Trenbolone enanthate is the synthetic anabolic-androgenic steroid (AAS) trenbolone with a seven-carbon enanthate (heptanoate) ester attached. The ester makes the molecule more fat-soluble, so it is released slowly from an oil injection. It is used outside medicine, mainly in bodybuilding, as an injectable oil often called “Tren.”
The most important fact is that trenbolone enanthate has never been a licensed medicine in the US, for people or animals. FDA’s drug database lists no human trenbolone product (Drugs@FDA), and the only FDA-approved trenbolone products are trenbolone acetate ear implants for beef cattle (21 CFR 522.2476). No study has given trenbolone enanthate to people under controlled conditions. What is known comes from rat studies, older data on the active hormone, surveys of people who use trenbolone, and case reports.
This page summarizes what US regulations, toxicology reviews, animal studies and the limited human data report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Drug class | Synthetic anabolic-androgenic steroid; 19-nor (estrane) steroid related to nandrolone |
| Approval | None for humans or animals in the US; approved veterinary trenbolone products use the acetate ester |
| Route | Intramuscular oil injection (as used outside medicine and in rat studies) |
| Formula and weight | C₂₅H₃₄O₃, 382.5 g/mol; trenbolone itself is 270.4 g/mol (≈71% of the ester’s weight) |
| Studied doses | Rats only: 1.0, 3.5 and 7.0 mg per animal per week. No human dosing study exists |
| Half-life | Not measured in humans. In rats given weekly injections, blood trenbolone peaked within 48 h and stayed raised for the 7 days between doses |
| Key mechanism fact | The active hormone binds the human androgen receptor about as strongly as DHT and also binds the progesterone receptor in lab tests |
| US status | Schedule III anabolic steroid (trenbolone and its esters) |
| WADA status | Prohibited at all times (S1.1 anabolic androgenic steroids) |
What it is
Trenbolone’s chemical name is 17β-hydroxyestra-4,9,11-trien-3-one. Like nandrolone, it lacks the carbon-19 methyl group of testosterone, which makes it a “19-nor” steroid. It also has three double bonds in its ring system, at positions 4, 9 and 11 (PubChem CID 25015). Trenbolone enanthate attaches a heptanoic acid ester at the 17β position (PubChem CID 20112041).
The ester has no hormonal activity of its own. Once it is cleaved off, the body sees the same hormone, 17β-trenbolone, whichever ester was injected. The ester changes only how fast the drug leaves the injection site. Longer, more fat-soluble esters are released more slowly. The table compares the three trenbolone esters in this library, using PubChem’s computed fat-solubility score (XLogP3; higher means more fat-soluble):
| Form | Formula | Molecular weight | Trenbolone by weight | XLogP3 |
|---|---|---|---|---|
| Trenbolone (free hormone) | C₁₈H₂₂O₂ | 270.4 g/mol | 100% | 1.9 |
| Trenbolone acetate | C₂₀H₂₄O₃ | 312.4 g/mol | ≈87% | 2.5 |
| Trenbolone enanthate | C₂₅H₃₄O₃ | 382.5 g/mol | ≈71% | 4.9 |
| Trenbolone hexahydrobenzylcarbonate | C₂₆H₃₄O₄ | 410.5 g/mol | ≈66% | 5.2 |
Sources: PubChem CID 25015, CID 66359, CID 20112041, CID 20055297. The “by weight” column is the ratio of molecular weights. It means that 100 mg of trenbolone enanthate contains about 71 mg of trenbolone.
How it acts on receptors
Laboratory binding studies of 17β-trenbolone found (Bauer et al., APMIS 2000):
- Androgen receptor: affinity for the recombinant human androgen receptor similar to that of dihydrotestosterone (DHT). A later review describes it as about three times the affinity of testosterone (Yarrow et al., Steroids 2010).
- Progesterone receptor: slightly higher affinity than progesterone itself for the bovine (cow) progestin receptor. This was a cow receptor tested in vitro, so what it means in people is unknown.
