Methyltrienolone (Metribolone, R1881)

What methyltrienolone is and how it works

Methyltrienolone has the chemical name 17β-hydroxy-17α-methylestra-4,9,11-trien-3-one. It corresponds to trenbolone with a methyl group in the 17α position, which makes it effective as a tablet but puts more strain on the liver. A review describes it as a 17α-methylated trenbolone that was widely used in research as a ligand and photoaffinity label for the androgen receptor (Tauchen 2021).

Its importance for research is explained by two properties. First, it binds to the androgen receptor more tightly than the body’s own androstanolone, DHT, as measured in rat prostate tissue. Second, unlike the body’s own androgens, it is not bound by transport proteins in the blood. This made it possible to measure androgen receptors in human tumors as well, without traces of blood distorting the result (Bonne and Raynaud 1975). In human prostate tissue it was shown to also dock onto a binding site with properties of the progesterone receptor (Menon 1978). In cell experiments it also binds to the mineralocorticoid receptor as tightly as aldosterone, but does not activate it; instead it blocks it (Takeda 2007). An overview of the substance group can be found under Anabolic steroids (anabolics, AAS).

What the studies show

The early clinical papers

In 1965 a paper appeared in France with the title “Protein building in humans by a new steroid: methyltrienolone” (Trémolières 1965). In 1966 a paper on the liver toxicity of the new anabolic followed (Krüskemper and Noell 1966), and in 1970 a study on efficacy and toxicity in advanced breast cancer (Halden 1970). No abstract is available for any of these papers; patient numbers and results therefore cannot be reported here.

Why it never came onto the market

A review on the medical use of testosterone and related steroids summarizes: methyltrienolone was considered as a treatment for advanced breast cancer in women, but was never marketed for medicine because it is strongly liver-toxic even at very low doses (Tauchen 2021).

Receptor studies in human tissue

Menon 1978 used methyltrienolone to examine tissue from 30 enlarged prostates and other male tissues. In 29 of 30 samples, high-affinity binding was found. In the cell nucleus it behaved like an androgen receptor, whereas in the cytoplasm of the prostate it behaved more like a progesterone receptor. This was important for research, because measurements with methyltrienolone have to be interpreted differently depending on the tissue.

A case report from the present

Fisler 2018 describes a 56-year-old man who injected steroids bought on the internet. According to the label, they contained testosterone propionate, testosterone acetate, drostanolone propionate and methyltrienolone. He developed severe jaundice and kidney damage in which bile pigments blocked the renal tubules; 4 weeks of dialysis were necessary, after which the liver and kidneys recovered. The doctors did not have the contents of the ampoules analyzed; what part methyltrienolone played remains open.

Where the data stop

There is no controlled study of methyltrienolone in humans, neither on efficacy nor on safety. The early papers are small, old and accessible only in the original. How strongly the substance builds muscle in humans, how quickly it is broken down and in what amount it damages the liver has not been quantified.

The case report also helps only to a limited extent: the man took several steroids, and whether the label was correct was not checked. Laboratory research with methyltrienolone is extensive, but says little about the effect of taking it.

Status, approval and legal

Methyltrienolone is not approved as a medicine in Germany, the EU or the US and was never marketed for medicine (Tauchen 2021). In research it has been used since the 1970s as a ligand for androgen receptors.

In Germany it is listed by name as metribolone, synonym methyltrienolone, in the annex of the Anti-Doping Act: manufacturing, trading and placing it on the market for doping are prohibited, as are acquisition, possession and bringing it into the country in more than a small quantity for doping in sport (§ 2, punishable under § 4). On the WADA Prohibited List 2026 it is listed under S1.1 as metribolone and is prohibited at all times.

Safety

The central risk is the liver. As early as 1966 a paper dealt with the liver toxicity of the substance (Krüskemper and Noell 1966), and a recent review calls it strongly liver-toxic even at very low doses (Tauchen 2021). For the group of 17α-methylated steroids, cholestasis, peliosis hepatis and liver tumors have been described, see Methasterone (Superdrol) and Oxymetholone (Anadrol).

In addition, there is the effect on the mineralocorticoid receptor shown in cell experiments (Takeda 2007); what it means for salt and water balance in humans has not been studied. The general risks of anabolic steroids for the hormone axis, heart and psyche also apply here, see Anabolic steroids (anabolics, AAS). There are no substance-specific data on this.

Sources

• Bonne C, Raynaud JP, Steroids 1975 – methyltrienolone as a specific ligand for androgen receptors
• Menon M et al., J Clin Invest 1978 – binding of methyltrienolone to human tissues
• Takeda AN et al., Mol Pharmacol 2007 – methyltrienolone (R1881) as an antagonist at the mineralocorticoid receptor
• Trémolières J, Péquignot E, Presse Med 1965 – protein building in humans by the new steroid methyltrienolone (French)
• Krüskemper HL, Noell G, Steroids 1966 – liver toxicity of the new anabolic methyltrienolone
• Halden A et al., Cancer Chemother Rep 1970 – efficacy and toxicity of methyltrienolone in advanced breast cancer
• Tauchen J et al., Molecules 2021 – medical use of testosterone and related steroids, review including designer steroids
• Fisler A et al., Case Rep Nephrol Dial 2018 – kidney damage from bile casts after steroids bought on the internet, case report
• German Anti-Doping Act (AntiDopG), § 2, § 4 and annex
• NADA – Prohibited List 2026, informational German translation (S1.1 anabolic-androgenic steroids)