Injectables

Equipoise (Boldenone Undecylenate)

Updated · 24 sources · Editorial policy

Equipoise is a veterinary brand of boldenone undecylenate, a long-acting injectable anabolic steroid. In the US its only approval is for horses, “as an aid for treating debilitated horses” that need to gain weight or improve their coat or general condition. Zoetis is the current sponsor.

Boldenone is not approved for human use. Even so, it is one of the steroids most often detected in people who use anabolic-androgenic steroids (AAS) outside medicine in the US (Pope et al., Endocr Rev 2014). No controlled trial has ever tested boldenone in people. What is known about it in humans comes from drug-testing studies, case reports and one small observational study.

This page summarizes what the veterinary label, the regulators and the limited research report. It is for education only and is not medical advice.

Property Detail
Drug class Injectable anabolic-androgenic steroid; ester of boldenone, a testosterone derivative
Brand / approval Equipoise (Zoetis), NADA 34-705; approved for horses only
Human approval None in the US
Route Intramuscular injection
Strengths 50 mg/mL in sesame oil (label); the federal regulation also lists 25 mg/mL
Labeled dose (horses) 0.5 mg per pound body weight IM, repeatable at 3-week intervals
Boldenone content About 63% of the ester’s weight (50 mg ester ≈ 32 mg boldenone)
Half-life No human data; elimination half-life ≈ 123 h (about 5 days) in horses
US schedule Controlled substance, Schedule III
WADA status Prohibited at all times (S1.1 anabolic agents)

What it is

Boldenone is testosterone with one extra double bond, between carbons 1 and 2 of the A-ring. Its chemical name is 17β-hydroxyandrosta-1,4-dien-3-one (21 CFR 1308.13). The same A-ring appears in other steroids in this library:

Steroid Relation to boldenone
Testosterone Boldenone without the 1,2 double bond
Methandienone (Dianabol) Boldenone plus a 17α-methyl group, which makes it orally active
Dihydroboldenone (DHB, 1-testosterone) The 5α-reduced form: 17β-hydroxy-5α-androst-1-en-3-one
Boldione The 17-keto form, androsta-1,4-diene-3,17-dione

These names come from the WADA Prohibited List, which lists each of them separately (WADA 2026 List, official Dutch publication). Unlike methandienone, boldenone has no 17α-methyl group. It is used as an injectable ester rather than as an oral tablet.

The undecylenate ester is an 11-carbon fatty acid chain attached at the 17β position. According to PubChem, the ester has the formula C₃₀H₄₄O₃ and a molecular weight of 452.7 g/mol, against 286.4 g/mol for boldenone itself (PubChem: boldenone undecylenate; PubChem: boldenone). So about 63% of each labeled milligram is boldenone. As with testosterone esters, blood esterases cleave the ester and release the active steroid; the ester’s length mainly sets how slowly it leaves the oil depot (Kicman, Br J Pharmacol 2008).

The Equipoise label describes it as “a steroid ester possessing marked anabolic properties and a minimal amount of androgenic activity.” It adds that laboratory-animal studies showed “a certain degree of androgenic activity” (Equipoise label). The label gives no numbers for either.

About anabolic:androgenic ratios. Online sources often quote a “100:50” ratio for boldenone. We could not trace this figure to a published assay, so we do not repeat it. The only primary statement is the qualitative one on the veterinary label.

Small amounts occur naturally

Boldenone is not purely synthetic. Human liver cells grown in the lab convert testosterone into small amounts of boldenone (Fabregat et al., Steroids 2015). Low concentrations of boldenone and its metabolites have also been found in urine from people who had not taken it (Wu et al., J Pharm Biomed Anal 2015). In uncastrated male horses, the testis makes boldenone from testosterone and androstenedione (Viljanto et al., Steroids 2019).

This matters for drug testing. When boldenone is found at low levels in an athlete’s urine, labs use isotope-ratio mass spectrometry to tell a natural origin from an injected one (Gómez et al., J Steroid Biochem Mol Biol 2012).

How it behaves in the body

There are no pharmacokinetic studies of boldenone undecylenate in humans. The best-characterized data come from horses.

