Norbolethone (international name norboletone; brand name Genabol) is a synthetic anabolic-androgenic steroid that was never sold as a medicine. It was first synthesized in 1966 and was given to people in 1960s studies of short stature and underweight, but no company ever marketed it (Catlin et al., Rapid Commun Mass Spectrom 2002).
It is best known for its role in sport doping. In 2002 the UCLA Olympic Analytical Laboratory reported finding norbolethone in an athlete’s urine, the first time any doping lab had detected it. A US government investigation later traced it to a chemist who supplied the BALCO laboratory, and it was reportedly the active ingredient of “The Clear” before THG replaced it (Kicman, Br J Pharmacol 2008). The most important fact for readers: there is no modern human data on norbolethone, and the 1960s trial reports are not available as abstracts.
This page summarizes what the early literature, doping-control research and regulators report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Class | Synthetic 19-nor anabolic-androgenic steroid with 13-ethyl and 17α-ethyl groups |
| Other names | Norboletone (INN), Genabol, Wy-3475 (PubChem) |
| Formula / weight | C₂₁H₃₂O₂; 316.5 g/mol (PubChem) |
| Origin | Synthesized 1966; tested in humans in the 1960s; never marketed |
| Studied uses | Short stature and underweight (1960s–1970s studies) |
| Half-life | Not established; no published human pharmacokinetic data found |
| Rat assay potency | Myotrophic 3.44 and androgenic 0.15–0.17 relative to testosterone propionate (injected) |
| US status | Schedule III anabolic steroid, named in the Anabolic Steroid Control Act of 2004 |
| WADA status | Prohibited at all times (S1.1 anabolic androgenic steroids), listed by name as “norboletone” |
What it is
The US legal chemical name of norbolethone is 13β,17α-diethyl-17β-hydroxygon-4-en-3-one (21 CFR 1308.13). Catlin and colleagues describe it as 13-ethyl-17-hydroxy-18,19-dinor-17α-pregn-4-en-3-one, a 19-nor steroid, meaning it lacks the methyl group at carbon 19 that testosterone carries (Catlin et al., 2002). PubChem gives the formula C₂₁H₃₂O₂ and a molecular weight of 316.5 g/mol (PubChem CID 66255).
Two features set it apart from nandrolone (19-nortestosterone):
| Feature | What it means |
|---|---|
| 17α-ethyl group | Alkyl groups at 17α block breakdown of the 17β-hydroxyl group during first pass through the liver, which makes a steroid active when swallowed. The same feature is linked to liver toxicity across this class (Kicman, 2008). |
| 13-ethyl group | An ethyl group replaces the usual methyl at carbon 13 (the “gonane” naming in the legal name reflects this). Progestins built on this skeleton, called 18-methyl-19-nortestosterone, include norgestrel (McRobb et al., 2008). |
Its closest relatives, by their US legal chemical names (21 CFR 1308.13):
| Steroid | Legal chemical name | Difference from norbolethone |
|---|---|---|
| Norbolethone | 13β,17α-diethyl-17β-hydroxygon-4-en-3-one | Reference |
| Norethandrolone | 17α-ethyl-17β-hydroxyestr-4-en-3-one | Methyl instead of ethyl at carbon 13 |
| THG (tetrahydrogestrinone) | 13β,17α-diethyl-17β-hydroxygon-4,9,11-trien-3-one | Two extra double bonds (at 9 and 11) |
In a yeast-based test of androgen receptor activation (a cell assay, not a human study), McRobb and colleagues found that 17α-ethynyl progestins such as norgestrel and gestrinone had notable androgenic activity. Converting the ethynyl group into methyl, ethyl or allyl groups, as in THG and norbolethone, further increased androgenic activity (McRobb et al., J Steroid Biochem Mol Biol 2008). The authors flagged these progestins as the structures with the highest risk of being turned into designer androgens.
How it works in the body
Like other anabolic steroids, norbolethone acts on the androgen receptor. Beyond that, very little is documented:
- Half-life and metabolism in humans: we found no published pharmacokinetic study. Catlin’s lab found norbolethone and “at least one likely metabolite” in an athlete’s urine, but did not report its structure in the abstract (Catlin et al., 2002).
- Route: the abstracts of the 1960s human studies do not state the route or dose. Oral activity would be expected from the 17α-ethyl group, a class property (Kicman, 2008).
Rat potency data
The only potency figures come from the classic rat assay, which compares growth of a small pelvic muscle (the levator ani) with growth of the prostate or seminal vesicles. Kicman’s review, drawing on a 1976 compilation by Potts and colleagues, lists these values for injected norbolethone (Kicman, 2008):
| Steroid (injected) | Myotrophic activity | Androgenic activity | Index |
|---|---|---|---|
| Norbolethone | 3.44 | 0.15–0.17 | 20 |
| Nandrolone decanoate | 3.29–4.92 | 0.41–0.31 | 12.1–10.6 |
| Norethandrolone | 0.77–1.0 | 0.06–0.38 | 2–16 |
All values are relative to testosterone propionate.
