Metribolone
Also known as: Methyltrienolone, Metribolone, M3, R1881, Oral Tren, Methyltrienolone (R1881)
Lower numbers = closer to natural. Higher numbers = more enhanced.
Why this rating?
Metribolone is one of the most potent anabolic-androgenic steroids ever synthesised, a 17-alpha-methylated relative of trenbolone with roughly 200% of testosterone's androgen-receptor affinity, active in microgram-to-low-milligram doses. Any physique effect is inseparable from extreme toxicity, and it is used (if at all) only in tiny pre-contest doses. The combination of extreme potency and severe organ toxicity places it at the very top of the enhancement scale.
Overview
An extraordinarily potent oral steroid (a 17-alpha-methylated trenbolone analogue) that was abandoned in development for being too toxic to use. Today it exists mainly as the androgen-receptor research ligand R1881, and, recklessly, as a microgram-dosed pre-contest compound. It is widely regarded as one of the most hepatotoxic androgens ever made.
Important Warnings
- •One of the most hepatotoxic androgens ever produced. Severe liver dysfunction has occurred at doses under 1mg/day
- •Never approved for human use; abandoned in development for toxicity
- •Not a safe "oral trenbolone": the 17-alpha-methyl group makes it far more toxic than injectable tren
- •Do NOT combine with other hepatotoxic orals (Anadrol, Halotestin). The liver strain is multiplicative
- •Not appropriate for beginners under any circumstances; avoidance is the honest recommendation
Purpose & Use Cases
Research Reference Androgen (R1881)
Its dominant legitimate use: a high-affinity radioligand and reference agonist for studying the androgen receptor in the laboratory.
Pre-Contest Hardness / Aggression (reckless use)
A tiny minority of bodybuilders use microgram-to-low-milligram doses in the final pre-contest days for hardness and drive, a practice defined by its danger, not its wisdom.
Benefits
- Extreme potency at microgram-to-milligram doses
- Non-aromatizing: no estrogenic water retention
- Dramatic strength, hardness and aggression
- Invaluable as the R1881 androgen-receptor research ligand
Good to Know
One of the most toxic steroids ever made
Metribolone was investigated for advanced breast cancer in the late 1960s-early 1970s and abandoned because it caused severe liver dysfunction at very low doses. It has been described as roughly equivalent to taking high-dose Anadrol and high-dose Halotestin at the same time. There is no dose at which it is reasonably safe.
It is "R1881," a lab reference androgen
Its most legitimate role is scientific: as the radiolabelled ligand R1881, it is a standard high-affinity tool for measuring androgen-receptor binding. In other words, the compound is best known to researchers as an assay reagent, not to athletes as a usable drug.
Not simply "oral trenbolone"
It is often marketed as "oral tren," and it is structurally methylated trenbolone, but the 17-alpha-methyl group that makes it oral also makes it dramatically more hepatotoxic than injectable trenbolone. Treating it as a convenient oral version of tren badly understates the danger.
Progestogenic like the other 19-nors
With ~208% progesterone-receptor affinity, metribolone carries the same prolactin/progestin risks as trenbolone and nandrolone (low libido, mood and erectile issues) so a testosterone base and prolactin monitoring apply, on top of the liver and lipid concerns.
Why it is rated 10
The natty scale tops out at extreme, unambiguous enhancement. Metribolone is active in microgram doses, wildly potent at the androgen receptor, and so toxic it was deemed unfit for medicine, the pharmacological opposite of anything achievable naturally, and among the most dangerous compounds a person can take.
Dosage Guidelines
| Experience Level | Dosage Range |
|---|---|
| Beginner | 0 – 0 mg/day |
| Intermediate | 0.5 – 1 mg/day |
| Advanced | 1 – 2 mg/day |
There is no "safe" beginner dose. This compound is not appropriate for beginners under any circumstances. Even sub-milligram daily doses have caused severe liver dysfunction in clinical trials. These ranges reflect community-reported "oral tren" protocols, not any clinical guideline. Metribolone was never approved for human use, so no official dosing standard exists. Any use is high-risk and very short.
Not well characterised in humans (an oral 17-alpha-alkylated steroid); the effect is thought to last only hours per dose.
Side Effects
Extreme Hepatotoxicity
very commonOne of the most liver-toxic androgens ever produced. Human breast-cancer trials were halted because severe hepatic dysfunction appeared at very low doses, even ~1mg/day can damage the liver.
There is no reliable mitigation. TUDCA and extremely short, tiny-dose use reduce but do not remove the risk. The honest advice is to avoid it.
Catastrophic Lipid Damage
very commonSeverely suppresses HDL and worsens the whole cholesterol profile, sharply raising cardiovascular risk.