In a study at the University of Pennsylvania, horses received boldenone at 1.1 mg/kg IM, which equals the labeled 0.5 mg per pound. Blood was sampled for up to 64 days (Soma et al., J Vet Pharmacol Ther 2007):

Measure (horses) Result
Absorption half-life (median) 8.5 h
Elimination half-life (median) 123.0 h (≈ 5.1 days)
Peak plasma concentration (mean) 1,127.8 pg/mL
Total exposure (AUC) 274.8 ng·h/mL

Horse data cannot be transferred directly to people. The 3-week dosing interval on the equine label fits a slow-release depot, but the human half-life has never been measured.

What has been measured in people is how boldenone is broken down. In a study with 3 men and 3 women, each took a single 30 mg oral dose of boldenone (not the injectable ester). Unchanged boldenone and its metabolite 5β-androst-1-en-17β-ol-3-one, often called BM1, appeared in urine; in most volunteers BM1 levels were higher than boldenone’s. The 17α-epimer of boldenone was excreted in small amounts, and the pattern did not differ between men and women (Wu et al., J Pharm Biomed Anal 2015). In a separate excretion study in one volunteer, sulfate-conjugated metabolites made up less than 1% of the dose (Gómez et al. 2012).

How much boldenone is converted to estrogen in people has not been measured. In human placental tissue in the lab, the closely related boldione is converted both to estrogens and to boldenone (Milewich et al., J Steroid Biochem 1981). That shows the 1,4-diene ring can be a substrate for aromatase (the enzyme that makes estrogen from androgens), but it does not tell us how much estradiol forms after a boldenone injection.

Approved veterinary use

Boldenone undecylenate is approved only for horses. The federal regulation and label set out the terms (21 CFR 522.204; Equipoise label):

  • Indication: an aid for treating debilitated horses when an improvement in weight, hair coat or general physical condition is desired.
  • Dose: 0.5 mg per pound body weight by intramuscular injection; treatment may be repeated at 3-week intervals. The label says most horses respond to one or two treatments.
  • Place in therapy: adjunctive only, alongside specific treatment for disease, surgery or injury. The label states it “is not a substitute for a well-balanced diet.”
  • Limits: not for horses intended for human consumption, and veterinary prescription only.

The equine regulation dates back to 1975. A 1996 edition already restricted the drug to horses and advised against use in stallions and pregnant mares, because effectiveness in them had not been established and the drug had not been shown to be free of birth-defect risk (21 CFR 522.204, 1996 edition). In 2005, FDA approved revised labeling under NADA 34-705, then held by Fort Dodge Animal Health, with a revised indication and food-safety warning (70 FR 70997). The current sponsor code in the regulation belongs to Zoetis (21 CFR 510.600).

The Association of Racing Commissioners International, the International Federation of Horseracing Authorities and the Fédération Equestre Internationale prohibit the use of anabolic steroids in horse racing and equestrian sport (Dirikolu and Lehner, J Vet Pharmacol Ther 2023).

What the research shows

In horses

The label reports that in clinical trials at the recommended dose, Equipoise “had a marked anabolic effect in debilitated horses.” Appetite and vigor improved, and musculature and coat looked better. The label does not give trial size, design or numeric results. A 2005 FDA notice states that the revised labeling did not require review of new safety or effectiveness data (70 FR 70997). A 2023 veterinary review notes that only minimal pharmacodynamic studies of anabolic steroids have been done in horses, and that their use rests largely on practitioners’ opinions (Dirikolu and Lehner 2023).

In humans

No randomized or controlled trial has tested boldenone for muscle, strength, body composition or any medical condition in people. The human literature consists of:

  • metabolism and drug-testing studies in a handful of volunteers (described above);
  • case reports in people who used boldenone along with other drugs;
  • one small observational study of bodybuilders (see Kidneys below).

Claims that boldenone builds “lean, dry” muscle, raises appetite or improves endurance in people come from user reports, not from trials. The effects of AAS as a class on muscle are well established with testosterone (see Testosterone cypionate). Whether boldenone differs from testosterone in any meaningful way in humans has not been studied.

In laboratory animals

Most published boldenone toxicology is in rats and rabbits, often at high doses. In one rabbit study, animals received 5 mg/kg boldenone undecylenate IM every 3 weeks for 1–3 injections. Serum urea and creatinine rose, and kidney tissue showed glomerulosclerosis (scarring of the kidney’s filtering units) that worsened with more injections (Alm-Eldeen and Tousson, Hum Exp Toxicol 2012). The same regimen raised the liver enzymes ALT and AST in rabbits (Tousson et al., Toxicol Ind Health 2016). These are animal results and do not establish the same effects or doses in people.