- Metabolites: the two main metabolites, 17α-trenbolone and trendione, had under 5% of the parent hormone’s androgen receptor affinity.
- SHBG: binding to sex hormone-binding globulin was much lower than DHT’s.
Testosterone is converted in some tissues to the stronger androgen DHT by the enzyme 5α-reductase, and to estradiol by aromatase. Trenbolone is instead metabolized to weaker androgens. Researchers have proposed this as the reason it caused less prostate growth than testosterone in rats (Yarrow et al., Steroids 2010).
Pharmacokinetics
No pharmacokinetic study of trenbolone enanthate has been published in humans. The best direct data come from a rat pilot study (Yarrow et al., AJP-Endo 2011). Data on the free hormone come from cattle, in-vitro work and two small human metabolism studies.
| Setting | Finding |
|---|---|
| Rats, 7.0 mg trenbolone enanthate IM on day 0 and day 7 (n = 5) | Blood trenbolone stayed raised throughout the 7 days after each injection; peak 46.0 ng/mL on day 9, within 48 h of the second dose |
| Cows, IV trenbolone acetate | Once the ester was removed, free trenbolone left the blood with a half-life of 1.5 h |
| Human plasma, in vitro | Trenbolone bound mainly to albumin; about 4% was free |
| Total blood clearance | 17β-trenbolone cleared about twice as fast as testosterone |
| One human, oral radiolabeled 17β-trenbolone, 0.04 mg/kg | 54% of the dose in urine by 26 h and 63% by 72 h |
Cattle, in-vitro and clearance data are from the Joint FAO/WHO Expert Committee on Food Additives (JECFA) review (WHO Food Additives Series 23, 1988). The human urine study found mainly glucuronide conjugates of 17α-trenbolone, 17β-trenbolone and trendione, and noted that human metabolism differed significantly from rat metabolism (Spranger & Metzler, J Chromatogr 1991).
A doping-control study gave healthy male volunteers 10 mg of trenbolone by mouth, on the skin or inside the cheek, and collected urine for one week. Major metabolites were detected in all participants, but how long they stayed detectable varied strongly by route (Krombholz et al., Steroids 2026).
The practical point: free trenbolone itself is cleared quickly. The enanthate ester is what stretches out its presence, by slowing release from the oil depot. How long that takes in human muscle has not been measured. Half-life figures quoted for trenbolone enanthate online are not backed by a published human study.
Regulatory status
No approved product
FDA regulations approve trenbolone only as trenbolone acetate, alone or combined with estradiol or estradiol benzoate, in implants placed under the skin of the ear in beef cattle (21 CFR 522.2476; 522.2477; 522.2478). No US regulation approves the enanthate ester, and FDA’s database lists no human trenbolone product (Drugs@FDA).
Controlled substance status
Trenbolone is listed by name as a Schedule III anabolic steroid, and the listing covers its “salts, esters and ethers,” which includes the enanthate (21 CFR 1308.13). The DEA definition of “anabolic steroid” exempts steroids approved for implantation in cattle, but not when anyone prescribes, dispenses or distributes them for human use (21 CFR 1300.01). Trenbolone enanthate is not an approved cattle implant, so this exemption does not apply to it.
Sport
Trenbolone is named in section S1.1 (anabolic androgenic steroids) of the World Anti-Doping Agency 2026 Prohibited List, which covers listed substances “including their esters.” All S1 substances are prohibited at all times, in and out of competition (WADA; official text in Tractatenblad 2026, 25). Anti-doping labs have developed tests that detect the intact trenbolone enanthate ester in dried blood spots, which proves the ester was injected (Tretzel et al., J Pharm Biomed Anal 2014).
