Metenolone acetate (also spelled methenolone acetate) is the short-chain acetate ester of metenolone, an anabolic-androgenic steroid built on the dihydrotestosterone (DHT) skeleton. It entered medical use in the early 1960s under the Primobolan name, and it is the form of metenolone that is taken by mouth. The long-acting injectable product, Primobolan Depot, is a different ester, metenolone enanthate.
The acetate is still a prescription drug in Japan, where Bayer sells Primobolan 5 mg tablets for osteoporosis, severe wasting and aplastic anemia (Japanese package insert). It has never been FDA-approved in the US, where it is a Schedule III controlled substance. Controlled human trials are few and mostly decades old, and none tested it for muscle gain in healthy people.
This page summarizes what the Japanese product label, the published studies and regulators report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Anabolic-androgenic steroid (androstane derivative), ATC code A14AA04 |
| Brand / authorization | Primobolan tablets 5 mg (Bayer Yakuhin, Japan), prescription-only |
| Route | Oral tablet; we found no current regulatory record of an injectable acetate product |
| Labeled adult dose (Japan) | 10–20 mg/day, split into 2–3 doses |
| Half-life | Not stated in the label; no published human half-life found |
| Metenolone content | ≈ 88% of the ester’s weight (5 mg tablet ≈ 4.4 mg metenolone) |
| 17α-methyl group | No (unlike most oral steroids) |
| US status | Not FDA-approved; Schedule III controlled substance |
| WADA status | Prohibited at all times (class S1.1, anabolic androgenic steroids) |
What it is
Metenolone is 1-methyl-17β-hydroxy-5α-androst-1-en-3-one (21 CFR 1308.13). Compared with DHT, it carries a double bond between carbons 1 and 2 and a methyl group at carbon 1. The acetate form adds a two-carbon acetic acid group to the 17β-hydroxyl. The Japanese label gives the chemical name as 1-methyl-3-oxo-5α-androst-1-en-17β-yl acetate.
The table compares the free steroid with its two marketed esters (PubChem, metenolone acetate; PubChem, metenolone; PubChem, metenolone enanthate):
| Form | Formula | Molecular weight | Share that is metenolone | Marketed as |
|---|---|---|---|---|
| Metenolone (free steroid) | C₂₀H₃₀O₂ | 302.5 g/mol | 100% | Not marketed |
| Metenolone acetate | C₂₂H₃₂O₃ | 344.5 g/mol | ≈ 88% | Oral tablets (Primobolan) |
| Metenolone enanthate | C₂₇H₄₂O₃ | 414.6 g/mol | ≈ 73% | Oil injection (Primobolan Depot) |
Most oral steroids, such as oxandrolone, carry a 17α-methyl group that slows breakdown in the liver. Metenolone acetate does not, yet it is labeled for oral use. For the injectable ester, see Primobolan (metenolone enanthate). The library’s oral Primobolan entry refers to the same tablet drug described on this page.
Some of the earliest papers on the acetate date from 1962: an animal study of growth and body composition with both esters (Joechle and Langecker, Arzneimittelforschung 1962) and a clinical report on oral dosing (Weller, Arzneimittelforschung 1962).
Receptor binding
Metenolone acts through the androgen receptor. In rat and rabbit tissue, its binding ranked below nandrolone but above testosterone, and it bound only weakly to sex hormone-binding globulin (SHBG), the blood protein that carries testosterone (Saartok et al., Endocrinology 1984). Binding in muscle and prostate was similar for most steroids tested, so receptor data do not show a muscle-selective steroid.
About “injectable Primobolan acetate.” Metenolone acetate is described in its current label as an oral drug, and the only metenolone product authorized in Spain, where Primobolan Depot is still sold, is the injectable enanthate (AEMPS CIMA). We found no current regulatory record of an injectable acetate, and no human pharmacokinetic study of one. Any injectable sold as “metenolone acetate” comes from outside the regulated drug supply.