Side effects and risks

Boldenone-specific human safety data are limited to case reports and one small study. Most of what is known about risk comes from AAS use as a class.

What the veterinary label reports

In horses, the label lists androgenic effects, described as “over aggressiveness,” in a few animals. These may persist for 6–8 weeks, and no further injections should be given if they appear. The label also says the drug should not be used in stallions or pregnant mares because effects on them and possible birth defects have not been studied (Equipoise label).

Kidneys

  • Case report. A 37-year-old man was referred for a high creatinine and low estimated kidney function (eGFR) with no other signs of kidney disease. The raised creatinine was linked to boldenone use. The authors point out that creatinine can overstate kidney damage, so a high value alone may lead to a misdiagnosis (Winnett et al., Nephrol Dial Transplant 2011).
  • Observational study. A Turkish study scanned the kidneys of 22 bodybuilders in three groups. One group of 7 used testosterone enanthate, nandrolone decanoate and boldenone undecylenate for 16 weeks. That group had larger kidneys, a thicker renal cortex that was more echogenic (brighter on ultrasound), and higher blood urea nitrogen and creatinine than the other two groups. Urine microalbumin was normal in all groups (Kantarci et al., J Sports Med Phys Fitness 2018).

The study was small and not randomized. The boldenone group also used other steroids and ate more protein, so it cannot isolate boldenone’s effect.

Heart

A 39-year-old weightlifter developed fulminant heart failure with a left ventricular ejection fraction (the share of blood pumped out with each beat) of about 15%. His dilated cardiomyopathy was attributed to testosterone and boldenone use in the previous 3 months (White et al., Can J Cardiol 2018). A single case cannot prove cause.

At the class level, the Endocrine Society lists cardiomyopathy, atherosclerotic disease, polycythemia (too many red blood cells) and lower HDL (“good”) cholesterol among well-recognized AAS risks (Pope et al., Endocr Rev 2014).

Hormonal suppression and fertility

The label says that in laboratory animals Equipoise “does not have marked antigonadotropic properties.” That is an animal statement, and it has not been tested in men. The Endocrine Society statement lists suppression of the hypothalamic-pituitary-testicular axis, and hypogonadism after stopping, among the well-recognized serious effects of AAS use. It names infertility, low sperm counts, testicular atrophy and gynecomastia (breast tissue growth in men) among the effects seen in users (Pope et al. 2014). There is no evidence that boldenone is an exception.

Who should not use it

Boldenone is not a human medicine, so there is no human label with contraindications or dosing. The equine label itself warns against use in pregnant animals because effects on offspring have not been studied.

  • US. Boldenone, including its esters, is a Schedule III controlled substance (21 CFR 1308.13). The veterinary product requires a veterinarian’s order, and its labeled use is limited to horses.
  • Sport. WADA’s 2026 Prohibited List names boldenone under S1.1 anabolic androgenic steroids. S1 substances are prohibited in and out of competition and are not “specified” substances (WADA 2026 List, official Dutch publication).
  • Food animals. In livestock, boldenone and its metabolites are monitored as markers of illegal growth-promoter use (De Brabander et al., Food Addit Contam 2004).

The Endocrine Society statement notes that, although boldenone is a veterinary steroid not approved for human use, it is among the most often detected drugs in illicit AAS users in the US (Pope et al. 2014). Product sold outside the regulated veterinary supply is not checked for dose, sterility or identity.

Key takeaways

  • A horse drug only. Equipoise is approved in the US only to help debilitated horses regain weight and condition, at 0.5 mg per pound, repeatable at 3-week intervals.
  • No human trials. There are no controlled studies of boldenone in people, so claims about its effects in humans rest on user reports.
  • About 63% boldenone by weight. The undecylenate ester slows release; in horses the elimination half-life is about 5 days. Human pharmacokinetics are unknown.
  • Kidney and heart signals come from case reports. A raised creatinine and a case of heart failure have been linked to boldenone, but the evidence is weak and confounded by other drug use.
  • Expect class effects. Nothing shows boldenone avoids the suppression of natural testosterone, fertility effects or cardiovascular risks seen with AAS in general.
  • Controlled and banned in sport. It is Schedule III in the US and prohibited at all times by WADA.

