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Muscle & performance

Methyltrenbolone (Metribolone)

An extremely potent 17alpha-methylated trenbolone derivative with pronounced anabolic and androgenic properties.

2 min read 14 sources

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Glass vial with golden oil and a black TPD label on a white podium, next to it a large glossy blue 3D steroid molecule in a bright lab, symbolic image for methyltrenbolone
No registered trial · not approved

Summary

At a glance

Sources checked on 26 Oct 2026

Binding to the androgen receptor
0.4 nmol/l

Ki value in the lab, the smaller the tighter the binding4

Measured with tight binding
4 receptors

Androgen, progesterone, mineralocorticoid and glucocorticoid receptor4

On the registry
0 trials

no trial with methyltrenbolone on ClinicalTrials.gov, as of 26 Oct 202613

  • Methyltrenbolone, called methyltrienolone or R1881 in research, is trenbolone with a methyl group at carbon 17. In a comparison study it bound most strongly to the androgen receptor of all steroids tested.113
  • Because it does not attach to the blood transport protein SHBG, it has served since the 1970s as a label for measuring androgen receptors in tissues.2
  • But it does not bind only there: in the lab, binding to the progesterone and mineralocorticoid receptors was almost as tight as to the androgen receptor. At the mineralocorticoid receptor it acted as a strong antagonist.46
  • In experiments it was not converted to oestrogen. A paper on liver toxicity appeared as early as 1966.810
  • The registry lists no human trial and ChEMBL lists it with phase 2 as the highest phase without approval. Everything here is the state of research, not a recommendation.1314
Profile

Updated June 2026

How long does it stay in the body?

Share left after one dose, calculated with a half-life of ~17 hours

Half-life ~17 hours
After 34 hours: 25 %
Hour 17 · 50 %Hour 34 · 25 %Hour 51 · 12.5 %Hour 85 · 3.1 %

Simplified model without an absorption phase, half-life from the TPD lexicon. The lexicon gives 16 to 18 hours, we calculate with the middle.

Class
Anabolic Steroid

methylated trenbolone

Use
Research compound

extreme potency

Half-life
Approximately 16-18 hours

daily or every-other-day

Status
WADA banned

controlled substance

Sizes
5mg/ml

1 size in the shop

Contents 13 sections
  1. At a glance
  2. What is Methyltrenbolone?
  3. How it works
  4. Application and dosing
  5. What the research shows
  6. Research status
  7. Side effects
  8. Storage
  9. PCT / after coming off
  10. Related compounds
  11. FAQ
  12. Glossary
  13. Sources

What is Methyltrenbolone?

Methyltrenbolone (Metribolone) is a synthetic anabolic steroid based on the trenbolone backbone with a 17alpha-methyl group. This structure makes it one of the most potent anabolic steroids available - at a concentration of only 5 mg/ml, it already represents significant dosing strength.

The methyl group enhances oral bioavailability, but the oil form is administered via intramuscular injection. The extreme potency at very low doses requires special care in dosing and monitoring.

This information is for research and educational purposes only. No medical advice.

Comparison

Trenbolone and relatives

Related 19-nor steroids at the androgen receptor, as described in the TPD lexicon. Tap a card to open its entry.

Trenbolone with a methyl group Methyltrenbolone (Metribolone) AR
Trenbolone, short ester Trenbolone Acetate AR Trenbolone, long ester Trenbolone Enanthate AR Nandrolone, long ester Deca (Nandrolone Decanoate) AR

In a comparison study methyltrienolone bound most strongly of all steroids tested, ahead of nandrolone, methenolone and testosterone. 3

How it works

Methyltrenbolone has an exceptionally high affinity for the androgen receptor (AR) and shows minimal aromatization to estrogen. Its potency is often described as having an androgenicity index of approximately 500-600% of testosterone baseline.

  • Extremely strong anabolic activity - rapid protein biosynthesis and nitrogen retention
  • Strong androgenic signaling without typical estrogenic side effects (no aromatization potential)
  • Intense HPG axis suppression - nearly complete inhibition of endogenous testosterone production
  • Vascular effects: Enhanced capillary dilation, initial vascularity prominence, then potentially problematic

Where it acts

Where methyltrenbolone binds in experiments

Tap a point or a card. Colour = receptor, grey = observed. All from lab and animal studies.

