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
Lean Mass Preservation During Caloric Deficit
Most effectivePrimobolan's primary strength lies in its anti-catabolic properties during energy restriction. It significantly reduces muscle protein breakdown by modulating glucocorticoid receptor activity, making it a preferred compound for contest preparation and body recomposition phases where preserving lean tissue while losing fat is the primary objective.
Lean Mass Accretion
ModeratePrimobolan produces moderate but high-quality muscle gains without water retention. Gains are slower and less dramatic than with more potent anabolic steroids but are more easily retained after discontinuation. Milligram-for-milligram it is less potent than testosterone, nandrolone, or trenbolone for mass building.
Body Recomposition
EffectiveThe combination of anti-catabolic effects, zero aromatization, and moderate anabolic activity makes primobolan well-suited for simultaneous fat loss and lean tissue maintenance or modest gain, particularly when combined with a testosterone base.
Clinical / Therapeutic
Muscle Wasting and Cachexia
EffectiveOriginally prescribed for muscle wasting conditions, sarcopenia, and post-surgical recovery. Metenolone's mild side effect profile made it suitable for debilitated patients, including women and children, at conservative therapeutic doses.
Osteoporosis
ModerateHistorical clinical application for bone mineral density preservation, particularly in postmenopausal women. Its non-aromatizing nature and low androgenic activity made it a more tolerable option than other anabolic steroids for female patients.
Immune Support
ModerateMetenolone was used clinically to support immune function in immunocompromised patients, including those with AIDS-related wasting. It has demonstrated the ability to enhance T-cell counts and immune competence at moderate doses.
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Injectable
Primobolan Depot (metenolone enanthate) is administered via intramuscular injection. The enanthate ester provides a half-life of approximately 10 days, allowing for once or twice weekly injection schedules. The injectable form is not hepatotoxic and is the strongly preferred route of administration for both efficacy and safety. Due to metenolone's relatively low potency per milligram, effective performance doses require injecting larger volumes of oil (typically 2-4 mL per injection at standard 100 mg/mL concentration), which is a practical consideration.
| Protocol | Dose | Frequency | Route / duration |
|---|---|---|---|
| Lean Mass Preservation - Cutting Most common performance dosing range for cutting and recomposition. Run alongside a testosterone base at 1:1 ratio. Cycle length 12-16 weeks. No aromatase inhibitor typically needed due to zero aromatization from primobolan itself. | 400-600 mg/week | 2x per week (split dose) | Intramuscular |
| Lean Bulking Higher doses for lean tissue accrual. Often combined with testosterone at a 1:1 ratio (e.g., 600 mg primo / 600 mg test per week). Expect moderate, quality gains without water retention. Cycle length 16-20 weeks to capitalize on primobolan's gradual effects. | 600-800 mg/week | 2x per week (split dose) | Intramuscular |
| Female Protocol Primobolan is one of the better-tolerated anabolic steroids for women due to its low androgenic activity. Virilization risk is dose-dependent and lower than with most other injectable steroids. Monitor closely for voice changes, hirsutism, or other virilizing signs. | 50-100 mg/week | 1x per week | Intramuscular |
Preparation
You will need
- Pre-filled metenolone enanthate vial (typically 100 mg/mL in sesame or grape seed oil)
- Syringes (3 mL preferred due to larger injection volumes)
- Drawing needle (18-21 gauge)
- Injection needle (22-25 gauge for IM)
- Alcohol swabs
- Sharps container
Steps
- Wash hands thoroughly and prepare a clean work surface
- Wipe vial stopper with alcohol swab and allow to dry
- Draw air into syringe equal to the volume of oil to be withdrawn
- Insert drawing needle through vial stopper and inject air to equalize pressure
- Invert vial and withdraw the prescribed dose, tapping to remove air bubbles
- Switch to injection needle (do not inject with drawing needle)
- Clean injection site with alcohol swab in circular motion outward
- Insert needle at 90-degree angle into ventrogluteal, vastus lateralis, or deltoid muscle
- Aspirate briefly (optional per current guidelines), then inject slowly over 15-30 seconds
- Withdraw needle, apply gentle pressure with gauze, dispose of needle in sharps container
Work out the water volume and syringe units in the reconstitution calculator →
Oral
Primobolan tablets (metenolone acetate) provide an oral route of administration with a short half-life of approximately 4 hours. Unlike the injectable form, oral primobolan does exert hepatic stress, though it is not 17-alpha-alkylated and is considered less hepatotoxic than most oral steroids. Oral bioavailability is relatively low, requiring higher doses to achieve comparable effects to the injectable form. The oral form is significantly more expensive per effective dose and is less commonly used in performance settings.