Pharmacokinetics
The Japanese label gives only excretion data, from a 1960s study with a radiolabeled dose (Japanese package insert):
| Parameter | What the label states |
|---|---|
| Study | 4 healthy men, single oral dose of 114 mg ¹⁴C-metenolone acetate (above the approved 10–20 mg/day) |
| Urinary excretion | 21–47% of the dose within 7–13 days |
| Fecal excretion | 14–22% of the dose within 7–13 days |
| Half-life, peak level, time to peak | Not stated |
The label does not give an elimination half-life, and we found no published human study that measured one.
Metabolism and detection
After a 50 mg oral dose of metenolone acetate in two men, researchers identified twelve urinary metabolites (Goudreault and Massé, J Steroid Biochem Mol Biol 1990):
- The main metabolite was 3α-hydroxy-1-methylen-5α-androstan-17-one.
- Unchanged metenolone was detected in urine for up to 90 hours.
- It accounted for only 1.63% of the dose.
Detection windows have grown as methods improved:
| Study | Dose | Longest detection |
|---|---|---|
| Björkhem and Ek, J Steroid Biochem 1983 | Single oral 10 mg Primobolan | Main metabolite measurable for 5 days |
| Albertsdóttir et al., Drug Test Anal 2020 | Two excretion studies (form not stated in the abstract) | Sulfated metabolite up to 17 days |
| He et al., Steroids 2016 | One volunteer, oral metenolone | Sulfated metabolite up to 40 days |
Approved medical use
In Japan, Primobolan tablets are a prescription medicine with these labeled indications (Japanese package insert):
- osteoporosis;
- marked wasting caused by chronic kidney disease, cancer, trauma or burns;
- bone marrow depletion from aplastic anemia (a failure of the marrow to make blood cells).
The usual adult dose is 10–20 mg/day of metenolone acetate, split into 2–3 oral doses, adjusted for age and symptoms. The label says children should be treated with care because the drug can close growth plates early and cause precocious puberty.
In the US, a search of FDA’s Drugs@FDA data returned no metenolone product (openFDA). Metenolone, including its esters, is a Schedule III anabolic steroid (21 CFR 1308.13(f)).
What the research shows
Protein, mineral and blood effects in early studies
The Japanese label summarizes small 1960s studies in healthy people and in patients with osteoporosis, hypogonadism or muscle disease. They were not placebo-controlled:
| Measure | Dose | Reported effect |
|---|---|---|
| Nitrogen retention (a marker of protein build-up) | 20–30 mg/day, 330 mg in total | 47.1 mg/kg/day of nitrogen retained |
| Calcium and phosphorus retention | 20–30 mg/day, 300–360 mg in total | Calcium 1.26 mg/kg/day; phosphorus 2.75 mg/kg/day |
| Red cells | 20 mg/day for 28 days | Hemoglobin and red cell count increased |
Aplastic anemia
The best controlled data for oral metenolone come from aplastic anemia. In a randomized trial, 30 patients (18 with severe disease) received antithymocyte globulin (ATG), an immune-suppressing treatment, with or without oral metenolone at 3 mg/kg (Kaltwasser et al., Eur J Haematol 1988):
| Group | Patients | Responses | Survival |
|---|---|---|---|
| ATG + oral metenolone | 15 | 11 (8 complete, 3 partial) | 87% |
| ATG alone | 15 | 4 (2 complete, 2 partial) | 43% |
The difference in response was significant (p = 0.01), but the survival difference was not (p = 0.15). The authors noted that a controlled American study had found no benefit from adding androgens to ATG. The abstract does not name the ester, but metenolone’s oral form is the acetate. The 3 mg/kg dose is far above the 10–20 mg/day in the current label.
A 2024 case report described an older man with myelodysplastic syndrome and advanced kidney disease whose bone density loss slowed while he took metenolone acetate with darbepoetin for anemia (Ushimaru et al., JCEM Case Rep 2024). A single case cannot show cause and effect.
Osteoporosis
Osteoporosis is a labeled use in Japan, but the evidence base is thin. A 2008 Japanese review reported that anabolic steroids raised bone mineral content or density at the forearm and spine, that their use for osteoporosis had been declining, and that no prospective study had tested whether they prevent fractures (Adachi and Takayanagi, Clin Calcium 2008).
