Masteron

Androgen Receptor Agonism in Muscle#

Drostanolone is 2α-methyl-dihydrotestosterone — a 5α-reduced DHT scaffold with a methyl group at the 2-position. That 2α-methyl is the whole trick: pure DHT gets chewed up by 3α-hydroxysteroid dehydrogenase in skeletal muscle almost as fast as it arrives, which is why DHT itself is a useless anabolic. The 2α-methyl blocks that inactivation, letting drostanolone survive in muscle tissue long enough to occupy the androgen receptor and drive the standard AR-mediated anabolic program: increased protein synthesis, myonuclear accretion, and strength expression. AR affinity in both muscle and prostate is high, which is also why it hits scalp and prostate tissue in susceptible users.

"Drostanolone demonstrated high relative binding affinity for the androgen receptor in both skeletal muscle and prostate, as well as strong affinity for sex hormone-binding globulin." — Saartok, Dahlberg & Gustafsson, Endocrinology (1984)

Practical outcome: dry, quality tissue — not water, not glycogen bloat. The on-paper 62:25 anabolic:androgenic rating understates real-world effect because it doesn't account for SHBG displacement (below).

No Aromatization — Zero Estrogen Conversion#

Because drostanolone is already 5α-reduced at the A-ring, it is not a substrate for CYP19 aromatase and cannot convert to estradiol. This is the structural reason Mast runs "dry" — no estrogen-driven water retention, no gyno risk from the compound itself, no E2-driven fat storage patterns.

"As a 5α-reduced derivative, drostanolone is not a substrate for aromatase and thus cannot be converted to estrogens." — Labrie et al., J Steroid Biochem Mol Biol (2005)

Practical outcome: Mast contributes zero estrogenic load to a stack. You still need to manage E2 from any aromatizing compound running alongside it (test, dbol), but Mast itself is estrogen-neutral.

Weak Aromatase Inhibition and Anti-Estrogen Activity#

Drostanolone was originally marketed (as Drolban / Masteril) as an adjuvant in metastatic breast cancer — not because it was cytotoxic, but because DHT-derivatives competitively occupy aromatase and reduce estradiol substrate turnover. The effect is weaker than a dedicated AI like anastrozole but is real and additive on cycle.

"Patients received drostanolone propionate 100 mg intramuscularly three times weekly for extended periods with observation of pharmacological and clinical effects." — Goldenberg, Cancer (1970)

Practical outcome: on moderate aromatizing stacks (test + deca, test + EQ), 300–400 mg/wk Mast often eliminates the need for an AI entirely in users who aren't gyno-prone. On high-aromatizing stacks (heavy test + dbol), it takes the edge off but doesn't replace anastrozole.

SHBG Binding and Free-Testosterone Lift#

DHT-scaffold compounds bind sex hormone-binding globulin with high affinity and effectively displace testosterone from its SHBG reservoir, raising the free fraction of co-administered test.

"DHT derivatives such as drostanolone exhibited strong binding to testosterone-binding globulin, potentially influencing the free fractions of other androgens." — Pugeat, Dunn & Nisula, J Clin Endocrinol Metab (1981)

Practical outcome: this is the mechanism behind the "grainy, 3D" hardening effect users chase pre-contest, and why libido typically stays elevated on a test + Mast cruise. More free test = more bioavailable androgen signal at muscle AR, independent of the Mast dose itself.

Metabolism and Hepatic Profile#

Drostanolone is cleared hepatically to 2α-methyl-5α-androstane-3α,17β-diol and related metabolites excreted in urine — the basis for WADA detection out to ~3 weeks (propionate) or ~3 months (enanthate).

"Drostanolone is metabolized primarily to 2α-methyl-5α-androstane-3α,17β-diol and related metabolites detectable in urine after injection." — Schänzer, Clinical Chemistry (1996)

Practical outcome: Mast is not 17α-alkylated, so hepatotoxicity is minimal at any realistic cycle dose — ALT/AST typically stay within range driven mostly by training, not the compound. The cardiovascular footprint (HDL suppression, hematocrit rise) is the real constraint, not the liver.

Common (most users)#

• Increased libido and aggression — usually welcome, but if it tips into irritability, reduce dose or reassess total androgen load (test + mast combined).
• Oily skin and mild acne — less than tren or high-dose test, more than primo. Keep a simple topical routine: benzoyl peroxide wash + adapalene. Don't bother with Accutane for cycle acne unless it's cystic.
• Scalp shedding / accelerated AGA — the big one. Drostanolone is a 2α-methyl DHT derivative with strong scalp AR affinity. Oral finasteride does not help (Mast is already 5α-reduced). Mitigation is topical AR antagonists — RU58841 50 mg/day or pyrilutamide — plus topical minoxidil. If your hairline is already receding hard, Mast is not the compound for you.
• Injection site pain (PIP) — common with Mast E above 150 mg/mL; Mast P at 100 mg/mL and high concentrations of long-ester Mast cause lingering soreness. Stick with 100 mg/mL preps and rotate sites (glutes, ventroglutes, delts, quads).
• Hardening / "dry" physique effect — expected, not a side effect per se, but users on a wet cycle can overshoot and end up flat. Back off 100 mg/wk if pumps die and joints get cranky.

