Methenolone
In a randomized 26-person stroke-rehabilitation study, injected metenolone enanthate increased thigh-muscle cross-sectional area more than control over six weeks. A separate small study reported favorable strength changes, and Japan has an oral acetate medicine. These disease-specific results do not establish healthy physique benefit, and the oral label retains liver, androgenic, and interaction risks.
Anabolic-androgenic steroid
- Primobolan
- Acetate and enanthate differ
What is Primobolan, and are the tablets and injections interchangeable?
Methenolone, also spelled metenolone, is an anabolic-androgenic steroid. Oral acetate and injectable enanthate are different formulations.
Japan’s Primobolan 5 mg label describes the acetate tablet. The stroke-rehabilitation studies used enanthate injections. Neither provides a dosing or clearance rule for the other.
PMDA · oral acetate uses and risks
Japanese prescribing information
PMDA. Primobolan 5 mg prescribing information.
The oral acetate label lists osteoporosis, specified wasting conditions and aplastic anemia. It warns about liver dysfunction, jaundice, virilization, fluid retention, glucose changes and interactions with coumarin anticoagulants and corticosteroids.
The summary is translated from Japanese. This tablet label does not describe an injectable enanthate product.
Read the original sourceStroke rehabilitation · muscle area
Randomized controlled trial
American journal of physical medicine & rehabilitation. PMID 21173687.
In 26 stroke patients, six weeks of metenolone enanthate during rehabilitation increased thigh-muscle cross-sectional area more than control: 13.4% versus 3.3% on the affected side and 14.5% versus 5.2% on the unaffected side.
- Treatment
- 100 mg intramuscularly each week in the study.
The principal reported outcome was CT-measured muscle area, not independent living, walking or long-term safety.
Read the original sourceIs there human evidence for muscle effects?
Small stroke-rehabilitation studies tested injectable metenolone enanthate. One randomized 26-person trial measured larger increases in thigh-muscle cross-sectional area than control, but it did not test bodybuilding outcomes.
| Thigh muscle area | Metenolone | Control |
|---|---|---|
| Affected side | +13.4% | +3.3% |
| Unaffected side | +14.5% | +5.2% |
26 patients with hemiplegia after stroke. The measured endpoint was CT cross-sectional area.
Stroke rehabilitation · muscle area
Randomized controlled trial
American journal of physical medicine & rehabilitation. PMID 21173687.
In 26 stroke patients, six weeks of metenolone enanthate during rehabilitation increased thigh-muscle cross-sectional area more than control: 13.4% versus 3.3% on the affected side and 14.5% versus 5.2% on the unaffected side.
- Treatment
- 100 mg intramuscularly each week in the study.
The principal reported outcome was CT-measured muscle area, not independent living, walking or long-term safety.
Read the original sourceDid it improve actual strength?
A separate 25-person study measured strength and reported favorable changes, but allocation was not randomized and treatment was open label. The report does not establish a precise strength gain for a healthy trained person.
Stroke rehabilitation · strength study
Nonrandomized open-label controlled trial
The International journal of neuroscience. PMID 20707637.
A separate 25-patient study compared rehabilitation plus metenolone enanthate with rehabilitation alone. More tested strength conditions improved from baseline in the treated group.
Observer blinding does not remove nonrandomized allocation. Comparing the number of significant within-group tests is not a single between-group treatment-effect estimate.
Read the original sourceDoes “not 17-alpha-alkylated” mean liver-safe?
No. The oral label warns about liver dysfunction and jaundice, and a published case describes fatal liver failure after methenolone acetate.
The case involved a severely ill older patient and cannot establish frequency. The oral label independently warns about liver dysfunction and jaundice.
Methenolone acetate · fatal liver case
Case report
Annals of hematology. PMID 8334198.
A 75-year-old man with severe aplastic anemia developed marked transaminase elevation, liver failure and death after metenolone acetate. Autopsy findings were compatible with drug-induced injury; authors considered metenolone the most likely cause.
The patient had serious underlying disease and previous treatments. One report establishes a warning signal, not its frequency.
Read the original sourcePMDA · oral acetate uses and risks
Japanese prescribing information
PMDA. Primobolan 5 mg prescribing information.