| Protocol | Dose | Frequency | Route / duration |
|---|---|---|---|
| Cutting / Lean Mass Support Oral primobolan is less efficient than injectable. Cycle length should be limited to 6-8 weeks due to hepatic stress. Always run alongside a testosterone base. Daily cost is substantially higher than injectable per equivalent effect. | 50-100 mg/day | Split into 2 doses daily (morning and evening) | Oral |
| Female Protocol - Oral Lower doses for women to minimize virilization risk. The short half-life of the oral form allows rapid dose adjustment or discontinuation if virilizing side effects appear, which is an advantage over the long-acting injectable ester. | 25-50 mg/day | Once or twice daily | Oral |
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.
Interactions
Pairwise interactions with other compounds you might be cycling — the same data behind the cycle builder's safety check.
Testosterone
SynergisticTestosterone is the standard base compound run alongside primobolan. A 1:1 ratio (e.g., 500 mg test / 500 mg primo per week) is the most common approach. Testosterone provides the androgenic and estrogenic signaling that primobolan lacks, maintaining libido, mood, joint lubrication, and cardiovascular-protective estrogen levels. Some users run testosterone at a lower dose and rely on primobolan's non-aromatizing nature to keep overall estrogen lower during cutting phases.
Anastrozole
CompatibleAromatase inhibitors are compatible but typically unnecessary when primobolan makes up a significant portion of the total steroid load, since primobolan itself does not aromatize. AI use is dictated entirely by the testosterone dose in the stack. Some users find they can run higher testosterone doses alongside primobolan without needing an AI compared to testosterone alone, as the overall estrogen-to-androgen ratio remains favorable.
Growth Hormone
SynergisticGrowth hormone and primobolan are frequently combined for body recomposition and contest preparation. GH enhances fat mobilization and IGF-1-mediated anabolism while primobolan preserves lean tissue and provides anti-catabolic effects. The combination produces a lean, dry appearance prized in physique sports without the water retention associated with aromatizing steroids.
Timeline
Typical week-by-week effects reported in clinical and observational data.
- Week 1-3
Minimal noticeable effects with the enanthate ester as blood levels are still building toward steady state. Some users report a subtle improvement in mood and well-being. No significant changes in body composition or strength yet. Oral acetate users may notice mild effects sooner due to faster onset.
- Week 4-6
Blood levels approaching steady state. Early improvements in muscle hardness and fullness become apparent without accompanying water retention. Recovery between training sessions begins to improve. Strength may increase modestly. The visual quality of the physique starts to improve, particularly in leaner individuals.
- Week 7-10
Primary effects are well-established. Notable improvements in lean tissue preservation during caloric deficit, improved muscle density and separation, and enhanced recovery. Anti-catabolic effects are evident in sustained strength despite caloric restriction. Skin and complexion may appear clearer compared to aromatizing compounds.
- Week 11-16
Full cumulative benefits. Continued lean mass gains or preservation depending on dietary context. Body composition improvements are clearly visible. Lipid panel may show moderate HDL suppression -- bloodwork monitoring is recommended. For longer cycles, some users extend to 20 weeks given primobolan's mild impact on health markers.
- Post-Cycle (Week 16+)
Gains from primobolan are generally well-retained compared to compounds that produce water retention-based weight. The enanthate ester takes approximately 4-5 weeks to fully clear the system, so natural testosterone recovery is delayed accordingly. PCT should begin approximately 2 weeks after the last injection.
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
Stop signs — stop and seek advice
- Severe chest pain, tightness, or pressure
- Sudden shortness of breath or difficulty breathing at rest
- Yellowing of skin or eyes (jaundice) -- particularly with oral acetate
- Signs of stroke: sudden numbness, confusion, trouble speaking, loss of coordination
- Severe or persistent headaches with visual disturbances
- Rapid or unexplained hair loss beyond gradual thinning
- Women: rapid onset of voice deepening, significant facial hair growth, or menstrual cessation
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
Quality checks
What a legitimate product looks like, what should give pause, and what should make you stop.
