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Primobolan

Methenolone Enanthate · Primo

Primobolan is a brand name for methenolone, a synthetic anabolic-androgenic steroid (AAS) derived from dihydrotestosterone (DHT). It exists as an injectable ester (methenolone enanthate) and an oral form (methenolone acetate). Historically it was used medically to stimulate red-blood-cell production in bone-marrow-failure anemias (e.g., aplastic anemia); it has no current mainstream therapeutic role and is now used non-medically for muscle-building. It is often marketed as a "mild" or "safe" steroid, but this framing is misleading: like all AAS it suppresses the body's own testosterone production, and long-term AAS use is linked to serious cardiovascular harm (reduced heart-pumping function, accelerated coronary artery plaque, and case reports of heart attack in methenolone users). Because it raises red-cell mass, it can also thicken the blood. Methenolone-specific human safety data are thin: most evidence is old observational anemia studies, case reports, and extrapolation from the AAS class as a whole, so certainty about its risks is low, not reassuring. Anyone using or considering it should be under medical supervision with regular bloodwork.

Clinical readoutAAS · injectable-dht
Hepatic strainLow
CardiovascularHigh
HPTA suppressionVery high
Half-life
Not well characte…
Route
Intramuscular injection
Evidence
C
Active
Enanthate
1·t½2·t½3·t½4·t½5·t½
Illustrative single-compartment washout · each mark = one half-life · t½ ≈ Not well characterized in peer-reviewed human pharmacokinetic studies. The injectable enanthate ester is a slow-release intramuscular depot acting over a period of days; the oral acetate is short-acting and cleared within roughly a day, historically requiring frequent dosing. Precise validated elimination half-life values are not reliably established in the primary human literature.
Pharmacology

Mechanism of action

Methenolone (1-methyl-5α-androstan-1-en-17β-ol-3-one) is a 5α-reduced, DHT-derived androgen that binds the androgen receptor to promote nitrogen retention and protein synthesis in muscle and to stimulate erythropoiesis (red-cell production), which underlay its historical use in anemia. It is non-aromatizable (not converted to estrogen), so it does not directly produce estrogenic effects such as gynecomastia. It is not 17α-alkylated; oral activity of the acetate and depot action of the injectable enanthate come from the 1-methyl group and the fatty-acid ester, respectively, rather than 17α-alkylation. Like all exogenous androgens it signals negative feedback on the hypothalamic-pituitary-gonadal axis, suppressing LH/FSH and endogenous testosterone. Preclinical work in human adrenocortical cells shows methenolone can raise mineralocorticoid output, a proposed mechanism for hypertension.
Kinetics

Pharmacokinetics

Half-life

Not well characterized in peer-reviewed human pharmacokinetic studies. The injectable enanthate ester is a slow-release intramuscular depot acting over a period of days; the oral acetate is short-acting and cleared within roughly a day, historically requiring frequent dosing. Precise validated elimination half-life values are not reliably established in the primary human literature.

Active duration

Enanthate (injectable): prolonged over several days per injection due to slow ester hydrolysis; acetate (oral): short, on the order of hours, requiring repeated daily dosing.

Route

Intramuscular injection (methenolone enanthate) or oral (methenolone acetate).

Metabolism & clearance

Hepatic phase I/II metabolism to glucuronide and sulfate conjugates with renal excretion. In a controlled human administration study, urinary metabolites of metenolone were detectable for up to ~40 days after oral dosing; sulfate-conjugate metabolites extend the detection window further. These washout figures are relevant only for clinician monitoring and estimating how long the drug and its effects persist, not for evading testing.

For monitoring and washout planning, not drug-test evasion.

Reported effects

Physiological & performance effects

  • Historically used to stimulate erythropoiesis (red-cell production) in bone-marrow-failure anemias such as aplastic and hypoplastic anemia
  • Promotes nitrogen retention and skeletal-muscle protein synthesis (anabolic effect on muscle)
  • Comparatively low androgenic and anabolic potency relative to testosterone; non-aromatizable, so no direct estrogenic activity
  • Increases red-cell mass/hematocrit, a therapeutic effect in anemia but a risk factor for blood thickening when misused
Safety

Adverse effects by system

Cardiovascular

Highest-concern system. A case report describes acute myocardial infarction with angiographically normal coronary arteries in a 32-year-old man using methenolone acetate 200 mg/week for 3 years, and an autopsy series links long-term methenolone (with nandrolone) use to apoptotic myocardial fibrosis and fatal heart failure without atherosclerosis. At the AAS-class level, a controlled cohort of long-term users showed reduced left-ventricular systolic and diastolic function and accelerated, dose-dependent coronary atherosclerosis. Preclinical data suggest methenolone may raise mineralocorticoid production, a possible route to hypertension. Adverse lipid shifts are an expected androgen class effect.

Hepatic

Methenolone is not 17α-alkylated (injectable enanthate and oral acetate), so it is expected to carry lower hepatotoxic risk than 17α-alkylated oral steroids; no methenolone-specific human hepatotoxicity reports were identified. Hepatotoxicity is nonetheless a documented AAS class effect, and absence of methenolone-specific data is not proof of hepatic safety.