What the research shows
No human trials
No controlled study has given trenbolone enanthate to people. The only human dosing study of any trenbolone ester used the acetate. In 1967, male and female volunteers received 5 or 10 mg of trenbolone acetate intramuscularly every other day for 14 days (Krüskemper et al., Arzneimittelforschung 1967). As summarized by JECFA (WHO Food Additives Series 23):
- the 5 mg dose produced nitrogen retention, an early marker of an anabolic (protein-building) effect;
- at 10 mg, some women had menstrual cycle disturbances;
- the 10 mg dose caused a slight but significant fall in urinary 17-ketosteroids (breakdown products of the body’s own androgens);
- blood protein, cholesterol and clotting tests were unaffected over the 2 weeks.
No study has measured muscle, strength or body composition in people given trenbolone in any form.
Rat studies with the enanthate ester
The enanthate is the ester used in a series of rat studies from the University of Florida and the Gainesville VA. These are results in rats, and rat doses cannot be translated to people.
In the first study, 3-month-old male rats were castrated (orchiectomy) and given weekly trenbolone enanthate at three doses, a high dose of testosterone enanthate, or vehicle (sesame oil) for 29 days, with 10 rats per group (Yarrow et al., AJP-Endo 2011):
| Group (weekly dose, per rat) | Levator ani/bulbocavernosus muscle vs intact controls | Prostate mass vs intact controls | Hemoglobin vs intact controls |
|---|---|---|---|
| Trenbolone enanthate 1.0 mg | +35–40% | No increase | No difference |
| Trenbolone enanthate 3.5 mg | +35–40% | No increase | ≈ +8–10% |
| Trenbolone enanthate 7.0 mg | +35–40% | +68% | ≈ +8–10% |
| Testosterone enanthate 7.0 mg | +35–40% | +84% | No difference |
The levator ani/bulbocavernosus is a small, unusually androgen-sensitive muscle in rodents. Three ordinary limb muscles weighed (soleus, plantaris and semimembranosus) were not changed by any treatment. All trenbolone doses partly prevented the bone density loss and visceral fat gain caused by castration, in a dose-dependent way.
Two follow-up studies in 10-month-old castrated rats compared 1.0 mg/week trenbolone enanthate with 7.0 mg/week testosterone enanthate:
- over 5 weeks, both fully prevented the castration-induced loss of trabecular bone density; trenbolone also raised femoral neck strength by 28%, and its prostate mass was 64% below the testosterone group’s (McCoy et al., Bone 2012);
- over 29 days, both roughly doubled muscle fiber cross-sectional area in the levator ani/bulbocavernosus compared with untreated castrated rats (+94% with trenbolone, +102% with testosterone) and raised satellite cell (muscle stem cell) numbers (Dalbo et al., Andrologia 2017).
The authors proposed trenbolone as a candidate for androgen replacement that spares muscle and bone with less prostate growth. That idea has not been tested in humans.
Surveys of people who use trenbolone
Surveys do not separate the enanthate from other trenbolone esters. The largest used the Global Drug Survey 2024 and compared 237 men who had injected trenbolone in the past year with 909 men who used other AAS but not trenbolone (Bonenti et al., Drug Alcohol Rev 2026). Selected self-reported concerns:
| Concern | Other AAS, no trenbolone | Trenbolone |
|---|---|---|
| Negative impact on heart | 31.2% | 54.4% |
| Negative impact on liver | 22.4% | 42.2% |
| Hair loss | 27.6% | 42.6% |
| Gynecomastia (breast tissue growth) | 20.6% | 32.5% |
| Decreased fertility | 19.0% | 26.2% |
| Restlessness or irritability | 12.9% | 29.1% |
| Depression or low mood | 12.0% | 23.6% |
| Anger or aggression | 9.2% | 21.1% |
All differences above were statistically significant, with small to moderate effect sizes. The data were self-reported and cross-sectional, reflect perceived rather than diagnosed problems, and do not account for dose or other drugs used alongside trenbolone. The survey cannot show that trenbolone caused these problems.
A separate online survey of 282 men who use AAS found that 33% were currently using trenbolone and 55.3% had used it before. After adjusting for age and BMI, a higher trenbolone dose was associated with more verbal aggression (p = 0.045) (Piatkowski et al., Int J Drug Policy 2024).