Muscle and performance
We found no controlled trial of metenolone acetate on muscle mass or strength in healthy or trained adults. The only modern controlled muscle data for metenolone come from small stroke-rehabilitation studies of the injectable enanthate, covered on the enanthate page.
Blood clotting
In men with ischemic heart disease, five 17α-alkylated oral steroids increased plasma fibrinolytic activity (the breakdown of blood clots), while metenolone acetate, the only non-alkylated steroid tested, did not (Walker et al., Thromb Diath Haemorrh 1975).
Side effects and risks
The Japanese label lists side effects without frequencies (Japanese package insert).
Liver
Lacking a 17α-methyl group does not make metenolone acetate free of liver risk:
- The label lists liver dysfunction with marked rises in AST, ALT and GGT (liver enzymes), and jaundice, as serious adverse reactions.
- It calls for regular liver tests, especially during long-term use.
- It notes reports of liver tumors in patients, such as those with aplastic anemia, who took anabolic steroids at high doses for long periods.
In one case report, a 75-year-old man with severe aplastic anemia developed sharply raised liver enzymes after starting metenolone acetate, then liver failure and death. Autopsy findings fit drug-induced liver injury, and metenolone acetate was judged the most likely cause (Tsukamoto et al., Ann Hematol 1993). The authors urged extreme caution in debilitated patients.
Virilization in women
The label tells prescribers to warn women about voice changes. Listed effects in women include:
- hoarseness, which can become hard to reverse as it progresses and is often preceded by menstrual changes;
- excess hair growth (hirsutism) and acne;
- skin pigmentation;
- menstrual abnormalities;
- clitoral enlargement and increased libido.
Effects in men and fertility
Listed effects in men include acne, penile enlargement, impotence and priapism (a prolonged, painful erection). The label states that large, continued doses suppress testicular function, with reduced sperm and semen. It also calls for regular prostate checks in men. No study has measured how much the acetate lowers LH, FSH or the body’s own testosterone at labeled doses.
Other cautions
The label advises care in people with:
- an enlarged prostate;
- heart or kidney disease, because of sodium and fluid retention;
- cancer that has spread to bone, because of the risk of high blood calcium;
- diabetes, because glucose tolerance can worsen;
- liver disease.
Nausea, vomiting and hypersensitivity reactions are also listed.
Interactions
- Corticosteroids: glucose tolerance may worsen when combined.
- Coumarin anticoagulants such as warfarin: their effect may be increased, so close monitoring is needed.
Who should not use it
The label lists two contraindications:
- androgen-dependent cancers, such as prostate cancer, or suspicion of one;
- pregnancy or possible pregnancy, because of the risk of virilizing a female fetus.
Legal status and use outside medicine
- US: Schedule III anabolic steroid, including its esters (21 CFR 1308.13(f)). No FDA-approved product exists.
- Sport: metenolone is named under S1.1 (anabolic androgenic steroids) on the 2026 list and is prohibited in and out of competition (WADA 2026 Prohibited List).
- Food residues: in an experiment, none of the men who ate chickens fed metenolone acetate (1 mg/day for 21 days) tested positive, while 50% of urine samples taken 24 hours after eating chickens injected with the depot ester were positive (Kicman et al., Clin Chem 1994).
Key takeaways
- The oral Primobolan. Metenolone acetate is the tablet form of metenolone, about 88% metenolone by weight. The injectable Primobolan Depot is the enanthate ester.
- Still approved in Japan. Labeled for osteoporosis, severe wasting and aplastic anemia at 10–20 mg/day in 2–3 divided doses. It is not FDA-approved and is Schedule III in the US.
- No published human half-life. The label gives only excretion data, and metabolites can be detected in urine for weeks with modern methods.
- Thin controlled evidence. The strongest trial is a 30-patient aplastic anemia study. No controlled trial has tested it for muscle in healthy adults, and none has shown fewer osteoporotic fractures.
- Not liver-safe by default. Despite lacking a 17α-methyl group, its label lists serious liver injury and jaundice, and a fatal case has been reported.
- Banned in sport. Prohibited at all times under WADA class S1.1.
