Masteron

Masteron is the principal trade name for drostanolone propionate, the 17-beta-propionate ester of 2-alpha-methyl-5-alpha-dihydrotestosterone (2-alpha-methyl-DHT), a synthetic androstane steroid first described in 1959 and introduced to clinical medicine in 1961 following United States Food and Drug Administration approval for the palliative treatment of advanced, inoperable, androgen-responsive mammary carcinoma in postmenopausal women. The compound was developed by Syntex Corporation, licensed to Eli Lilly and Company, and marketed in the United States as Drolban and in European and other international markets as Masteril, Masteron, and Permastril. Drostanolone is a direct structural derivative of dihydrotestosterone (DHT) bearing a methyl group at the carbon-2 alpha position, a modification that confers two pharmacologically consequential properties: resistance to metabolic inactivation by 3-alpha-hydroxysteroid dehydrogenase (3-alpha-HSD) in skeletal muscle tissue, resulting in enhanced anabolic potency relative to the parent DHT molecule; and retention of the intrinsic non-aromatizability of the 5-alpha-reduced steroid nucleus, ensuring that the compound cannot be converted to estrogenic metabolites by the aromatase enzyme complex. As an androgen receptor (AR) agonist, drostanolone binds the AR with high affinity and initiates the canonical genomic androgen signaling cascade, including nuclear translocation, receptor dimerization, coactivator recruitment, and transcriptional activation of androgen-responsive genes governing protein synthesis, nitrogen retention, and musculoskeletal anabolism.

The clinical pharmacology of drostanolone propionate is defined by its intramuscular depot formulation. The propionate ester is hydrolyzed in vivo by tissue and plasma esterases to release the active drostanolone moiety, with an elimination half-life of approximately 2 to 3 days following intramuscular injection. The compound is not orally bioavailable owing to the absence of a 17-alpha-alkyl group; this same structural feature eliminates the hepatotoxicity risk associated with oral anabolic-androgenic steroids such as methyltestosterone and oxymetholone. Protein binding is high, predominantly to sex hormone-binding globulin (SHBG) and albumin. Metabolism proceeds through reduction and conjugation pathways; the principal urinary metabolites include 2-alpha-methyl-5-alpha-androstan-3-alpha-ol-17-one and its glucuronide and sulfate conjugates, which serve as the analytical targets for anti-doping detection.

The registered clinical indication was the palliation of advanced breast cancer in women who were more than one year but less than five years postmenopausal, with documented androgen-responsive or estrogen-receptor-positive disease that had progressed following initial endocrine therapies. Early clinical trials reported objective response rates of approximately 20 to 30 percent, including partial tumor regression and symptomatic palliation. The antitumor mechanism was attributed to competitive androgen receptor-mediated antagonism of estrogen-dependent tumor proliferation, with additional evidence suggesting inhibition of prolactin receptor expression and downregulation of estrogen receptor density in mammary tissue. The clinical application of drostanolone propionate and other androgenic agents in breast cancer was largely superseded in the 1970s and 1980s by the introduction of selective estrogen receptor modulators (tamoxifen) and subsequently by aromatase inhibitors (anastrozole, letrozole, exemestane), which offered comparable or superior efficacy with substantially reduced virilization burden. Drostanolone propionate is no longer marketed in any jurisdiction for the breast cancer indication.

The compound persists in contemporary relevance principally through its widespread non-medical use in performance and physique enhancement contexts, where it is valued for its non-aromatizable androgenic profile, its favorable anabolic-to-androgenic ratio, and its relatively mild side-effect burden compared to other injectable anabolic-androgenic steroids. Drostanolone is classified as a prohibited substance by the World Anti-Doping Agency (WADA) under the category of anabolic agents (S1) and is detectable in urine for up to 3 to 4 weeks following administration through gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry analysis of phase II metabolite conjugates. This monograph reviews the chemistry, synthesis, and stereochemistry of drostanolone propionate; the androgen receptor-mediated mechanism of action including antiestrogenic activity in mammary tissue; the pharmacokinetic profile of the propionate and enanthate ester formulations; the preclinical pharmacology; the clinical evidence base in breast cancer and related indications; sourcing and quality verification considerations; reconstitution and handling; stack interactions with other androgenic and ancillary compounds; adverse events and safety signals; and a comparative assessment of five alternative androgenic or antiestrogenic agents against drostanolone propionate on five competency standards.