Uncommon (dose-dependent or individual)#

• HDL suppression — DHT-derivatives hammer HDL harder than testosterone. Expect a 30–50% drop by week 8. Bloodwork at week 6 and week 12; if HDL drops below 25 mg/dL or ApoB climbs hard, cut dose or consider a low-dose rosuvastatin + citrus bergamot + aggressive cardio protocol.
• Hematocrit rise — on top of any test base. Pull CBC at week 6; donate a unit of whole blood every 8–10 weeks if HCT climbs above 52%. Hydration and daily cardio help but don't replace donation.
• Blood pressure elevation — secondary to hematocrit and possible mild mineralocorticoid effect. Daily home cuff readings beat quarterly clinic readings. Telmisartan 40–80 mg is the go-to on-cycle antihypertensive.
• Libido crash if run without sufficient test — Mast suppresses the HPTA but doesn't fully replace test androgenically. Users who try to "Mast-only" or cruise with Mast > test almost always end up with dead libido inside 3–4 weeks. Keep test ≥ mast.
• Prostate enlargement / urinary symptoms — higher risk over 40 or with pre-existing BPH. Pull PSA at baseline and week 12; low-dose tadalafil 5 mg daily helps both the prostate and on-cycle pump.
• SHBG crash — Mast binds SHBG avidly. Free-T from your test base will run hotter than the numbers suggest. Useful to know when interpreting bloods — don't panic if total-T-to-SHBG ratios look weird.

Rare but serious#

• Cardiac remodeling / LVH — years of continuous high-androgen cycling (not Mast-specific, but Mast contributes) drives concentric hypertrophy and diastolic dysfunction. Get an echo if you've been blasting for multiple years. Warning signs: reduced exercise tolerance, exertional dyspnea, palpitations at rest.
• Severe dyslipidemia / premature atherosclerosis — the plausible long-term killer. Not a cycle-ending acute event, but the cumulative HDL/ApoB exposure is real. A lipid panel twice a year is the floor.
• Virilization in female users — clitoral hypertrophy, voice deepening, hirsutism, menstrual disruption. Voice changes are not reversible. Discontinue immediately at the first sign.
• Severe PIP with abscess / sterile inflammation — rare with legitimate gear, more common with crashed or under-filtered UGL Mast E. Red streaking, systemic fever, or hardening lumps that worsen past day 5 = urgent care, not "wait it out."

Hard contraindications#

• Prostate cancer, active or in remission — Mast is a potent AR agonist; do not run it.
• Pre-existing prostate hypertrophy with urinary obstruction — don't add a DHT-derivative to this picture.
• Untreated hypertension (>140/90 resting) or untreated dyslipidemia — fix the baseline first, then cycle.
• Active conception attempts / pregnancy in partner's timeline — Mast suppresses spermatogenesis; pair with hCG if conception is on the horizon, or don't run it.
• Aggressive androgenic alopecia without a topical AR-antagonist plan — Mast will accelerate it, and oral 5-AR inhibitors won't save you.
• Pregnancy or possible pregnancy — teratogenic androgen exposure to a female fetus. Absolute contraindication.
• Women unwilling to accept irreversible voice changes as a possible outcome — the risk is real even at 50–100 mg/wk in susceptible individuals.

"Drostanolone demonstrated high relative binding affinity for the androgen receptor in both skeletal muscle and prostate, as well as strong affinity for sex hormone-binding globulin." — Saartok et al., Endocrinology 1984

Gender-specific & PCT notes#

Female users: hard ceiling of 100 mg/wk Mast P, split EOD, in 4–6 week blocks pre-contest. Stick to propionate — the enanthate ester's long washout means you can't abort fast if virilization shows up. Discontinue at the first hoarseness, clitoral sensitivity change, or unusual hair growth. Voice changes do not reverse.

PCT: Mast is HPTA-suppressive. If run on a blast (not a TRT cruise), standard SERM protocol starts once exogenous androgens have cleared — roughly 3 days after last Mast P pin, or 2 weeks after last Mast E pin (matched to your test ester timing). Clomid 50/50/25/25 or nolvadex 40/40/20/20 over 4 weeks, optionally with hCG 500 IU 2×/wk for the 2 weeks before SERM start to restart testicular function. No AI typically needed in PCT — Mast doesn't aromatize, and estrogen rebound isn't a Mast issue.

Hepatotoxicity is effectively a non-issue — drostanolone is not 17α-alkylated. Don't let that lull you into skipping bloodwork; the cardiovascular and lipid story is where this compound earns its monitoring.