Endocrine / HPTA

Suppresses the hypothalamic-pituitary-gonadal axis, lowering LH/FSH and endogenous testosterone. After cessation, recovery of the axis is variable and can be prolonged or, in some individuals, incomplete.

Reproductive

Through HPG-axis suppression, methenolone can cause testicular atrophy, suppressed spermatogenesis, and impaired fertility; recovery of spermatogenesis after stopping is variable. In women, androgenic exposure can cause irreversible virilization.

Neuropsychiatric

No methenolone-specific human data identified. Class-level effects are idiosyncratic and affect a minority of users: supraphysiologic androgen exposure can cause irritability, aggression, and mood changes, and withdrawal can cause depression.

Renal

No methenolone-specific human data identified. Nephrotoxicity has been reported at the AAS class level with long-term androgen use.

Hematologic

Stimulates erythropoiesis and raises red-cell mass/hematocrit (the basis for its historical use in anemia), which when misused can produce erythrocytosis (blood thickening) and a theoretical increase in thrombotic risk.

Dermatologic

No methenolone-specific human dermatologic studies identified. As a DHT-derived androgen, androgenic skin/hair effects (acne, oily skin, accelerated male-pattern hair loss, and virilization/hirsutism in women) are mechanistically plausible; being non-aromatizable, it is not expected to cause estrogen-driven effects like gynecomastia.

Recovery

HPTA suppression & recovery

Suppression: Marked and expected: exogenous androgen suppresses LH/FSH and endogenous testosterone

Recovery of the hypothalamic-pituitary-gonadal axis after stopping is variable and individual: one observational study found ~80% of users met testosterone/LH recovery criteria by 3 months while ~20% did not, with poorer recovery linked to longer duration, higher dose, and steroid type (PMID 33351319); a systematic review found full documented recovery is often difficult and sometimes incomplete (PMID 33887077). Any recovery approach should be directed by an endocrinologist. Where pharmacologic assistance is described in the literature it involves single-agent selective estrogen receptor modulator or gonadotropin approaches used off-label (PMID 26908067); dual-SERM protocols are out of scope. This is not a recommendation to self-manage recovery.

Bloodwork & vitals

Monitoring

Recommended labs & checks
Complete blood count with hematocrit/hemoglobin (erythrocytosis surveillance)Fasting lipid panel (HDL/LDL)Blood pressureLiver function tests (AST, ALT, bilirubin)Total and free testosterone, LH, FSH (HPG-axis status)Renal function (creatinine, eGFR)Consider PSA and cardiovascular risk assessment/echocardiography in longer-term or higher-risk users

Cadence: Baseline before any use, then periodically during use (e.g., roughly every 8-12 weeks) and again after cessation to track HPG-axis recovery, with cadence set by a treating clinician.

Warning signs — seek care
  • Chest pain, breathlessness, palpitations, or exercise intolerance (seek emergency care)
  • Markedly rising hematocrit/hemoglobin or symptoms of blood thickening (headache, visual changes, flushing)
  • New or worsening high blood pressure
  • Leg swelling, one-sided limb pain/swelling, or signs of clot or heart failure
  • Jaundice, dark urine, right-upper-quadrant pain (liver injury)
  • Persistent low mood, aggression, or mood instability
  • Testicular shrinkage, loss of libido, or infertility; virilization in women
Do not use if

Contraindications

  • Known or suspected prostate or breast carcinoma (androgen-sensitive cancers)
  • Pregnancy and breastfeeding (androgen exposure causes fetal virilization)
  • Pre-existing cardiovascular disease, heart failure, or uncontrolled hypertension
  • Polycythemia / elevated hematocrit or other hyperviscosity/thrombotic risk states
  • Significant hepatic impairment
  • Untreated hyperlipidemia or high baseline cardiovascular risk
  • Use in women seeking to avoid virilization; use in adolescents (premature epiphyseal closure and endocrine disruption)
Combinations

Interaction profile

  • MajorWith another anabolic steroid: Additive cardiovascular strain
  • MajorWith a thermogenic stimulant: Additive cardiovascular strain
  • ModerateWith thyroid hormone: Additive cardiovascular strain
  • ModerateWith growth hormone: Additive cardiovascular strain
  • MajorWith another anabolic steroid: Blood / clotting
  • MajorWith a clot-promoting SERM: Blood / clotting
  • ModerateWith an aromatase inhibitor: Hormonal
  • ModerateWith an anabolic steroid: Hormonal
  • ContraindicatedWith DNP: Additive cardiovascular strain

Check a specific combination in the interaction checker.

