Trenbolone

Trenbolone is a synthetic anabolic steroid approved only as an ear implant to increase weight gain in beef cattle. It has never been approved as a medicine for people.

What it is

Trenbolone is a synthetic anabolic–androgenic steroid. It is a veterinary product. In the US it is approved as trenbolone acetate in ear implants for beef cattle, often combined with oestradiol, to increase growth rate and feed efficiency ^{[1, 2]}. It has never been approved as a medicine for people, and the US Drug Enforcement Administration describes it as used only in veterinary medicine ^[3]. The cattle product labels state that it is not for use in humans ^[2]. It is a Schedule III controlled substance in the US and a Class C drug in the UK ^{[12, 13]}.

How it works

Trenbolone acts on the androgen receptor, the same receptor that testosterone uses. Laboratory studies show it binds this receptor more strongly than testosterone does ^[4]. Unlike testosterone, it is not converted into oestrogen, but it does bind strongly to the progesterone receptor ^[4]. In cattle, trenbolone acetate is quickly converted to the active form, trenbolone, which is then broken down into other forms found in liver, bile and urine ^[5].

Approved medical uses

None in people.

In the US, trenbolone acetate is approved only as an implant for cattle raised for slaughter, to increase rate of weight gain and feed efficiency ^{[1, 2]}. The FDA requires that hormone residues left in edible tissue are below a set safe level ^[1]. In the EU, giving substances with androgenic action to farm animals for growth is prohibited ^[6].

What the research shows

• Human evidence is very limited. There are no modern clinical trials in people. Most human information comes from surveys of people using several steroids at once and from case reports of harm ^{[4, 7]}.
• Old volunteer data. A WHO expert committee review of the veterinary drug noted only limited human volunteer data, with effects on protein balance and menstrual disturbances in women ^[5].
• Animal and laboratory studies. A 2024 review found that most research on trenbolone's effects on the brain, testes and immune system comes from rats, fish, cattle and cell cultures. The authors state that effects on human nerve tissue have not been confirmed ^[4].
• Case reports of harm. A published case described severe heart failure (cardiomyopathy) in a man using trenbolone with other steroids. The authors judged that recent trenbolone use may have contributed. Heart function improved after he stopped all steroids and received standard heart failure treatment ^[8].
• Difficult to study alone. Because people who use trenbolone usually combine it with other steroids, it is hard to link specific harms to trenbolone itself ^{[4, 7]}.

Known risks and side effects

Most known risks come from case reports, animal studies and the wider evidence on non-medical anabolic steroid use, often at supraphysiological doses.

• Heart and blood vessels: non-medical use of anabolic steroids is linked to cardiovascular disease and an increased risk of death ^[7]. Trenbolone has been implicated in a case of severe cardiomyopathy ^[8]. Heart attack, stroke, high blood pressure and blood clots are reported with steroid misuse ^[9].
• Hormones and fertility: suppression of the body's own testosterone and of the pituitary hormones LH and FSH, testicular shrinkage, and low or absent sperm counts ^{[4, 9]}.
• Breast tissue: breast enlargement in men has been reported, possibly linked to its action on the progesterone receptor ^[4].
• Mental health: aggression, mood swings, anxiety and paranoia; steroids can cause dependence, with depression and other withdrawal symptoms on stopping ^{[4, 9]}.
• Effects in women: facial and body hair growth, deepened voice and other changes that may not reverse ^[9].
• Injection-related harms: inflammation and tissue damage at injection sites, and infections such as hepatitis B, hepatitis C and HIV from shared needles ^{[4, 9]}.
• Sport: trenbolone is prohibited at all times under the World Anti-Doping Agency (WADA) Prohibited List ^[10].

Blood tests commonly monitored

There are no official monitoring guidelines for trenbolone, because it is not approved for use in people. For testosterone, the closest approved medicine in this class, the Endocrine Society guideline recommends monitoring ^[11]:

• Testosterone level during treatment ^[11].
• Haematocrit (the proportion of red blood cells), with treatment withheld if it rises above 54% ^[11].
• PSA (prostate-specific antigen) in men, with urology referral for a confirmed rise ^[11].

Anyone who has used trenbolone should talk to a doctor about appropriate tests.

Sources

1. US Food and Drug Administration. Steroid Hormone Implants Used for Growth in Food-Producing Animals. FDA, 2024. FDA
2. Zoetis Inc. SYNOVEX Choice (trenbolone and estradiol implant) product label. US FDA, accessed 2026. FDA label
3. US Drug Enforcement Administration, Diversion Control Division. Anabolic Steroids (drug and chemical information). DEA, 2025. DEA
4. Borecki R, Byczkiewicz P, Słowikowska-Hilczer J. Impact of trenbolone on selected organs. Endokrynologia Polska, 2024. Endokrynologia Polska
5. Joint FAO/WHO Expert Committee on Food Additives. Trenbolone acetate. WHO Food Additives Series 23, 1988. INCHEM
6. Council of the European Union. Council Directive 96/22/EC concerning the prohibition on the use in stockfarming of certain substances having a hormonal or thyrostatic action and of beta-agonists. EUR-Lex, 1996 (consolidated 2008). EUR-Lex
7. Pope HG Jr, Wood RI, Rogol A, Nyberg F, Bowers L, Bhasin S. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocrine Reviews, 2014. Endocrine Society
8. Han HC, Farouque O, Hare DL. Steroid-induced cardiomyopathy. Medical Journal of Australia, 2015. MJA
9. NHS. Anabolic steroid misuse. NHS website, 2026. NHS
10. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. WADA, 2025. WADA
11. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism, 2018. Endocrine Society
12. Home Office. List of most commonly encountered drugs currently controlled under the misuse of drugs legislation. GOV.UK, 2025. GOV.UK
13. US Code of Federal Regulations. 21 CFR 1308.13, Schedule III. Legal Information Institute, Cornell Law School, accessed 2026. LII

Related

Last reviewed 7 October 2026. General information, not medical advice. Found a mistake? Email [email protected].