Sources

  1. Fort Dodge Animal Health (now Zoetis). Equipoise (boldenone undecylenate injection) package insert, NADA 34-705, revised July 2005. Drugs.com archived copy.
  2. 21 CFR 522.204. Boldenone. Electronic Code of Federal Regulations. eCFR.
  3. 21 CFR 522.204. Boldenone undecylenate injection. Code of Federal Regulations, April 1, 1996 edition. govinfo.
  4. Food and Drug Administration. Implantation or injectable dosage form new animal drugs; boldenone. Federal Register. November 25, 2005;70:70997–70998 (FR Doc 05-23295). govinfo.
  5. 21 CFR 510.600. Names, addresses, and drug labeler codes of sponsors of approved applications. eCFR.
  6. 21 CFR 1308.13. Schedule III. eCFR.
  7. World Anti-Doping Agency. The 2026 Prohibited List, as published in Tractatenblad van het Koninkrijk der Nederlanden. 2026;25. officielebekendmakingen.nl.
  8. National Center for Biotechnology Information. Boldenone undecylenate, PubChem CID 11954310. PubChem.
  9. National Center for Biotechnology Information. Boldenone, PubChem CID 13308. PubChem.
  10. Kicman AT. Pharmacology of anabolic steroids. Br J Pharmacol. 2008;154(3):502–521. PubMed.
  11. Soma LR, Uboh CE, Guan F, McDonnell S, Pack J. Pharmacokinetics of boldenone and stanozolol and the results of quantification of anabolic and androgenic steroids in race horses and nonrace horses. J Vet Pharmacol Ther. 2007;30(2):101–108. PubMed.
  12. Wu X, Gao F, Zhang W, Ni J. Metabolism study of boldenone in human urine by gas chromatography-tandem mass spectrometry. J Pharm Biomed Anal. 2015;115:570–575. PubMed.
  13. Gómez C, Pozo OJ, Geyer H, et al. New potential markers for the detection of boldenone misuse. J Steroid Biochem Mol Biol. 2012;132(3-5):239–246. PubMed.
  14. Fabregat A, Marcos J, Ventura R, et al. Formation of Δ(1) and Δ(6) testosterone metabolites by human hepatocytes. Steroids. 2015;95:66–72. PubMed.
  15. Viljanto MJ, Kicman AT, Walker CJ, et al. Elucidation of the biosynthetic pathways of boldenone in the equine testis. Steroids. 2019;146:79–91. PubMed.
  16. Milewich L, Bradfield DJ, Coe LD, Masters BS, MacDonald PC. Metabolism of 1,4-androstadiene-3,17-dione by human placental microsomes. Enzyme properties and kinetic parameters in the formation of estrogens and 17 beta-hydroxy-1,4-androstadien-3-one. J Steroid Biochem. 1981;14(11):1115–1125. PubMed.
  17. Dirikolu L, Lehner AF. A review of current chemistry, pharmacology, and regulation of endogenous anabolic steroids testosterone, boldenone, and nandrolone in horses. J Vet Pharmacol Ther. 2023;46(4):201–217. PubMed.
  18. Winnett G, Cranfield L, Almond M. Apparent renal disease due to elevated creatinine levels associated with the use of boldenone. Nephrol Dial Transplant. 2011;26(2):744–747. PubMed.
  19. Kantarci UH, Punduk Z, Senarslan O, Dirik A. Evaluation of anabolic steroid induced renal damage with sonography in bodybuilders. J Sports Med Phys Fitness. 2018;58(11):1681–1687. PubMed.
  20. White M, Brennan E, Mi Ren KY, et al. Anabolic androgenic steroid use as a cause of fulminant heart failure. Can J Cardiol. 2018;34(10):1369.e1–1369.e3. PubMed.
  21. Alm-Eldeen A, Tousson E. Deterioration of glomerular endothelial surface layer and the alteration in the renal function after a growth promoter boldenone injection in rabbits. Hum Exp Toxicol. 2012;31(5):465–472. PubMed.
  22. Tousson E, El-Moghazy M, Massoud A, et al. Physiological and biochemical changes after boldenone injection in adult rabbits. Toxicol Ind Health. 2016;32(1):177–182. PubMed.
  23. De Brabander HF, Poelmans S, Schilt R, et al. Presence and metabolism of the anabolic steroid boldenone in various animal species: a review. Food Addit Contam. 2004;21(6):515–525. PubMed.
  24. Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375. PubMed.