The oral acetate label lists osteoporosis, specified wasting conditions and aplastic anemia. It warns about liver dysfunction, jaundice, virilization, fluid retention, glucose changes and interactions with coumarin anticoagulants and corticosteroids.
The summary is translated from Japanese. This tablet label does not describe an injectable enanthate product.
Read the original sourceWhat other effects are listed?
Virilization, voice changes, fluid retention and impaired glucose tolerance are listed concerns. Pregnancy and androgen-dependent cancer are contraindications. Liver tests and relevant symptoms require monitoring.
PMDA · oral acetate uses and risks
Japanese prescribing information
PMDA. Primobolan 5 mg prescribing information.
The oral acetate label lists osteoporosis, specified wasting conditions and aplastic anemia. It warns about liver dysfunction, jaundice, virilization, fluid retention, glucose changes and interactions with coumarin anticoagulants and corticosteroids.
The summary is translated from Japanese. This tablet label does not describe an injectable enanthate product.
Read the original sourceWhat can animal heart findings tell us?
The rat study raises a cardiac hazard question. It does not determine the incidence, severity or exposure threshold of cardiac injury in people.
Methenolone enanthate · rat heart study
Animal experiment
Experimental and toxicologic pathology : official journal of the Gesellschaft fur Toxikologische Pathologie. PMID 23280519.
A pubertal-rat experiment reported cardiac structural changes after metenolone enanthate.
Animal heart morphology cannot establish a safe human exposure or quantify human cardiac risk.
Read the original sourceWhat do the older medical studies establish?
The older studies examined cancer treatment and stroke rehabilitation, with mixed outcomes. None tested general recovery in healthy people.
The breast-cancer series reported remissions in eight of 41 evaluable patients. In a different randomized lymphoma study, adding high-dose metenolone during chemotherapy worsened anemia and thrombocytopenia.
Historical breast-cancer series
Uncontrolled clinical series
Acta radiologica: therapy, physics, biology. PMID 1224996.
Eight of 41 evaluable patients had objective remissions lasting more than three months; 43 had entered treatment with metenolone enanthate.
The abstract does not establish a randomized comparator. Historical cancer response does not establish cosmetic benefit.
Read the original sourceLymphoma chemotherapy · harm signal
Randomized clinical trial
La Nouvelle presse medicale. PMID 909754.
In 32 patients randomized during MOPP chemotherapy, high-dose metenolone increased hematologic toxicity, including anemia and thrombocytopenia, and reduced the chemotherapy doses that could be delivered.
An old, specific chemotherapy setting. It contradicts a blanket claim that anabolic treatment always protects blood-cell production.
Read the original sourceHow does the chemistry differ from common oral steroids?
Methenolone’s methyl group is at carbon 1, rather than the 17-alpha position used in several other oral anabolic steroids.
The carbon-1 methyl position does not establish cardiovascular or reproductive safety, and oral acetate and injected enanthate have different exposure profiles.
FDA substance registry · structure
Chemical identity record
FDA Global Substance Registration System.
The registered structure places the methyl modification at carbon 1. Methenolone is not a 17-alpha-alkylated steroid.
The chemical identity record contains no clinical safety comparison.
Read the original sourcePMDA · oral acetate uses and risks
Japanese prescribing information
PMDA. Primobolan 5 mg prescribing information.
The oral acetate label lists osteoporosis, specified wasting conditions and aplastic anemia. It warns about liver dysfunction, jaundice, virilization, fluid retention, glucose changes and interactions with coumarin anticoagulants and corticosteroids.
The summary is translated from Japanese. This tablet label does not describe an injectable enanthate product.
Read the original sourceWhat half-life can be assigned to Primobolan?
The cited sources do not establish a validated terminal human half-life for both formulations.
Oral absorption, release from an injection depot, and urinary metabolite detection are different processes. A urinary detection result does not show how long an injection remains active.
Human pharmacokinetics · formulation-specific limits
Product labels and primary clinical records
Product labels and primary clinical records for methenolone formulations.
The cited clinical records include oral product labeling and injectable rehabilitation and oncology studies. They do not establish a validated terminal human half-life for each formulation.
What do the tablet instructions say about other medicines?
The Japanese label cautions about coumarin anticoagulants such as warfarin and about corticosteroids. It also calls for attention to glucose tolerance and fluid retention.