Sources
- Bayer Yakuhin. Primobolan tablets 5 mg (metenolone acetate) package insert [in Japanese], revised August 2020 (1st edition). KEGG MEDICUS.
- Electronic Code of Federal Regulations. 21 CFR 1308.13, Schedule III, paragraph (f) Anabolic steroids. eCFR.
- US Food and Drug Administration. Drugs@FDA dataset, search for active ingredient methenolone. openFDA.
- Agencia Española de Medicamentos y Productos Sanitarios (AEMPS). CIMA registry search for active ingredient metenolona. AEMPS CIMA.
- World Anti-Doping Agency. The 2026 Prohibited List, International Standard. In effect January 1, 2026. WADA 2026 Prohibited List.
- National Center for Biotechnology Information. PubChem Compound Summary: methenolone acetate (CID 252372). PubChem.
- National Center for Biotechnology Information. PubChem Compound Summary: methenolone (CID 3037705). PubChem.
- National Center for Biotechnology Information. PubChem Compound Summary: metenolone enanthate (CID 248271). PubChem.
- Joechle W, Langecker H. Biological effects of 1-methyl-delta1-androsten-17beta-ol-3-one 17-acetate and 17-enanthate (methenolone acetate and methenolone enanthate): growth stimulation, composition of animal body and enzyme metabolism [in German]. Arzneimittelforschung. 1962;12:218–223. PubMed.
- Weller O. Clinical research with orally administered methenolone acetate [in German]. Arzneimittelforschung. 1962;12:234–240. PubMed.
- Saartok T, Dahlberg E, Gustafsson JA. Relative binding affinity of anabolic-androgenic steroids: comparison of the binding to the androgen receptors in skeletal muscle and in prostate, as well as to sex hormone-binding globulin. Endocrinology. 1984;114(6):2100–2106. PubMed.
- Goudreault D, Massé R. Studies on anabolic steroids–4. Identification of new urinary metabolites of methenolone acetate (Primobolan) in human by gas chromatography/mass spectrometry. J Steroid Biochem Mol Biol. 1990;37(1):137–154. PubMed.
- Björkhem I, Ek H. Detection and quantitation of 3 alpha-hydroxy-1-methylen-5 alpha-androstan-17-one, the major urinary metabolite of methenolone acetate (Primobolan) by isotope dilution–mass spectrometry. J Steroid Biochem. 1983;18(4):481–487. PubMed.
- Albertsdóttir AD, Van Gansbeke W, Coppieters G, et al. Searching for new long-term urinary metabolites of metenolone and drostanolone using gas chromatography-mass spectrometry with a focus on non-hydrolysed sulfates. Drug Test Anal. 2020;12(8):1041–1053. PubMed.
- He G, Yang S, Lu J, Xu Y. New long term metabolite in human urine for metenolone misuse by liquid chromatography quadrupole time-of-flight mass spectrometry. Steroids. 2016;105:1–11. PubMed.
- Kaltwasser JP, Dix U, Schalk KP, Vogt H. Effect of androgens on the response to antithymocyte globulin in patients with aplastic anaemia. Eur J Haematol. 1988;40(2):111–118. PubMed.
- Ushimaru S, Sumi H, Aso M, et al. Attenuation of bone mineral density decline during anemia treatment with methenolone acetate in myelodysplastic syndrome. JCEM Case Rep. 2024;2(4):luae055. PubMed.
- Adachi M, Takayanagi R. Effect of anabolic steroids on osteoporosis [in Japanese]. Clin Calcium. 2008;18(10):1451–1459. PubMed.
- Walker ID, Davidson JF, Young P, Conkie JA. Plasma fibrinolytic activity following oral anabolic steroid therapy. Thromb Diath Haemorrh. 1975;34(1):236–245. PubMed.
- Tsukamoto N, Uchiyama T, Takeuchi T, et al. Fatal outcome of a patient with severe aplastic anemia after treatment with metenolone acetate. Ann Hematol. 1993;67(1):41–43. PubMed.
- Kicman AT, Cowan DA, Myhre L, et al. Effect on sports drug tests of ingesting meat from steroid (methenolone)-treated livestock. Clin Chem. 1994;40(11 Pt 1):2084–2087. PubMed.