Side effects and risks
No controlled human trial has measured trenbolone enanthate’s side effects, so their true rates are unknown. The evidence comes from the surveys above, animal studies and case reports.
Suppression of natural hormone production
Like other androgens, trenbolone suppresses the body’s own testosterone. In the rat pilot study, 7.0 mg/week trenbolone enanthate cut serum testosterone by 80% and DHT by 70% within 10 days (Yarrow et al., AJP-Endo 2011). In people, the 1967 acetate study found a fall in urinary 17-ketosteroids at 10 mg every other day (WHO Food Additives Series 23). The claim that trenbolone “doesn’t affect” natural production is not supported by any of this evidence.
Liver
Cholestatic liver injury is widely assumed to be a problem of oral steroids, and trenbolone enanthate is injected. However, a Dutch case report describes a young amateur bodybuilder with jaundice from cholestatic hepatitis (liver inflammation with blocked bile flow). Tests including a liver biopsy made trenbolone enanthate the likely cause. The authors concluded that this kind of liver injury may not be limited to oral steroids (Boks et al., J Sports Sci 2017).
Heart, mood and other case reports
Single-patient reports cannot prove cause or show how often a problem occurs. Reports involving trenbolone, with the ester not always stated, include:
- a 60-year-old long-term steroid user found dead with heart failure and an enlarged heart, with trenbolone found in blood and hair (Gheddar et al., J Anal Toxicol 2021);
- acute psychosis attributed to trenbolone (Bey et al., Therapie 2023).
The surveys above also link trenbolone with more self-reported heart concerns, irritability, low mood and aggression than other AAS use.
Women
In the 1967 acetate study, 10 mg every other day disturbed some women’s menstrual cycles within 2 weeks (WHO Food Additives Series 23). No study has measured virilization (masculinizing changes such as voice deepening or facial hair) in women using trenbolone.
Product quality
Because no licensed human or veterinary trenbolone enanthate product exists in the US, all trenbolone enanthate used by people comes from unregulated sources. No regulator controls its dose, sterility or identity.
Key takeaways
- Never a licensed medicine. Trenbolone enanthate has no FDA approval for people or animals; the only approved trenbolone products are acetate implants for cattle.
- Same hormone, longer ester. About 71% of the ester’s weight is trenbolone. The enanthate slows release from the injection site, but its human half-life has never been measured.
- Evidence is almost entirely from rats. Rat studies found muscle and bone effects with less prostate growth at low doses, but the effects appeared in a uniquely androgen-sensitive muscle, not in ordinary limb muscles.
- It suppresses natural testosterone. In rats, a weekly dose cut testosterone by 80% within 10 days.
- Surveys point to more harms. Men who use trenbolone report more heart, liver, mood and aggression concerns than men using other AAS, though these surveys cannot prove cause.
- Controlled and banned in sport. It is a Schedule III anabolic steroid in the US and prohibited at all times by WADA.
Sources
- Food and Drug Administration. Drugs@FDA: FDA-approved drugs. Drugs@FDA.
- Food and Drug Administration. 21 CFR 522.2476 (trenbolone acetate), 522.2477 (trenbolone acetate and estradiol) and 522.2478 (trenbolone acetate and estradiol benzoate). Electronic Code of Federal Regulations. eCFR 522.2476; eCFR 522.2477; eCFR 522.2478.
- Drug Enforcement Administration. 21 CFR 1300.01 (definition of anabolic steroid) and 21 CFR 1308.13(f) (Schedule III anabolic steroids). eCFR 1300.01; eCFR 1308.13.
- World Anti-Doping Agency. The 2026 Prohibited List, in force January 1, 2026. WADA; published text in Tractatenblad 2026, 25.