Good signs
- Clear, pale yellow oil with no visible particles or cloudiness
- Pharmaceutical-grade product with valid lot number and manufacturer identification (e.g., Bayer Primobolan Depot)
- Proper labeling with concentration (typically 100 mg/mL), ester type (enanthate), and expiration date
- Intact rubber stopper and tamper-evident seal
- Oil draws smoothly with appropriate viscosity
- Consistent with known pharmaceutical packaging for the stated manufacturer
Warning signs
- Underground lab product -- primobolan is one of the most frequently counterfeited steroids due to high raw material cost
- Concentration claims above 200 mg/mL (metenolone enanthate has limited solubility at higher concentrations)
- Price significantly below market rate (genuine primobolan is expensive; cheap product is likely substituted with another steroid)
- Oral tablets without pharmaceutical branding (high counterfeit rate for oral primo)
- Vial label with spelling errors, misaligned printing, or unprofessional appearance
Stop signs — don't use
- Cloudy, discolored, or particulate-containing solution (contamination risk)
- Crashed product (crystallized steroid visible in vial)
- Broken or missing tamper-evident seal on vial or tablet blister pack
- No labeling, incorrect labeling, or missing expiration date
- Product testing reveals a different compound (common substitutions include boldenone undecylenate or testosterone)
- Severe post-injection pain, redness, or swelling lasting more than 72 hours
Recent research
Newer papers and trial readouts on file for this compound, with source and date.
January 2017 · Circulation: Heart Failure
Cardiovascular Effects of Anabolic Steroids: Cross-Sectional Study of Male Strength Athletes
Cross-sectional study of experienced strength athletes finding that long-term anabolic steroid use was associated with reduced left ventricular systolic function and coronary artery plaque volume, reinforcing the importance of cardiovascular monitoring even with milder compounds like primobolan.
March 2021 · Frontiers in Pharmacology
Anabolic Androgenic Steroids: Searching New Molecular Biomarkers
Review of emerging molecular biomarkers for detecting anabolic steroid use and monitoring health impacts. Highlighted the prolonged detection window of metenolone metabolites and the need for improved biomarker panels to assess subclinical organ damage from chronic anabolic steroid use.
June 2022 · Translational Andrology and Urology
Impact of anabolic androgenic steroids on sexual function
Review examining how various anabolic steroids impact sexual function, with particular attention to HPT axis suppression. Found that DHT derivatives like metenolone, while less likely to cause progestogenic sexual dysfunction compared to 19-nortestosterones, still significantly suppress endogenous testosterone and require a testosterone base for maintained sexual health.
References
Primary literature and clinical-trial data informing this entry.
Methyltestosterone, related steroids, and liver function
Westaby, D., Ogle, S.J., Paradinas, F.J., et al. · British Medical Journal · 1977
Early clinical documentation of the hepatic effects of various oral anabolic steroids, including metenolone acetate. Found that metenolone acetate, while not 17-alpha-alkylated, could produce mild liver enzyme elevations at sustained therapeutic doses, distinguishing it from the non-hepatotoxic injectable enanthate form.
Comparative androgenic, myotrophic and antigonadotrophic properties of some anabolic steroids
Potts, G.O., Arnold, A., Beyler, A.L. · Endocrinology · 1976
Established the anabolic-to-androgenic ratio of metenolone and other anabolic steroids in animal models. Demonstrated metenolone's favorable separation of anabolic and androgenic activity, supporting its clinical use in populations where androgenic side effects are undesirable.
The Effects of Supraphysiologic Doses of Testosterone on Muscle Size and Strength in Normal Men
Bhasin, S., Storer, T.W., Berman, N., et al. · The New England Journal of Medicine · 1996
Landmark study establishing dose-dependent anabolic effects of supraphysiological androgens on muscle size and strength. While focused on testosterone, this trial provided the foundational framework for understanding anabolic steroid dose-response relationships applicable to DHT derivatives including metenolone.
Anabolic steroid abuse and cardiac death
Fineschi, V., Riezzo, I., Centini, F., et al. · International Journal of Legal Medicine · 2007
Review of cardiovascular risks associated with anabolic steroid abuse. Documented that while milder compounds like metenolone carry lower cardiovascular risk per dose than more potent androgens, chronic supraphysiological use of any anabolic steroid poses risks including adverse lipid changes, left ventricular hypertrophy, and sudden cardiac events.
Last updated . How this page was sourced is described in the methodology.