D tier · weak
Boldenone undecylenate is approved only as a veterinary drug for debilitated horses, its brief human marketing as Parenabol ended in the late 1970s, and the modern literature is almost entirely doping-control analytics and residue toxicology rather than human safety or efficacy research.
boldenone undecylenate
Boldenone undecylenate is licensed in the United States solely as a veterinary product for horses, where the labelled use is as an aid in treating debilitated animals when improvement in weight, haircoat or general condition is desired. It was briefly marketed for humans as Parenabol in the 1960s and discontinued in the late 1970s, and no controlled human efficacy or safety trial has been published since, leaving the compound essentially uncharacterised in people.
the explanation
Boldenone is a horse drug. It is legally sold in the US only through veterinarians for run-down horses, it was dropped from human medicine in the 1970s, and nobody has run a proper human trial on it since.
regulatory status
US veterinary prescription drug (horses only); never currently approved for humans; DEA Schedule III
Equipoise (boldenone undecylenate, Zoetis) is labelled for horses as an aid in treating debilitated horses, with federal law restricting use to by or on the order of a licensed veterinarian and prohibiting use in horses intended for human consumption. The compound was introduced for human clinical use as Parenabol in the 1960s and discontinued for humans in the late 1970s; it is not FDA-approved for humans. Boldenone is named individually in the DEA schedules as 17-beta-hydroxyandrost-1,4-diene-3-one, Schedule III, and is Schedule IV in Canada. Prohibited in sport.
how it works · proposed mechanism
Boldenone is a conventional androgen receptor agonist whose distinguishing features are its low aromatisation efficiency and its very long ester chain.
Delta-1 modification of testosterone
The added 1,2 double bond in the A-ring alters enzyme handling relative to testosterone without changing the fundamental androgen receptor agonism. The result described in the literature is a molecule with androgenic and anabolic activity but reduced aromatase conversion efficiency.
Long-chain undecylenate depot
The eleven-carbon unsaturated ester gives one of the slowest release profiles among injectable AAS, with a reported intramuscular half-life around 14 days. Long metabolite persistence is the basis of extended doping-control detection windows.
Endogenous background complicates detection
Low concentrations of boldenone occur naturally in human urine. A forensic study of twenty unexposed young males measured a mean urinary boldenone level of 3.19 ± 1.65 ng/ml (range 0.37–6.02), which is why analytical methods must discriminate endogenous from exogenous origin.
what’s reported
evidence shape
6 sourcesThe composition of the cited literature by study type. This describes the shape of the evidence, not its quality — and it does not by itself set the grade.
⚠ the catch
Boldenone's published literature is dominated by analytical chemistry and food-residue toxicology rather than human pharmacology, so the compound has effectively no human safety data of its own. Everything that can honestly be said about its risk in people is extrapolated from the anabolic androgenic steroid class as a whole.
key published findings
- Regulatory (Zoetis/FDA veterinary labelling): Equipoise is indicated only as an aid for treating debilitated horses when an improvement in weight, haircoat or general physical condition is desired; federal law restricts it to veterinary order and the label prohibits use in horses intended for human consumption.
- Human forensic/observational (Park 2019, J Pharm Biomed Anal): urinary boldenone was measurable in twenty young males with no boldenone exposure at a mean of 3.19 ± 1.65 ng/ml (range 0.37–6.02 ng/ml), establishing an endogenous baseline in humans.
- Analytical/preclinical (Blokland 2007, Anal Chim Acta): analysis of approximately 10,000 bovine urine samples established that unconjugated beta-boldenone and alpha-boldenone conjugates indicate endogenous origin, while no evidence was obtained that conjugated beta-boldenone can be endogenous.
- Regulatory (DEA schedules): boldenone is named individually as 17-beta-hydroxyandrost-1,4-diene-3-one under Schedule III, and boldenone undecylenate holds CAS 13103-34-9 with formula C30H44O3 and molar mass 452.7 (PubChem, verified).
- Class-level human observational (Baggish 2017, Circulation): 86 long-term AAS users versus 54 non-users showed LVEF 52 ± 11% versus 63 ± 8% and greater coronary plaque volume, with lifetime AAS dose strongly associated with coronary atherosclerotic burden.
limitations of the evidence
- There is no published controlled human trial of boldenone undecylenate for any endpoint, so no compound-specific efficacy or safety estimate can be given.
- The 14-day half-life figure and most human pharmacological description come from secondary sources rather than primary human PK studies.
- Endogenous human boldenone production means some analytical findings in the literature reflect natural background rather than exposure, requiring careful interpretation.
documented safety signals
- No human safety monitoring framework exists at all: the compound is a veterinary product, so there is no human prescribing information, no adverse-event labelling and no postmarketing surveillance.
- HPG-axis suppression with reduced LH and FSH, testicular atrophy, impaired spermatogenesis and infertility, expected as a class effect and documented in AAS cohorts (Rasmussen 2016: current users showed severely decreased AMH and inhibin B indicating impaired spermatogenesis).
- Persistent post-cessation hypogonadism: 27.2% of former AAS users were below the lower total testosterone reference limit a mean 2.5 years after cessation versus 0% of controls, with 27.3% reporting erectile dysfunction and 40.1% decreased libido (Rasmussen 2016).
- Adverse lipid shift with marked HDL suppression documented across AAS users (Hartgens 2004: HDL-C 1.08 to 0.43 mmol/l).
- Polycythaemia and raised haematocrit, a general androgen class effect that increases blood viscosity.
- Cardiomyopathy and accelerated coronary atherosclerosis in long-term AAS users (Baggish 2017), with reduced left ventricular systolic and diastolic function.
- Oestrogenic effects including gynaecomastia remain possible because boldenone is aromatisable, albeit less efficiently than testosterone.
- Very long detection window and slow clearance mean adverse effects, once established, resolve slowly after exposure stops.
- Injection-related infection, abscess and bloodborne virus exposure documented in people injecting image- and performance-enhancing drugs (Hope 2015).
- Because the only legal supply is veterinary, human-grade sterility, concentration accuracy and excipient safety are not assured; product-testing data in AAS cohorts found only 47% of submitted samples contained the labelled substance (HAARLEM).
identity
| full name | Boldenone undecylenate (veterinary anabolic androgenic steroid) |
| category | Anabolic & Androgenic |
| modality | steroid |
| formula | C30H44O3 |
| molar mass | 452.7 g/mol |
| cas | 13103-34-9 |
| half-life | Reported at approximately 14 days by intramuscular injection. No human pharmacokinetic trial has been published; the figure derives from secondary literature and veterinary data. |
laboratory handling
| storage | Veterinary labelling specifies storage at controlled room temperature protected from light. There is no human-use storage labelling because no human product exists. |
| solubility | Practically insoluble in water. The undecylenate ester is highly lipophilic and oil-soluble, formulated in the veterinary product as a solution in a vegetable oil vehicle. |
| co-studied with | Reference note only, not guidance: boldenone appears in observational AAS cohorts almost exclusively as one component of multi-agent regimens, so no observational dataset isolates its independent contribution to any outcome. |
Handling information describes laboratory practice for a research reagent. It is not a preparation guide for use in humans.
the receipts
6 citedZoetis / Drugs.com Veterinary · 2025 · official
Federal Register (US FDA) · 2005 · official
US DEA Diversion Control Division · 2025 · official
Journal of Pharmaceutical and Biomedical Analysis · 2019 · observational
Analytica Chimica Acta · 2007 · preclinical
Endocrine Reviews · 2014 · reviews
others in Anabolic & Androgenic