- National Center for Biotechnology Information. Trenbolone, PubChem CID 25015; trenbolone acetate, CID 66359; trenbolone enanthate, CID 20112041; trenbolone hexahydrobenzylcarbonate, CID 20055297. PubChem (trenbolone); PubChem (acetate); PubChem (enanthate); PubChem (hexahydrobenzylcarbonate).
- Joint FAO/WHO Expert Committee on Food Additives. Trenbolone acetate. In: Toxicological Evaluation of Certain Veterinary Drug Residues in Food. WHO Food Additives Series 23. Geneva: World Health Organization; 1988. INCHEM.
- Bauer ER, Daxenberger A, Petri T, et al. Characterisation of the affinity of different anabolics and synthetic hormones to the human androgen receptor, human sex hormone binding globulin and to the bovine progestin receptor. APMIS. 2000;108(12):838–846. PubMed.
- Yarrow JF, McCoy SC, Borst SE. Tissue selectivity and potential clinical applications of trenbolone (17beta-hydroxyestra-4,9,11-trien-3-one): a potent anabolic steroid with reduced androgenic and estrogenic activity. Steroids. 2010;75(6):377–389. PubMed.
- Yarrow JF, Conover CF, McCoy SC, et al. 17β-Hydroxyestra-4,9,11-trien-3-one (trenbolone) exhibits tissue selective anabolic activity: effects on muscle, bone, adiposity, hemoglobin, and prostate. Am J Physiol Endocrinol Metab. 2011;300(4):E650–E660. PubMed; PMC.
- McCoy SC, Yarrow JF, Conover CF, et al. 17β-Hydroxyestra-4,9,11-trien-3-one (trenbolone) preserves bone mineral density in skeletally mature orchiectomized rats without prostate enlargement. Bone. 2012;51(4):667–673. PubMed.
- Dalbo VJ, Roberts MD, Mobley CB, et al. Testosterone and trenbolone enanthate increase mature myostatin protein expression despite increasing skeletal muscle hypertrophy and satellite cell number in rodent muscle. Andrologia. 2017;49(3). PubMed.
- Spranger B, Metzler M. Disposition of 17 beta-trenbolone in humans. J Chromatogr. 1991;564(2):485–492. PubMed.
- Krombholz S, Piper T, Lagojda A, et al. The influence of the route of drug administration on the metabolic profile of trenbolone in doping control urine samples. Steroids. 2026;225:109716. PubMed.
- Tretzel L, Thomas A, Geyer H, et al. Use of dried blood spots in doping control analysis of anabolic steroid esters. J Pharm Biomed Anal. 2014;96:21–30. PubMed.
- Krüskemper HL, Morgner KD, Noell G. Clinical pharmacology of trienolones, a group of new anabolically actine aestrane-derivatives (4,9,11-oestratrien-17beta-ol-3-on) [in German]. Arzneimittelforschung. 1967;17(4):449–454. PubMed.
- Bonenti B, Ahmadinejad B, Puljević C, et al. The Trenbolo(g)ne Sandwich: an international study comparing health harms among men who use anabolic-androgenic steroids with and without trenbolone. Drug Alcohol Rev. 2026;45(4):e70162. PubMed; PMC.
- Piatkowski T, De Andrade D, Neumann D, et al. Examining the association between trenbolone, psychological distress, and aggression among males who use anabolic-androgenic steroids. Int J Drug Policy. 2024;134:104636. PubMed.
- Boks MN, Tiebosch AT, van der Waaij LA. A jaundiced bodybuilder: cholestatic hepatitis as side effect of injectable anabolic-androgenic steroids. J Sports Sci. 2017;35(22):2262–2264. PubMed.
- Gheddar L, Pélissier AL, Desfeux J, et al. Testing for trenbolone, an anabolic steroid, in biological fluids and head hair in a post-mortem case. J Anal Toxicol. 2021. PubMed.
- Bey C, Abdelghaffar W, Ach T, et al. A case of acute psychosis triggered by anabolic steroid abuse (trenbolone). Therapie. 2023;78(6):775–778. PubMed.