Methyltrienolone, also called metribolone or by its laboratory code R1881, is a synthetic anabolic-androgenic steroid (AAS). Chemically it is trenbolone with a methyl group added at carbon 17α, the change that lets steroids such as methyltestosterone survive a first pass through the liver when taken by mouth (Tauchen et al., Molecules 2021).
It was tested in people in the 1960s, including as a possible treatment for advanced breast cancer. It was never marketed as a medicine, and a 2021 review attributes this to strong liver toxicity even at very low doses (Tauchen et al., Molecules 2021; Krüskemper and Noell, Steroids 1966). Since the 1970s its main use has been as a radiolabeled research tool for measuring androgen receptors in tissue samples. No modern controlled human trials exist.
This page summarizes what the early clinical reports, laboratory studies and regulators report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Synthetic 17α-methylated anabolic-androgenic steroid; 17α-methyl derivative of trenbolone |
| Other names | Metribolone, R1881, RU 1881, NSC-92858 |
| Formula and weight | C₁₉H₂₄O₂, 284.4 g/mol |
| Medical approval | None; never marketed as a medicine |
| Human data | A few clinical reports from 1965–1970, including a liver toxicity report; no controlled trials |
| Route studied | Oral |
| Half-life | No published human pharmacokinetic data found |
| Key mechanism fact | Binds the androgen receptor more tightly than DHT and is not bound by SHBG; also binds progesterone and mineralocorticoid receptors |
| US status | Schedule III anabolic steroid (named in 21 CFR 1308.13) |
| WADA status | Prohibited at all times (S1.1 anabolic androgenic steroids) |
What it is
Methyltrienolone’s chemical name is 17β-hydroxy-17α-methylestra-4,9,11-trien-3-one (PubChem CID 261000). Like nandrolone and trenbolone, it is a “19-nor” (estrane) steroid: it lacks the carbon-19 methyl group of testosterone. It shares trenbolone’s three double bonds at positions 4, 9 and 11. The one difference from trenbolone is the extra 17α-methyl group.
| Compound | Chemical name | Formula | Notes |
|---|---|---|---|
| Trenbolone | 17β-hydroxyestra-4,9,11-trien-3-one | C₁₈H₂₂O₂ | Used as acetate, enanthate or hexahydrobenzylcarbonate esters |
| Methyltrienolone | 17β-hydroxy-17α-methylestra-4,9,11-trien-3-one | C₁₉H₂₄O₂ | Not an ester; 17α-methyl group added |
For the trenbolone forms, see Trenbolone Acetate, Trenbolone Enanthate and Parabolan (Trenbolone Hexa). For another 17α-methylated steroid with a long medical record, see Methyltestosterone.
A 2021 review groups metribolone with trenbolone and tetrahydrogestrinone (THG) as steroids whose added double bonds at carbons 9–10 and 11–12 increase anabolic activity (Tauchen et al., Molecules 2021). The same review notes that every anabolic steroid keeps some androgenic activity.
How it works in the body
Methyltrienolone acts mainly through the androgen receptor (AR), the same receptor testosterone and dihydrotestosterone (DHT) use. Laboratory studies show:
- Very tight AR binding. In rat prostate tissue it bound the androgen receptor more tightly than DHT (Bonne and Raynaud, Steroids 1975). In rat skeletal muscle its dissociation constant (a measure of binding; lower means tighter) was about 0.3 nM (Snochowski et al., Eur J Biochem 1980). When several anabolic steroids were compared in rat and rabbit muscle and rat prostate, methyltrienolone itself bound most strongly, ahead of nandrolone, methenolone and testosterone (Saartok et al., Endocrinology 1984).
- No SHBG binding. Unlike testosterone and DHT, it is not bound by human sex hormone-binding globulin (SHBG), the blood protein that carries sex steroids (Bonne and Raynaud, Steroids 1975; Menon et al., J Clin Invest 1978).
- Progesterone receptor binding. It also binds the progesterone receptor. In human prostate tissue, much of its binding behaved like binding to a progesterone receptor rather than to the androgen receptor (Cowan et al., J Endocrinol 1977; Menon et al., J Clin Invest 1978). Researchers had to adjust their assays to account for this (Zava et al., Endocrinology 1979).
- Mineralocorticoid receptor blocking. In cell studies it bound the mineralocorticoid receptor (the aldosterone receptor that controls salt handling in the kidney) about as strongly as aldosterone, and blocked rather than activated it (Takeda et al., Mol Pharmacol 2007).
In a cell-culture study of AR activation, methyltrienolone grouped with the “virilizing” androgens testosterone and DHT, not with anabolic steroids such as oxandrolone, stanozolol and nandrolone (Holterhus et al., J Steroid Biochem Mol Biol 2002). All of these findings come from tissue extracts and cultured cells. They describe how the molecule behaves at the receptor, not what it does in a person.