  1. Prostate

    Binds in rat and human prostate, in enlarged human tissue also to progestin-like sites1

    ARPR
  2. Skeletal muscle (rat)

    Binds to androgen and additionally to glucocorticoid receptors7

    ARGR
  3. Kidney (collecting duct cells)

    Blocked the effect of aldosterone on sodium transport6

    MR
  4. Hypothalamus (rat)

    Tissue made no oestrogen from it, nor did placental enzymes8

    Observed in trials
  5. Liver

    Early paper on liver toxicity from 196610

    Observed in trials

Known targets4

Compound CHEMBL166444: four described targets, type of action on each card.

Androgen receptor
Gene
AR
UniProt
P10275
ChEMBL
CHEMBL1871
Action
Very tight binding (Ki 0.4 nmol/l)
Progesterone receptor
Gene
PGR
UniProt
P06401
ChEMBL
CHEMBL208
Action
Almost equally tight binding (Ki 0.49 nmol/l)
Mineralocorticoid receptor
Gene
NR3C2
UniProt
P08235
ChEMBL
CHEMBL1994
Action
Tight binding (Ki 0.54 nmol/l), acts as an antagonist
Glucocorticoid receptor
Gene
NR3C1
UniProt
P04150
ChEMBL
CHEMBL2034
Action
Weaker binding (Ki 9.65 nmol/l)
Glossy blue 3D steroid molecules sit glowing on a transparent light blue muscle strand with fine fibres
Methyltrenbolone binds very tightly to the androgen receptor but also to other steroid receptors. Symbolic image.

Application and dosing

Dosing

Dosing, titration and syringe

Loading the dosing information …

  • Getting started and stepping up, drawn as a staircase
  • Units on the U-100 syringe for every step
  • How long one vial lasts
Glass vial with golden oil and a black TPD label, in front of it a finely graduated disposable syringe on a white table
Symbolic image.

What the research shows

Research on methyltrenbolone is limited, as it has not been studied in large clinical trials due to its potency and side effect profile. However, reports from user experience and in vitro data suggest:

  • Extreme muscle-building effects documented, often with weight gains of 10-15 lbs in 4-6 weeks in animal models
  • Cardiovascular strain was substantial in models - hypertension and LDL elevation prominent
  • Hepatotoxicity: Despite oil form, liver enzyme changes observed in some models
  • Fertility recovery difficult and may take months

Study results

What the trials measured

Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.

How tightly methyltrenbolone binds to four receptors4

Ki value in nmol/l, measured on receptors in HEK293 cell extracts, smaller means tighter

Androgen receptor4
Methyltrenbolone (lab value) 0.40 nmol/l
Progesterone receptor4
Methyltrenbolone (lab value) 0.49 nmol/l
Mineralocorticoid receptor4
Methyltrenbolone (lab value) 0.54 nmol/l
Glucocorticoid receptor4
Methyltrenbolone (lab value) 9.65 nmol/l

Methyltrenbolone was the reference compound for a new muscle drug in this paper, the values are listed in the ChEMBL activity data. A Ki value does not say whether a receptor is switched on or off.

Transparent model of a liver on a wire rack between stacked petri dishes in a bright lab cabinet
Research comes almost only from the lab and animal studies, the liver was an early topic. Symbolic image.

Research status

Where the research stands

Methyltrenbolone serves mainly as a laboratory tool. There is no human trial on the registry. As of 26 Oct 2026. 13

  1. Preclinical Binding studies on prostate tissue and cells
  2. Phase 1 no registered trial
  3. Phase 2 no registered trial
  4. Phase 3 no registered trial
  5. Approval not yet
Not approved. ChEMBL lists metribolone with phase 2 as the highest phase, without an approval year. ClinicalTrials.gov lists no trial.13

So far there is no registered trial in humans. 13

Side effects

Methyltrenbolone carries a substantial side effect profile due to its extreme potency.

  • Cardiovascular: Blood pressure spikes, LDL cholesterol elevation, HDL reduction, possible left ventricular hypertrophy
  • Androgenic: Intense acne, aggressive alopecia, facial/scalp oiliness, extreme libido increase
  • HPG axis: Complete testosterone suppression typical - longer recovery required
  • Hepatic: Potential hepatotoxicity despite oil form
  • Renal: Potential creatinine elevation, especially under dehydration
  • Psychiatric: Increased irritability, aggression, potentially severe mood swings
  • Other: Headaches, sleep disturbances, appetite suppression

Storage

Methyltrenbolone oil must be stored at room temperature, protected from light. The oil solution is stable with correct handling.

