Masteron
Also known as: Mast, Drostanolone, Drostanolone Propionate, Drostanolone Enanthate, Mast P, Mast E
DHT-Derived Anabolic Steroid | Hardening & Anti-Estrogenic
Overview
Masteron (drostanolone) is a synthetic dihydrotestosterone (DHT)-derived anabolic-androgenic steroid originally developed and marketed as Masteril and Drostanolone Propionate for the treatment of inoperable breast cancer in postmenopausal women. It received FDA approval for this indication in the 1970s but has since been discontinued from pharmaceutical markets. Structurally, drostanolone is DHT with a 2-alpha-methyl group, which increases its anabolic potency and protects it from metabolic breakdown by 3-alpha-hydroxysteroid dehydrogenase in muscle tissue. As a DHT derivative, Masteron does not aromatize to estrogen and exhibits mild anti-estrogenic properties, likely through competitive inhibition at the aromatase enzyme or direct antagonism at the estrogen receptor. This makes it uniquely suited for cutting and contest preparation cycles where a dry, hard, and grainy physique is desired. Masteron is not a mass-building compound; its primary value lies in aesthetic enhancement, estrogen management, and synergy with other anabolic agents. It is available in two ester forms: the short-acting propionate (original pharmaceutical form) and the longer-acting enanthate (underground lab formulation). Effective results are most visible at lower body fat percentages, typically below 12-15%, where its hardening and drying effects become pronounced.
Key benefits
- Produces a hard, dry, and grainy appearance by eliminating subcutaneous water retention
- Mild anti-estrogenic properties that can reduce or replace the need for aromatase inhibitors on cycle
- Does not aromatize, eliminating estrogen-mediated side effects from the compound itself
- Enhances the visual effects of other steroids in a stack by reducing water retention and bloat
- Modest increases in strength without significant weight gain, useful for weight-class athletes
- Improves muscle density and vascularity at low body fat percentages
- Well-tolerated with a relatively mild side effect profile compared to other anabolic steroids
- Short detection window with propionate ester compared to many other injectable steroids
Mechanism of action
Drostanolone binds to the androgen receptor with high affinity, promoting protein synthesis and nitrogen retention in skeletal muscle. As a DHT derivative, it cannot be converted to estrogen by the aromatase enzyme, eliminating estrogen-related side effects such as water retention and gynecomastia from the compound itself. Masteron exhibits anti-estrogenic activity through a dual mechanism: it competitively inhibits aromatase enzyme activity (reducing conversion of other aromatizable steroids like testosterone to estradiol) and may act as a weak antagonist at estrogen receptors in breast tissue, which was the basis for its historical use in breast cancer treatment. This anti-estrogenic property is the reason Masteron can reduce or eliminate the need for dedicated aromatase inhibitors when stacked with testosterone. Unlike testosterone, drostanolone is not a substrate for 5-alpha reductase, as it is already a DHT derivative and cannot be further reduced. This means its full androgenic potency is expressed in all tissues, including hair follicles and the prostate, which accounts for its significant hair loss potential in genetically predisposed individuals. The 2-alpha-methyl modification prevents inactivation by 3-alpha-hydroxysteroid dehydrogenase in muscle, allowing drostanolone to exert its full anabolic effect at the tissue level rather than being rapidly metabolized to inactive forms as unmodified DHT would be.
Molecular data
- Type
- DHT-derived anabolic steroid (C20H32O2)
- Half-life
- ~2 days (propionate), ~10 days (enanthate)
Indications
What the research community uses this compound for, with self-reported effectiveness.
Oncology (Historical)
Body Composition
Hormonal Management
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 300-400 mg/week | Every other day (propionate) or 2x per week (enanthate) | — |
| — | 400-500 mg/week | Every other day or daily (propionate) | — |
| — | 200-300 mg/week | Every other day (propionate) or 2x per week (enanthate) | — |
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Hair loss and accelerated male pattern baldness (significant risk as a DHT derivative - the most commonly reported side effect)
- Acne and increased skin oiliness, particularly on the back and shoulders
- Suppression of natural testosterone production (requires PCT or ongoing TRT)
- Injection site pain or discomfort (more common with propionate ester)
- Mild aggression or irritability from elevated androgenic activity
- HDL cholesterol suppression and adverse lipid profile changes
Rare side effects
- Prostate enlargement or urinary symptoms in predisposed individuals
- Virilization in women (deepening voice, hirsutism, clitoral enlargement) even at low doses
- Insomnia or restlessness at higher doses
- Left ventricular hypertrophy with prolonged supraphysiological use
- Elevated hematocrit requiring monitoring at higher doses or prolonged use
- Mood changes including depressive symptoms during discontinuation
Contraindications
- Prostate cancer (active or history of hormone-sensitive prostate cancer)
- Breast cancer in males
- Pregnancy or potential for pregnancy (causes virilization of female fetus)
- Known hypersensitivity to drostanolone or any formulation components
- Severe hepatic impairment
- Pre-existing significant hair loss where further androgenic exposure is unacceptable
- Polycythemia (hematocrit above 54% at baseline)
- Uncontrolled cardiovascular disease or severe dyslipidemia
Monitoring
- Total and free testosterone: baseline and every 6-8 weeks during use
- Estradiol (sensitive assay): important to ensure adequate estrogen levels are maintained, as Masteron's anti-estrogenic effect combined with any AI use can crash estradiol
- Complete blood count with hematocrit: baseline, 6-8 weeks, then every 3 months
- Comprehensive metabolic panel and lipid panel: baseline and every 8-12 weeks (pay particular attention to HDL suppression)
- Liver function tests: baseline and periodic monitoring
- PSA (prostate-specific antigen): baseline and every 6 months for men over 40
- Blood pressure: regular monitoring throughout use
- Hair loss assessment: document baseline hair density if hair preservation is a concern
References
Primary literature and clinical-trial data informing this entry.