Primobolan
Also known as: Primo, Metenolone, Methenolone, Primobolan Depot, Metenolone Enanthate
Anabolic Steroid | Lean Mass & Low Side Effect Profile
Overview
Primobolan (metenolone) is a dihydrotestosterone (DHT)-derived anabolic steroid that has been in clinical and performance use since the 1960s. It was originally marketed by Schering as Primobolan (oral acetate) and Primobolan Depot (injectable enanthate) for the treatment of muscle wasting diseases, malnutrition, and osteoporosis. Although it was once FDA-approved in the United States, it has since been discontinued from the US market and is primarily available through international pharmacies and underground production. Primobolan is widely considered one of the mildest and safest anabolic steroids in terms of side effect profile. It does not aromatize to estrogen, carries low androgenic activity relative to its anabolic effects (anabolic-to-androgenic ratio of approximately 88:44 compared to testosterone at 100:100), and the injectable form is not hepatotoxic. It gained legendary status in golden-era bodybuilding, with Arnold Schwarzenegger reportedly favoring it as part of his competition preparation. Primobolan is particularly valued for lean tissue preservation during caloric deficits, quality muscle gains without water retention, and its compatibility with longer cycle durations due to its mild nature. Its primary drawback is cost -- it is one of the most expensive anabolic steroids per milligram, and effective doses require relatively high volumes of oil for injection.
Key benefits
- Lean muscle mass preservation during caloric deficits with minimal water retention
- Does not aromatize to estrogen, eliminating estrogen-related side effects
- One of the mildest androgenic profiles among anabolic steroids, with reduced risk of acne, aggression, and prostate issues
- Injectable form is non-hepatotoxic, allowing extended cycle durations
- Strong anti-catabolic properties through glucocorticoid receptor modulation
- Immune-enhancing effects at moderate therapeutic doses
- Quality, keepable muscle gains without the bloated appearance common with aromatizing steroids
- Compatible with long cycle lengths (16-20 weeks) due to mild overall impact on health markers
Mechanism of action
Metenolone binds to the androgen receptor (AR) to promote nitrogen retention, protein synthesis, and anti-catabolic effects in skeletal muscle tissue. As a DHT derivative, it cannot be aromatized by the aromatase enzyme, meaning it produces no estrogenic metabolites and does not contribute to water retention, gynecomastia, or estrogen-mediated fat gain. Unlike testosterone, which is converted to the more potent DHT by 5-alpha reductase, metenolone is already a DHT derivative and undergoes no further activation in androgen-sensitive tissues, resulting in a relatively mild androgenic profile. Metenolone has a strong affinity for androgen receptors in muscle tissue and exerts significant anti-catabolic effects by reducing glucocorticoid receptor expression and inhibiting cortisol-mediated protein breakdown. This makes it particularly effective during caloric restriction, where it helps preserve lean tissue. It also enhances immune function at moderate doses, which was one of its original clinical applications in immunocompromised patients. The injectable enanthate form bypasses hepatic first-pass metabolism entirely, making it non-hepatotoxic. The oral acetate form, while possessing a 1-methyl modification that provides some degree of oral bioavailability, is not 17-alpha-alkylated in the traditional sense but still exerts measurable hepatic stress at sustained doses.
Molecular data
- Type
- DHT-derivative steroid (C20H30O2)
- Half-life
- ~10 days (enanthate)
Indications
What the research community uses this compound for, with self-reported effectiveness.
Body Composition
Clinical / Therapeutic
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 400-600 mg/week | 2x per week (split dose) | — |
| — | 600-800 mg/week | 2x per week (split dose) | — |
| — | 50-100 mg/week | 1x per week | — |
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 50-100 mg/day | Split into 2 doses daily (morning and evening) | — |
| — | 25-50 mg/day | Once or twice daily | — |
Protocol variations
Alternative cycling patterns reported in the literature and community.
Metenolone Enanthate (Primobolan Depot)
Metenolone enanthate is a long-acting injectable formulation with a half-life of approximately 10 days. It is the standard and strongly preferred form for both clinical and performance applications. The enanthate ester bypasses hepatic first-pass metabolism entirely, eliminating liver toxicity concerns and allowing for extended cycle durations of 12-20 weeks. Typical concentrations are 100 mg/mL, though some underground labs produce 200 mg/mL formulations.
Metenolone Acetate (Oral Primobolan)
Metenolone acetate is the oral formulation with a half-life of approximately 4 hours. It possesses a 1-methyl modification that provides partial oral bioavailability, but it is not 17-alpha-alkylated, making it less hepatotoxic than most oral anabolic steroids. However, sustained daily dosing does produce measurable liver enzyme elevations, and cycle lengths should be limited accordingly. Oral primobolan is considerably less potent milligram-for-milligram than the injectable form and is substantially more expensive per equivalent effect.
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Suppression of natural testosterone production (dose-dependent, less suppressive than many other anabolic steroids but still significant)
- Hair thinning or accelerated male pattern baldness (DHT derivative -- this is the most commonly reported side effect in susceptible individuals)
- Adverse lipid changes, particularly HDL suppression (moderate compared to other anabolic steroids)
- Mild acne or oily skin (less pronounced than testosterone or other androgens)
- Injection site discomfort from larger oil volumes required at performance doses
- Gradual decline in natural testosterone production requiring post-cycle therapy
Rare side effects
- Significant virilization in women at higher doses (voice deepening, hirsutism, clitoral enlargement)
- Hepatotoxicity from oral acetate form at sustained high doses
- Mood changes including irritability or low mood, particularly during discontinuation
- Reduced libido if run without adequate testosterone base
- LDL cholesterol elevation with prolonged use at high doses
- Cardiovascular strain with chronic supraphysiological use
Contraindications
- Prostate cancer (active or history of hormone-sensitive prostate cancer)
- Breast cancer in males or females
- Pregnancy or potential for pregnancy (teratogenic risk -- fetal virilization)
- Severe hepatic impairment (particularly relevant for oral acetate form)
- Known hypersensitivity to metenolone or formulation components
- Hypercalcemia
- 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
- Complete blood count with hematocrit: baseline, 6-8 weeks, then every 3 months
- Comprehensive lipid panel (total cholesterol, LDL, HDL, triglycerides): baseline and every 8 weeks -- HDL suppression is the primary lipid concern
- Liver function tests: baseline and every 4-6 weeks (especially important for oral acetate users)
- Estradiol (sensitive assay): periodic monitoring to ensure estrogen is not driven too low when combined with AI use
- PSA (prostate-specific antigen): baseline and every 6 months for men over 40
- Blood pressure: regular monitoring throughout use
References
Primary literature and clinical-trial data informing this entry.