These instructions apply to the specified oral medicine. They are not a safety assessment of an online injectable product or a mixed-drug regimen.
PMDA · oral acetate uses and risks
Japanese prescribing information
PMDA. Primobolan 5 mg prescribing information.
The oral acetate label lists osteoporosis, specified wasting conditions and aplastic anemia. It warns about liver dysfunction, jaundice, virilization, fluid retention, glucose changes and interactions with coumarin anticoagulants and corticosteroids.
The summary is translated from Japanese. This tablet label does not describe an injectable enanthate product.
Read the original sourceStudies and sources
PMDA · oral acetate uses and risks
Japanese prescribing information
PMDA. Primobolan 5 mg prescribing information.
The oral acetate label lists osteoporosis, specified wasting conditions and aplastic anemia. It warns about liver dysfunction, jaundice, virilization, fluid retention, glucose changes and interactions with coumarin anticoagulants and corticosteroids.
The summary is translated from Japanese. This tablet label does not describe an injectable enanthate product.
Read the original sourceStroke rehabilitation · muscle area
Randomized controlled trial
American journal of physical medicine & rehabilitation. PMID 21173687.
In 26 stroke patients, six weeks of metenolone enanthate during rehabilitation increased thigh-muscle cross-sectional area more than control: 13.4% versus 3.3% on the affected side and 14.5% versus 5.2% on the unaffected side.
- Treatment
- 100 mg intramuscularly each week in the study.
The principal reported outcome was CT-measured muscle area, not independent living, walking or long-term safety.
Read the original sourceStroke rehabilitation · strength study
Nonrandomized open-label controlled trial
The International journal of neuroscience. PMID 20707637.
A separate 25-patient study compared rehabilitation plus metenolone enanthate with rehabilitation alone. More tested strength conditions improved from baseline in the treated group.
Observer blinding does not remove nonrandomized allocation. Comparing the number of significant within-group tests is not a single between-group treatment-effect estimate.
Read the original sourceLymphoma chemotherapy · harm signal
Randomized clinical trial
La Nouvelle presse medicale. PMID 909754.
In 32 patients randomized during MOPP chemotherapy, high-dose metenolone increased hematologic toxicity, including anemia and thrombocytopenia, and reduced the chemotherapy doses that could be delivered.
An old, specific chemotherapy setting. It contradicts a blanket claim that anabolic treatment always protects blood-cell production.
Read the original sourceHistorical breast-cancer series
Uncontrolled clinical series
Acta radiologica: therapy, physics, biology. PMID 1224996.
Eight of 41 evaluable patients had objective remissions lasting more than three months; 43 had entered treatment with metenolone enanthate.
The abstract does not establish a randomized comparator. Historical cancer response does not establish cosmetic benefit.
Read the original sourceMethenolone acetate · fatal liver case
Case report
Annals of hematology. PMID 8334198.
A 75-year-old man with severe aplastic anemia developed marked transaminase elevation, liver failure and death after metenolone acetate. Autopsy findings were compatible with drug-induced injury; authors considered metenolone the most likely cause.
The patient had serious underlying disease and previous treatments. One report establishes a warning signal, not its frequency.
Read the original sourceMethenolone enanthate · rat heart study
Animal experiment
Experimental and toxicologic pathology : official journal of the Gesellschaft fur Toxikologische Pathologie. PMID 23280519.
A pubertal-rat experiment reported cardiac structural changes after metenolone enanthate.
Animal heart morphology cannot establish a safe human exposure or quantify human cardiac risk.
Read the original sourceFDA substance registry · structure
Chemical identity record
FDA Global Substance Registration System.
The registered structure places the methyl modification at carbon 1. Methenolone is not a 17-alpha-alkylated steroid.
The chemical identity record contains no clinical safety comparison.
Read the original sourceHuman pharmacokinetics · formulation-specific limits
Product labels and primary clinical records
Product labels and primary clinical records for methenolone formulations.
The cited clinical records include oral product labeling and injectable rehabilitation and oncology studies. They do not establish a validated terminal human half-life for each formulation.
Why is Methenolone in B tier?
B reflects small human rehabilitation studies and an approved oral medicine in Japan. The evidence includes greater thigh-muscle area in a stroke population but does not establish healthy physique benefit or long-term safety.