  • Temperature: 15-25°C ideal
  • Light: Store in dark (original vials or amber glass)
  • Moisture: Keep dry
  • Shelf life: 2-3 years stable with proper storage
  • Note: Small injection volumes require precise measurement - syringe-swap technique may be helpful
Four glass vials with golden oil on a white shelf, next to them a folded light blue cloth
Store the oil solution at room temperature and in the dark. Symbolic image.

Related

Related compounds

Same receptors: all in the TPD lexicon.

Methyltrenbolone (Metribolone)
Trenbolone Acetate Trenbolone without methyl group, short ester Trenbolone Enanthate Trenbolone without methyl group, long ester Tren Hex (Parabolan) Trenbolone with another ester TrenMix 200 Mix of two trenbolone esters TriTren 225 Mix of three trenbolone esters Deca (Nandrolone Decanoate) Also a 19-nor steroid

FAQ

Common questions about Methyltrenbolone (Metribolone)

Short answers, each backed by the sources below.

What is methyltrenbolone?

Chemically it is trenbolone with an additional methyl group at carbon 17, in research it is called methyltrienolone, metribolone or R1881. Doping laboratories count it among the very potent anabolic steroids of the trenbolone group. In a comparison study on muscle and prostate it bound most strongly to the androgen receptor of all steroids tested.113

What does research use R1881 for?

As a label. With radioactive R1881 androgen receptors can be counted in tissues, for example in tumours. It suits this purpose because it binds more tightly than DHT and does not attach to the blood protein SHBG. As early as the 1970s it was noticed that in human prostate tissue it also binds to progestin-like sites, measurements have to account for that.219

Does it bind only to the androgen receptor?

No. In a 2016 paper the Ki value was 0.4 at the androgen receptor, 0.49 at the progesterone receptor, 0.54 at the mineralocorticoid receptor and 9.65 nmol/l at the glucocorticoid receptor. Crystal structures show it in the androgen and the progesterone receptor. At the mineralocorticoid receptor it blocked the effect of aldosterone in kidney cells.456

Is methyltrenbolone converted to oestrogen?

Not in experiments. The very active placental enzyme made no oestrogen from methyltrienolone and neither did rat hypothalamus tissue. It also did not inhibit the conversion of testosterone.8

Has methyltrenbolone been studied in humans or approved?

It is not approved. ClinicalTrials.gov lists no trial (as of 26 October 2026) and ChEMBL lists it with phase 2 as the highest phase without an approval year. A paper on the liver toxicity of the then new anabolic steroid appeared as early as 1966. Everything here is the state of research, not a recommendation.131410

How is it detected in sport?

With liquid chromatography and mass spectrometry. In 2009 a doping laboratory in Cologne described a method for trenbolone and relatives, including methyltrenbolone, with detection limits of 0.3 to 3 ng/ml. The reason was findings in urine samples of elite athletes.11

Which side effects are known?

There are no frequencies from studies. An early paper on liver toxicity is documented. Because it also binds tightly to the progesterone and mineralocorticoid receptors, its action is not only androgenic. Reviews of anabolic steroids add suppressed own hormone production, falling HDL cholesterol and rising blood pressure.10412

Glossary

Terms explained briefly

Dotted words in the text open these explanations directly.

17-alpha methyl group
Small carbon group at carbon 17 of the steroid. It slows breakdown in the liver.
Androgen receptor
Protein inside the cell that androgens bind to. Genes are then read, for example for muscle building.
Aromatisation
Conversion of certain androgens into oestrogen by the enzyme aromatase.
Glucocorticoid receptor
Receptor for cortisol. It affects metabolism, inflammation and the breakdown of muscle protein.
Hormone axis (HPTA)
Hypothalamus, pituitary and testes together control the body's own testosterone production. Androgens from outside suppress this axis.
Ki value
Measure of binding strength in the lab. The smaller the value, the more tightly the compound sits on the receptor.
Mineralocorticoid receptor
Receptor for aldosterone. In the kidney it controls how much salt and water the body retains.
Progesterone receptor
Receptor for the hormone progesterone, found among others in the uterus, breast and prostate.
R1881 (methyltrienolone)
Research name of methyltrenbolone. Radiolabelled, it is used to measure androgen receptors.
SHBG
Sex hormone-binding globulin, a blood transport protein for testosterone and DHT.