Metabolism
No human pharmacokinetic study (absorption, peak levels or half-life) was found. An anti-doping laboratory incubated methyltrienolone with human liver microsomes (liver enzyme preparations) in vitro and found seven groups of phase I metabolites, formed by 17-epimerization, hydroxylation and loss of the C-18 carbon (“18-nor” metabolites). The authors suggested the 18-nor metabolites as possible long-term markers for doping tests (Yan et al., J Pharm Biomed Anal 2025).
Former clinical research
Methyltrienolone was tested in people only briefly, in the 1960s. The indexed reports include:
| Year | Report | Focus |
|---|---|---|
| 1965 | Trémolières and Péquignot, Presse Médicale (French) | Protein anabolism in humans |
| 1966 | Krüskemper and Noell, Steroids | Liver toxicity |
| 1967 | Bellastella et al. and Esposito et al., Clinica Terapeutica (Italian) | Oral use: blood proteins, nitrogen balance, calcium, phosphorus and weight |
| 1970 | Halden, Walter and Gordan, Cancer Chemotherapy Reports | Antitumor efficacy and toxicity in advanced breast cancer |
These papers have no abstracts in PubMed, and we could not access their full text. We therefore do not report their doses or results. What is clear from the record is that the drug went no further: a 2021 review states it was considered for advanced breast cancer but was never marketed because it is strongly hepatotoxic (toxic to the liver) even at very low doses (Tauchen et al., Molecules 2021).
A 1970 French report described no signs of liver toxicity in pigs fed high doses (Szumowski and Grandadam, C R Seances Soc Biol Fil 1970). This is an animal finding and does not outweigh the human liver reports.
Use as a research tool
From the mid-1970s, tritium-labeled methyltrienolone ([³H]R1881) became a standard tool for measuring androgen receptors. Because SHBG does not bind it, it can detect receptors in human tumor samples where contamination with blood plasma would otherwise interfere (Bonne and Raynaud, Steroids 1975). It was used, for example, to measure receptors in prostate tissue, seminal vesicle, epididymis and genital skin (Menon et al., J Clin Invest 1978). Mibolerone, another synthetic steroid, was later proposed for the same laboratory role (Traish et al., Endocrinology 1986); see Cheque Drops (Mibolerone).
About potency claims. Methyltrienolone is often described online as one of the most potent steroids ever made, with large anabolic:androgenic ratios. What the primary literature supports is narrower: it binds the androgen receptor very tightly in tissue extracts. Receptor binding does not by itself predict muscle gain, side effects or a safe dose in people, and no controlled human study has measured any of these.
Side effects and risks
Liver toxicity
Liver damage is the defining risk. The only human toxicity data are the 1960s reports above, which stopped its development (Krüskemper and Noell, Steroids 1966; Tauchen et al., Molecules 2021). Its 17α-methyl group is the feature that a pharmacology review associates with liver toxicity across orally active steroids, including cholestatic jaundice, peliosis hepatis (blood-filled liver cysts) and liver tumors (Kicman, Br J Pharmacol 2008).
A 2018 case report described a 56-year-old man with severe jaundice (bilirubin 680 µmol/L) and kidney failure from bile casts, who needed dialysis for 4 weeks. He had injected an internet-bought product labeled as containing testosterone propionate, testosterone acetate, drostanolone propionate and methyltrienolone. The product was not chemically tested, so the injury cannot be attributed to any one ingredient (Fisler et al., Case Rep Nephrol Dial 2018).
Effects shared with other androgens
No human studies have measured hormone suppression, lipids, blood pressure or virilization with methyltrienolone. Laboratory data show it is a strong androgen receptor activator in the same group as testosterone and DHT. It is reasonable to expect the class effects of potent androgens, but their size with this compound is unknown.
Unknown product content
Because there is no approved product, anything sold as methyltrienolone comes from outside the regulated drug supply. The Endocrine Society has noted that methyltrienolone was introduced into the market as a “dietary supplement” before the Steroid Control Act of 2004 banned most such steroids (Pope et al., Endocr Rev 2014). The identity, dose and purity of such products are not verified.
Legal status and use outside medicine
- United States. Methyltrienolone is named as a Schedule III anabolic steroid (21 CFR 1308.13). There is no FDA-approved human or veterinary product.
- Sport. Metribolone (methyltrienolone) is listed by name under S1.1 anabolic androgenic steroids, prohibited at all times, in and out of competition (WADA 2026 Prohibited List). Anti-doping labs continue to study its metabolites for detection (Yan et al., J Pharm Biomed Anal 2025).
Key takeaways
- A methylated form of trenbolone. Methyltrienolone is trenbolone with a 17α-methyl group, which makes it orally active.
- Never a medicine. It was tested in the 1960s, including for advanced breast cancer, and abandoned because of liver toxicity at very low doses.
- Mainly a laboratory reagent. Its tight androgen receptor binding and lack of SHBG binding made [³H]R1881 a standard tool for measuring androgen receptors.
