Trenbolone
Also known as: tren
A very potent androgen developed for livestock, never licensed for humans, with a side-effect reputation as strong as its anabolic one.
Legal status: UK: Class C controlled drug and prescription-only medicine. Supplying it (including to friends) and importing it by post are criminal offences; personal possession for your own use generally is not. Checked 2026-07-26.
Prohibited in sport: Yes — on the WADA Prohibited List.
What it is
Trenbolone is a synthetic androgen developed for veterinary use: it is given to cattle to increase growth rate and feed efficiency. It has never been a licensed human medicine anywhere. It binds the androgen receptor far more strongly than testosterone and does not aromatise to oestrogen.
What’s claimed
- Dramatic strength and muscle gain with simultaneous fat loss
- Hardness and vascularity without water retention
- The strongest compound available short of growth hormone
What the evidence shows
Almost none of this rests on human evidence. Trenbolone's anabolic effects are documented in cattle, where the outcome measured is carcass weight; there are effectively no controlled human trials, because no ethics committee would approve one. The strength of the anecdotal reputation is not a substitute (Bronze at best, and on animal data). What is well documented in humans is the harm profile, through case reports and clinical experience, and it is among the worst of any compound in this library.
The risks
- Cardiovascular: severe and rapid suppression of HDL cholesterol, raised blood pressure, and a strong association with cardiomyopathy in case reports.
- Psychiatric: pronounced aggression, anxiety, insomnia and paranoia are so commonly reported that they are treated as characteristic of the compound.
- Autonomic: night sweats, sharply reduced cardiovascular endurance and a persistent cough on administration.
- Endocrine: suppression of the body's own testosterone production, with testicular atrophy and impaired fertility. Recovery is not guaranteed and can be slow or incomplete.
- Progestogenic: gynaecomastia driven by progestogenic rather than oestrogenic activity, which does not respond to the usual approaches.
- Renal: case reports of kidney injury, some severe.
What needs monitoring
- Full blood count, including haematocrit and haemoglobin
- Lipid profile
- Blood pressure
- Liver and kidney markers
- Testosterone and the wider hormonal axis: a doctor is the right person to arrange these tests and to interpret what they show.
Sources
- NHS. Anabolic steroid misuse — health risks and the law.
- GOV.UK. Controlled drugs: Misuse of Drugs Act 1971 drug classes.
- World Anti-Doping Agency. The Prohibited List.
- Pope HG, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341-375.