affinity and more complete receptor agonism. LGD-4033 at 10mg/day typically suppresses testosterone by 50-70%; S23 at 15-20mg/day can approach near-complete LH/FSH suppression, similar to injectable AAS cycles. This makes HCG use during or before PCT more strongly advisable with S23 than with LGD-4033, and a 6-week PCT more warranted than the 4-week protocol sometimes adequate for LGD-4033.

S23's profile — high-affinity full AR agonism with no aromatisation, lean mass preservation, androgenic stimulation of fat oxidation, and hardness/density effects — aligns optimally with cutting phase goals. Its androgenic potency maintains muscle while caloric deficit would otherwise drive catabolism; its non-aromatising nature eliminates estrogenic water retention; and animal studies documented fat mass reduction alongside lean mass preservation. For mass building, LGD-4033's somewhat broader anabolic profile is generally preferred.

The "Mastorin" name evokes Masteron but the compounds are pharmacologically unrelated. Masteron is a DHT-derived injectable steroidal androgen with decades of pharmaceutical history, hardening effects via internal aromatase inhibition and peripheral anti-estrogenic activity, and the full androgenic profile of a DHT compound including scalp and prostate sensitivity. S23 is a non-steroidal oral SARM with tissue selectivity — AR agonism in muscle without DHT-pathway scalp/prostate activity, no aromatisation, and no injection. Both produce hardness and dryness but through entirely different mechanisms and with different safety profiles.

No — S23 has only preclinical (rodent) data. This is a significant distinction from LGD-4033 (Phase I in humans) and Ostarine (Phase III in humans) which have documented human pharmacokinetics and safety profiles. S23's performance use therefore involves extrapolating from animal data and community experience rather than established human safety parameters. This absence of human data should be weighed when assessing risk — particularly given S23's complete HPG suppression potential.

24-48 hours after the last tablet — the ~12-hour half-life clears S23 relatively quickly. However, given S23's suppression depth, the practical recovery timeline from the underlying HPG suppression is longer than a short half-life might suggest. A 6-week PCT with Clomid and/or Nolvadex is advisable for cycles of 15-20mg/day for 6-8 weeks. Pre-PCT HCG (1,000-2,000IU daily for 5-10 days before SERM PCT) is more strongly indicated with S23 than with milder SARMs given its documented spermatogenesis suppression potential.

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