Harm reduction

Reducing harm & when to stop

  • This is educational information, not medical advice, and not an endorsement of use; these substances carry serious risks and any use should be under a physician with regular bloodwork. 21+ only.
  • The 'mild/safe steroid' reputation is not supported by strong methenolone-specific human safety data: most evidence is old observational anemia use, case reports, and class-level extrapolation.
  • Because methenolone raises red-cell mass, monitor hematocrit/hemoglobin; a rising or high hematocrit signals blood thickening and increased clot risk, a reason to stop and seek medical care.
  • Cardiovascular risk is the primary concern: monitor blood pressure, lipids, and cardiac symptoms; chest pain or breathlessness warrants emergency evaluation even in young, otherwise healthy users.
  • It suppresses your own testosterone; recovery is variable and can be incomplete. Do not attempt to self-manage HPG-axis recovery; consult an endocrinologist.
  • Stop use and seek medical care for jaundice, dark urine, severe headache/visual changes, leg swelling or one-sided limb pain, persistent mood disturbance, or signs of heart strain.
  • Contraindicated with androgen-sensitive cancers, pregnancy/breastfeeding, and pre-existing cardiovascular disease; not for use in adolescents.
  • Get baseline bloodwork before any use and follow-up labs during and after, interpreted by a clinician.
Evidence

Citations (12)

Every clinical claim above is tied to a primary source. Overall evidence grade C — graded to the best available evidence for its core claims.

  1. 01

    Methenolone (with stanozolol and nandrolone) was used to treat aplastic anemia by stimulating erythropoiesis, in a series of 130 cases.

    CohortTreatment of aplastic anaemia with methenolone, stanozolol and nandrolone. A report of 130 cases.PMID 6179032 ↗

  2. 02

    Methenolone was used clinically as an anabolic agent in hematology to stimulate erythropoiesis in anemias.

    Case series[Anabolic drugs in hematology].PMID 5328427 ↗

  3. 03

    Chronic methenolone acetate use (200 mg/week for 3 years) was associated with acute myocardial infarction despite angiographically normal coronary arteries in a 32-year-old bodybuilder.

    Case reportChronic anabolic androgenic steroid usage associated with acute coronary syndrome in bodybuilder.PMID 27239638 ↗

  4. 04

    Long-term supratherapeutic methenolone (with nandrolone) use was associated with apoptotic myocardial fibrosis/remodeling and fatal heart failure in the absence of atherosclerosis, on autopsy immunohistochemistry.

    Case seriesVentricular androgenic-anabolic steroid-related remodeling: an immunohistochemical study.PMID 28432434 ↗

  5. 05

    Long-term AAS use is associated with reduced left-ventricular systolic and diastolic function and dose-dependent accelerated coronary atherosclerosis compared with non-users.

    CohortCardiovascular Toxicity of Illicit Anabolic-Androgenic Steroid UsePMID 28533317 ↗

  6. 06

    Methenolone increased mineralocorticoid production in human adrenocortical (H295R) cells, a proposed mechanism for promoting hypertension/cardiovascular disease (preclinical).

    PreclinicalProfiling of anabolic androgenic steroids and selective androgen receptor modulators for interference with adrenal steroidogenesis.PMID 31884045 ↗

  7. 07

    Long-term androgen (AAS) abuse produces cardiovascular toxicity, can cause prolonged or irreversible hypogonadism on withdrawal, idiosyncratic neuropsychiatric effects, and hepatotoxicity and nephrotoxicity.

    ReviewPublic health impact of androgens.PMID 29369918 ↗

  8. 08

    AAS-induced hypogonadism is frequently underestimated and full recovery of the HPG axis is often difficult and sometimes incomplete.

    ReviewAnabolic androgenic steroid-induced hypogonadism, a reversible condition in male individuals? A systematic review.PMID 33887077 ↗

  9. 09

    After stopping AAS, ~80% of users met testosterone/LH recovery criteria by 3 months while ~20% did not, with poorer recovery correlated to longer duration, higher dose, and steroid type.

    Cohort[Peculiarity of recovery of the hypothalamic-pituitary-gonadal (HPG) axis, in men after using androgenic anabolic steroids].PMID 33351319 ↗

  10. 10

    AAS suppress the HPG axis and diminish spermatogenesis; recovery after cessation is variable, and off-label single-agent SERM or gonadotropin approaches have been described for HPG/spermatogenesis recovery under specialist care.

    ReviewRecovery of spermatogenesis following testosterone replacement therapy or anabolic-androgenic steroid use.PMID 26908067 ↗

  11. 11

    Urinary metenolone metabolites were detectable for up to ~40 days after a controlled oral dose in a human volunteer (washout/monitoring reference).

    Case reportNew long term metabolite in human urine for metenolone misuse by liquid chromatography quadrupole time-of-flight mass spectrometry.PMID 26519767 ↗

  12. 12

    Sulfate-conjugated metenolone metabolites extend the urinary detection window relative to conventional markers (metabolism/washout reference).

    Case reportEnabling the inclusion of non-hydrolysed sulfated long term anabolic steroid metabolites in a screening for doping substances by means of gas chromatography quadrupole time-of-flight mass spectrometry.PMID 33735641 ↗

Last reviewed 2026-07-06 · Verified against PubMed · Educational, not medical advice