- Not selective. It also binds progesterone receptors and blocks mineralocorticoid receptors in laboratory studies.
- No usable human dosing or kinetic data. No controlled trials, pharmacokinetic studies or safety data in modern populations exist.
- Controlled and banned. It is a Schedule III substance in the US and prohibited at all times by WADA.
Sources
- Tauchen J, Jurášek M, Huml L, Rimpelová S. Medicinal use of testosterone and related steroids revisited. Molecules. 2021;26(4):1032. PubMed.
- Krüskemper HL, Noell G. Liver toxicity of a new anabolic agent: methyltrienolone (17-alpha-methyl-4,9,11-estratriene-17 beta-ol-3-one). Steroids. 1966;8(1):13–24. PubMed.
- Trémolières J, Péquignot E. Protein anabolism produced in man by a new steroid: methyltrienolone [in French]. Presse Med. 1965;73(47):2655–2658. PubMed.
- Bellastella A, D’Alessandro B, Esposito V, et al. Studies of the clinical and metabolic effects of a new anabolic steroid in oral administration: methyltrienolone. I. The behavior of the blood proteins and nitrogen balance [in Italian]. Clin Ter. 1967;41(1):73–77. PubMed.
- Esposito V, Bellastella A, D’Alessandro B, et al. Study of clinical and metabolic effects of a new orally administered anabolic agent: methyltrienolone. 2. The behavior of calcium, inorganic phosphorus and weight curves [in Italian]. Clin Ter. 1967;41(2):163–167. PubMed.
- Halden A, Walter RM, Gordan GS. Antitumor efficacy and toxicity of methyltrienolone (NSC-92858) in advanced breast cancer. Cancer Chemother Rep. 1970;54(6):453–455. PubMed.
- Szumowski P, Grandadam A. Absence of hepatotoxic symptoms in swine receiving high doses of methyltrienolone in their diet [in French]. C R Seances Soc Biol Fil. 1970;164(5):984–987. PubMed.
- National Center for Biotechnology Information. PubChem Compound Summary for CID 261000, Metribolone. PubChem.
- Bonne C, Raynaud JP. Methyltrienolone, a specific ligand for cellular androgen receptors. Steroids. 1975;26(2):227–232. PubMed.
- Cowan RA, Cowan SK, Grant JK. Binding of methyltrienolone (R1881) to a progesterone receptor-like component of human prostatic cytosol. J Endocrinol. 1977;74(2):281–289. PubMed.
- Menon M, Tananis CE, Hicks LL, et al. Characterization of the binding of a potent synthetic androgen, methyltrienolone, to human tissues. J Clin Invest. 1978;61(1):150–162. PubMed.
- Zava DT, Landrum B, Horwitz KB, McGuire WL. Androgen receptor assay with [3H]methyltrienolone (R1881) in the presence of progesterone receptors. Endocrinology. 1979;104(4):1007–1012. PubMed.
- Snochowski M, Dahlberg E, Gustafsson JA. Characterization and quantification of the androgen and glucocorticoid receptors in cytosol from rat skeletal muscle. Eur J Biochem. 1980;111(2):603–616. 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.
- Traish AM, Müller RE, Wotiz HH. Binding of 7 alpha, 17 alpha-dimethyl-19-nortestosterone (mibolerone) to androgen and progesterone receptors in human and animal tissues. Endocrinology. 1986;118(4):1327–1333. PubMed.
- Holterhus PM, Piefke S, Hiort O. Anabolic steroids, testosterone-precursors and virilizing androgens induce distinct activation profiles of androgen responsive promoter constructs. J Steroid Biochem Mol Biol. 2002;82(4-5):269–275. PubMed.
- Takeda AN, Pinon GM, Bens M, et al. The synthetic androgen methyltrienolone (r1881) acts as a potent antagonist of the mineralocorticoid receptor. Mol Pharmacol. 2007;71(2):473–482. PubMed.
- Yan X, Hou J, Yan S, et al. New metabolites of methyltrienolone by in vitro human microsome and characterized using Liquid Chromatography/High Resolution Mass Spectrometry for doping control purposes. J Pharm Biomed Anal. 2025;253:116552. PubMed.
- Kicman AT. Pharmacology of anabolic steroids. Br J Pharmacol. 2008;154(3):502–521. PubMed; PMC.
- Fisler A, Breidthardt T, Schmidlin N, et al. Bile cast nephropathy: the unknown dangers of online shopping. Case Rep Nephrol Dial. 2018;8(2):98–102. PubMed.
- Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375. PubMed.
- US Drug Enforcement Administration. Schedule III, 21 CFR 1308.13(f)(62): methyltrienolone. eCFR.
- World Anti-Doping Agency. The 2026 Prohibited List, S1.1 Anabolic Androgenic Steroids. WADA 2026 Prohibited List.