History

Methenolone was introduced for medical use in the early 1960s and is commonly attributed to Schering; the injectable enanthate appeared around 1962, marketed in the US as Nibal/Nibal Depot (later withdrawn) and in Europe as Primobolan/Primobolan Depot. Its main approved indication was anemia due to bone marrow failure (aplastic and refractory anemias), and it was also studied in advanced breast carcinoma. It is now discontinued in most markets, remaining medically available in only a few countries (e.g., Spain, Turkey), with no current FDA-approved product in the US — most material in circulation today is illicit.

Methenolone (brand name Primobolan) is a synthetic anabolic-androgenic steroid derived from dihydrotestosterone (DHT). It is an androgen, not a peptide. Its genuine medical history is narrow — old, small studies in bone-marrow-failure anemias and a historical role in advanced breast cancer — while its modern fame comes almost entirely from bodybuilding culture, where it is marketed as a “mild” lean-tissue-preserving compound. That reputation is relative and partly mythologized: methenolone carries low liver toxicity and does not aromatize, but it remains a suppressive, virilizing androgen with cardiovascular and endocrine risks, and there is no high-quality modern trial evidence for its physique or performance claims.

What it is

Methenolone (INN: metenolone) is a DHT-derived anabolic-androgenic steroid, chemically 1-methyl-5α-androst-1-en-17β-ol-3-one (1-methyl-δ¹-DHT). The added C1–C2 double bond and 1-methyl group reduce inactivation by 3α-hydroxysteroid dehydrogenase and confer some oral bioavailability. It acts as a direct agonist of the androgen receptor and is generally described as having moderate anabolic and weak androgenic activity. It is not aromatized to estrogen (low intrinsic estrogenic potential) and has very low affinity for SHBG.

A key chemistry nuance: methenolone is not 17α-alkylated. Its oral form is active via 1-methylation rather than C17α-alkylation, which is why it is regarded as carrying low hepatotoxic potential relative to true 17α-alkylated orals (e.g., methyltestosterone, stanozolol, oxymetholone). It is supplied as two esters/prodrugs: metenolone acetate (oral; brands Primobolan, Nibal) and metenolone enanthate (intramuscular depot; brands Primobolan Depot, Nibal Injection).

The claims

Medical (historical/approved): treatment of anemia due to bone marrow failure (aplastic and refractory anemias), with secondary historical study in advanced breast carcinoma and exploration in wasting/catabolic states.
Physique/performance (off-label): that methenolone is a “mild and safe” anabolic that preserves or builds lean muscle without the harshness of other steroids — promoted as low-toxicity because it is non-aromatizing and not liver-toxic.

This profile reports no doses, cycles, ester schedules, or post-cycle protocols. It is a reference, not a how-to.

What the evidence actually shows

Aplastic / refractory anemia (its real medical niche). Kaltwasser et al. (1988), a prospective randomized trial in 30 aplastic anemia patients, found antithymocyte globulin (ATG) plus oral methenolone produced a 73% response (11/15) versus 27% (4/15) with ATG alone (p = 0.01); a survival advantage (87% vs 43%) did not reach significance (p = 0.15). The authors themselves acknowledged contradictory negative American studies, so the androgen benefit in aplastic anemia is not uniformly established. Lockner (1979) reported only modest, variable remission rates across refractory-anemia subtypes in 19 patients, with no clear survival prolongation even among responders (side effects described as negligible). Palva & Wasastjerna (1972) and older case series report partial remissions. Overall the anemia evidence is low-quality, old, and mixed, predating modern immunosuppressive and stem-cell standards of care.

Breast cancer. Kennedy & Yarbro (1968) reported objective improvement in roughly 48% of 27 postmenopausal women with advanced breast carcinoma treated with methenolone enanthate (with no improvement among 13 patients on testosterone propionate). This is historical and not part of modern oncology practice. The 48% figure is drawn from secondary summaries; the PubMed record itself carries no abstract.

Lean mass / strength / bodybuilding use. There are no rigorous modern randomized controlled trials demonstrating methenolone’s effects on lean mass or strength in healthy athletes. Its reputation as a “mild” lean-tissue-preserving anabolic comes from its DHT-derived, non-aromatizing profile and bodybuilding lore — not from controlled human performance trials. Generic AAS-class data (supraphysiologic androgens increase lean mass) do not specifically validate methenolone’s marketed claims, and claims of large strength/mass gains are not supported by high-quality evidence specific to this compound.