Practice

PCT / after coming off

Anabolic substances suppress the body's own testosterone production in the research context. Anyone who comes off a cycle (rather than running it continuously) typically uses a post-cycle therapy (PCT) to restart the natural axis (HPTA).

The standard scheme in the research/literature context combines a SERM (tamoxifen and/or clomifene, alternatively enclomiphene) over roughly four weeks, optionally preceded by HCG to re-sensitise the testes before the SERM block. An aromatase inhibitor (anastrozole/exemestane) belongs more to on-cycle estrogen control than to the PCT itself.

Tip: order the PCT items together with the cycle so they are already on hand when you come off.

This information serves research and educational purposes only. Not medical advice.

Tamoxifen (Nolvadex) SERM, core of PCT View Clomid (Clomifen) SERM, core of PCT View Enclomiphene (Androxal) SERM alternative View HCG testicular restart before PCT View Arimidex (Anastrozole) aromatase inhibitor, on-cycle View Aromasin (Exemestane) aromatase inhibitor, on-cycle View

Evidence

Sources

Show all 14 sourcesHide sources 12 Studies1 Trial registry1 Database checked 26 Oct 2026

Studies

  1. Binding of R1881 in rat and human prostate

    Asselin et al., Steroids, 1976

    DOI 10.1016/0039-128x(76)90014-3 PMID 64005
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  2. Methyltrienolone as a label for androgen receptors

    Bonne und Raynaud, Steroids, 1975

    DOI 10.1016/s0039-128x(75)80023-7 PMID 171806
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  3. Binding of anabolic steroids to the androgen receptor in muscle and prostate

    Saartok et al., Endocrinology, 1984

    DOI 10.1210/endo-114-6-2100 PMID 6539197
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  4. New muscle drug with R1881 as reference, Ki values at four receptors

    Saeed et al., Journal of Medicinal Chemistry, 2016

    DOI 10.1021/acs.jmedchem.5b01168 PMID 26683992
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed, ChEMBL (Ki-Werte, CHEMBL3763123)
  5. Crystal structure of androgen and progesterone receptor with metribolone

    Matias et al., Journal of Biological Chemistry, 2000

    DOI 10.1074/jbc.M004571200 PMID 10840043
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  6. R1881 as a potent antagonist of the mineralocorticoid receptor

    Takeda et al., Molecular Pharmacology, 2007

    DOI 10.1124/mol.106.031112 PMID 17105867
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  7. Binding to glucocorticoid receptors in rat muscle

    Ho-Kim et al., Endocrinology, 1981

    DOI 10.1210/endo-109-5-1418 PMID 6975208
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  8. No conversion to oestrogen

    Doering und Leyra, Journal of Steroid Biochemistry, 1984

    DOI 10.1016/0022-4731(84)90360-1 PMID 6610078
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  9. Measuring androgen receptors with R1881 alongside progesterone receptors

    Zava et al., Endocrinology, 1979

    DOI 10.1210/endo-104-4-1007 PMID 436741
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed (Titel, ohne Abstract)
  10. Liver toxicity of the then new anabolic agent methyltrienolone

    Krüskemper und Noell, Steroids, 1966

    DOI 10.1016/0039-128x(66)90114-0 PMID 5955468
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed (Titel, ohne Abstract)
  11. Doping control of trenbolone and related compounds

    Thevis et al., Steroids, 2009

    DOI 10.1016/j.steroids.2008.10.004 PMID 19007801
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  12. Review: effects and side effects of anabolic steroids in athletes

    Hartgens und Kuipers, Sports Medicine, 2004

    DOI 10.2165/00007256-200434080-00003 PMID 15248788
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. Search on ClinicalTrials.gov

    ClinicalTrials.gov, U.S. National Library of Medicine

    Checked 26 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. Metribolone in ChEMBL

    ChEMBL, EMBL-EBI (CHEMBL166444)

    Checked 26 Oct 2026 via ChEMBL

In the shop

Methyltrenbolone (Metribolone) in the catalog

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