Omega-3, citrus bergamot and cardio are inadequate against a compound this harsh; short duration is the only real limiter.
Elevated Prolactin / Progestogenic Sides
commonStrong progesterone-receptor activity (like trenbolone/nandrolone) can raise prolactin and cause libido, mood and erectile issues.
Cabergoline if prolactin is elevated; a testosterone base for androgenic support.
Total HPTA Suppression
very commonProfoundly shuts down natural testosterone production even at tiny doses.
Testosterone base and full PCT: though the toxicity is the dominant concern, not recovery.
Severe Aggression & CNS Effects
commonExtreme androgenic drive can produce dangerous aggression and mood disturbance, similar to trenbolone/Halotestin.
Only relevant in tightly controlled settings; another reason recreational use is inadvisable.
General Mitigation Strategies
Realistically, the only meaningful mitigation is not to use it. It is not orally alkylated "like most orals". It is in a class of its own for toxicity, and severe liver dysfunction has occurred at sub-milligram doses. If used at all, doses are microgram-to-low-milligram, duration is a few days, TUDCA and a full lipid/liver panel are baseline, and a testosterone base plus prolactin control address its progestogenic side. None of this makes it safe.
Support Supplements
Ancillary supplements commonly run alongside Metribolone to manage side effects, support the target tissue, or fill nutrient demands it creates.
Liver support (TUDCA + NAC)
KeySupports bile flow and hepatic glutathione against 17-alpha-alkylated liver strain, necessary but nowhere near sufficient for a compound this toxic.
- Dose
- TUDCA 500-1,000mg/day; NAC 600-1,200mg/day
- Timing
- Throughout any use
- When
- Does NOT make metribolone safe. Severe hepatotoxicity has occurred at doses under 1mg/day regardless of support. Dose/duration limits and bloodwork are the real protection, and avoidance is safer still.
Lipid support (omega-3 + citrus bergamot)
Blunts some of the catastrophic HDL suppression, but is outmatched by this compound.
- Dose
- Omega-3 2-4 g/day; citrus bergamot 500-1,000mg/day
- Timing
- With meals
- When
- Support only: cannot offset the lipid damage at meaningful doses.
Cabergoline (dopamine agonist)
Controls prolactin elevation from metribolone's strong progestogenic activity.
- Dose
- 0.25mg 2x/week, titrated to prolactin labs
- Timing
- With food
- When
- Only if bloodwork shows elevated prolactin.
Post Cycle Therapy (PCT)
Metribolone causes total HPTA shutdown, so PCT is required, but the dominant issue is toxicity rather than recovery. Standard SERM PCT (e.g. Nolvadex 40/40/20/20mg/day) after the short course, with bloodwork for liver enzymes, lipids, prolactin and the hormonal axis. hCG can be used pre-PCT for testicular recovery.
How It Works
Metribolone (R1881) is a synthetic 17-alpha-alkylated 19-nor (estrane) steroid, essentially methylated trenbolone. It binds the androgen receptor with extremely high affinity (~204% of testosterone) and also strongly activates the progesterone receptor (~208%). It does not aromatize. Its 17-alpha-methyl group makes it orally active but also drives severe liver toxicity. So potent it is used as a radiolabelled "hot ligand" (R1881) in androgen-receptor binding assays.
Hormonal & Androgenic Profile
Extraordinarily potent: androgen-receptor affinity ~204% of testosterone (and ~208% progesterone-receptor affinity); animal work reported roughly 120-300x the oral anabolic and 60-70x the androgenic potency of methyltestosterone.
Does not aromatize, no AI needed. Its estrogen-independent sides (lipids, prolactin, liver) are the concern, not estradiol.
A 19-nor (estrane) steroid, not a DHT derivative and not a 5-alpha-reductase substrate in a way that matters here, so finasteride/dutasteride are irrelevant to its side-effect profile.
Severe HDL suppression and lipid damage on top of extreme hepatotoxicity, one of the harshest cardiovascular/organ profiles of any AAS.
Fundamentals
Reference on the practices relevant to Metribolone: how they are done and where they go wrong. Not a recommendation to use it.
Common Stacks
- Metribolone is not a compound to build a stack around. Its use is niche, tiny-dose and high-risk, always over a testosterone base if used at all
Legal Status
Never approved for human medical use; a controlled anabolic steroid (Schedule III-class in the USA) sold only as a research chemical or grey-market "oral tren".
Legal status varies by country and changes over time. This is a general summary, not legal advice.
WADA Status
Methyltrienolone (metribolone) is explicitly prohibited at all times as an exogenous anabolic androgenic steroid.