The net picture: a thin, dated human evidence base confined to anemia and historical breast cancer, with no robust modern evidence for the performance and physique uses that drive its popularity today.

Legal and regulatory status

In the United States, anabolic steroids are Schedule III controlled substances under the Anabolic Steroid Control Act (1990, amended by the Anabolic Steroid Control Act of 2004, effective Jan 20, 2005), within the Controlled Substances Act. Methenolone is specifically named within the federal definition of “anabolic steroid” — at 21 CFR 1300.01 (mirroring 21 USC 802(41)) — as “1-methyl-17β-hydroxy-5α-androst-1-en-3-one” (methenolone). The Schedule III placement of anabolic steroids as a class appears at 21 CFR 1308.13(f). There is no FDA-approved methenolone product in the US, and non-prescribed possession, distribution, or manufacture is a federal offense.

In sport, anabolic-androgenic steroids fall under WADA’s Class S1 (Anabolic Agents) and are prohibited at all times (in- and out-of-competition); within S1, exogenous AAS such as metenolone sit in S1.1a. Esters of prohibited anabolic agents are also banned, so both metenolone acetate and enanthate are prohibited. For context: clenbuterol is likewise an S1 anabolic agent banned at all times (no threshold), while growth hormone and hCG are prohibited under the separate S2 category (Peptide Hormones, Growth Factors, Related Substances and Mimetics).

Safety

Hepatotoxicity: Because methenolone is not 17α-alkylated, it is considered to carry low risk of the cholestatic/hepatocellular liver injury (peliosis hepatis, cholestasis, hepatic adenoma/carcinoma) characteristic of 17α-alkylated oral AAS. It is comparatively favorable on liver risk — but not entirely risk-free, and oral exposure still passes through the liver.
Cardiovascular / lipids: As with AAS generally, supraphysiologic androgen use lowers HDL and raises LDL, promoting an atherogenic profile. The broader AAS literature links abuse to hypertension, left-ventricular hypertrophy/dysfunction, accelerated atherosclerosis, arterial stiffness, prothrombotic changes, and increased risk of myocardial infarction and sudden cardiac death. Non-aromatizing DHT-derived androgens like methenolone tend to be particularly suppressive of HDL.
HPTA suppression / infertility: All exogenous androgens suppress the hypothalamic-pituitary-testicular axis, reducing LH/FSH and endogenous testosterone, with consequent impaired spermatogenesis, testicular atrophy, and potential infertility (often reversible, but not always).
Gynecomastia / estrogenic effects: Because methenolone does not aromatize, direct estrogenic gynecomastia is unlikely from methenolone itself.
Virilization (in women): Despite being “mild,” it is androgenic and can cause hirsutism, voice deepening, menstrual disruption, and clitoral enlargement; some virilizing effects are irreversible.
Hematologic: Androgens stimulate erythropoiesis and can raise hematocrit/red cell mass (the basis of its anemia use), which at supraphysiologic doses can raise thrombotic/viscosity concerns.
Other AAS-class risks: mood and behavioral changes, acne, androgenic alopecia, and the hazards of contaminated or underdosed illicit product — the dominant supply today.

Honest framing: the “mild and safe” reputation is relative, reflecting mainly low hepatotoxicity and no aromatization — not an absence of cardiovascular, endocrine, or virilizing harm.

Bottom line

Methenolone is a DHT-derived anabolic steroid with a real but narrow and dated medical record — small, mixed studies in bone-marrow-failure anemias and a historical role in advanced breast cancer. Its modern popularity rests on a “mild and safe” physique reputation that controlled human trials have never validated. It is genuinely lower-risk for liver injury than 17α-alkylated orals and does not cause estrogenic gynecomastia, but it remains HPTA-suppressive, virilizing, and HDL-lowering, and it is a Schedule III controlled substance in the US and banned at all times in sport. The honest read: for performance and physique claims, the evidence is preliminary at best and the legal and health downsides are concrete.

Evidence grade: Preliminary human.

Methenolone (Primobolan)