About the “20:1” ratio. This index comes from rats, not people. Kicman notes that the levator ani method has been heavily criticized, for example because the seminal vesicles respond more slowly to some androgens, which can distort short tests in favor of the muscle effect (Kicman, 2008). The same index applies to oxandrolone and other steroids that still cause androgenic and hormonal side effects in humans. It should not be read as evidence that norbolethone is “mild” or selective in people.
Former research use
Norbolethone was studied in the 1960s and early 1970s as a drug for poor growth and low body weight (Catlin et al., 2002). The reports appeared in small journals and have no abstracts in PubMed, so their results, doses and sample sizes could not be verified for this page. What the PubMed records show:
| Study | Population or topic | What the record shows |
|---|---|---|
| Albanese et al., N Y State J Med 1968 | Nutritional and metabolic effects in adults, including older adults | Indexed for nitrogen balance, blood glucose, glucose tolerance and lipid metabolism |
| Gogate, Indian J Med Sci 1969 | Idiopathic underweight in adolescents and adults | Title reports efficacy and safety evaluation; indexed for liver function tests and menstruation |
| Gogate, Curr Ther Res Clin Exp 1970 | Linear growth in stunted children and adolescents | Indexed for body height and weight |
| LeVann and Cohn, Int J Clin Pharmacol 1972 | Stunted growth and poorly thriving children | Indexed as placebo-controlled; liver enzyme (AST) measured |
No company brought it to market. We found no primary source explaining why. A 2021 review states that toxicity concerns prevented its marketing, but the paper it cites for this is the 2002 doping report (Tauchen et al., Molecules 2021).
Animal studies
In rats, norbolethone was studied for its ability to protect against the toxic effects of other drugs and chemicals:
- Pretreatment gave some protection against lethal doses of the pesticides parathion and paraoxon in female rats, less than ethylestrenol did for parathion (Robinson et al., J Pharm Sci 1976).
- Studies by Hans Selye’s group reported reduced indomethacin-induced intestinal ulcers and altered digitalis toxicity in rats (Selye, Can J Physiol Pharmacol 1969; Selye et al., Br J Pharmacol 1969).
These are animal findings and say nothing about benefit or safety in humans.
Norbolethone in sport
Norbolethone was one of the first “designer” steroids found in sport, meaning a compound chosen because standard tests did not look for it.
- First detection. Catlin and colleagues identified norbolethone in two urine samples from one athlete by matching mass spectra and chromatography retention times against a reference standard (Catlin et al., 2002). The samples were collected in August 2001 and March 2002 (Kicman, 2008).
- Unusual hormone levels. The same samples had exceptionally low levels of the body’s own steroids. Because no company sold norbolethone, the authors concluded a clandestine source might exist (Catlin et al., 2002).
- The BALCO link. A US government investigation found that a chemist in Champaign, Illinois, made the steroid and that BALCO distributed it. Norbolethone was reputed to be the active ingredient of “The Clear” before THG replaced it (Kicman, 2008). THG itself was identified in 2003 from a used syringe (Catlin et al., Rapid Commun Mass Spectrom 2004).
- Later testing. Doping labs added norbolethone to screens for unknown steroids. A German Sport University method detected it in urine spiked at 50 ng/mL, alongside THG and other designer steroids (Thevis et al., J Mass Spectrom 2005).
Other never-marketed steroids found in sport around the same time include madol (desoxymethyltestosterone) (Kicman, 2008).
Side effects and risks
No human safety data on norbolethone can be checked today. The 1960s trial reports measured liver tests, but their results are not available as abstracts. The risks below are those documented for anabolic steroids as a class (Kicman, 2008).
Liver
Liver toxicity is associated with 17α-alkylated, orally active steroids. Norbolethone carries a 17α-ethyl group. Reported class effects include:
- cholestasis (blocked bile flow) causing jaundice;
- peliosis hepatis (blood-filled cysts in the liver);
- a higher risk of liver tumors.
Hormones and fertility
Anabolic steroids suppress the body’s own sex-hormone production. In men this can cause testicular shrinkage and reduced fertility; Kicman notes that recovery of fertility can take from months to about a year after stopping. The athlete in whom norbolethone was found had exceptionally low levels of his or her own steroids (Catlin et al., 2002), although the paper does not attribute this to a specific cause.
Heart and blood
Class effects include raised LDL cholesterol, lowered HDL cholesterol, raised hematocrit (the share of blood made up of red cells) and an increased risk of heart attack and stroke. Heart muscle damage and sudden cardiac death have also been reported with anabolic steroid misuse.
Virilization in women
In women, anabolic steroids can cause voice deepening, clitoral enlargement, excess body hair and menstrual changes. Voice and clitoral changes may be permanent.
Product quality
Because norbolethone has never been an approved drug, any material in circulation comes from unregulated synthesis, with no assurance of identity, purity or dose. The only documented supply chain is the clandestine one uncovered in the BALCO investigation.
Legal status
- United States. The Anabolic Steroid Control Act of 2004, signed October 22, 2004, named 59 specific substances as Schedule III anabolic steroids, including norbolethone (Public Law 108-358). The changes took effect January 20, 2005 (DEA, Federal Register 2005). It remains listed in Schedule III today (21 CFR 1308.13).
- Sport. WADA lists norboletone by name under S1.1 anabolic androgenic steroids, prohibited at all times, in and out of competition, as a non-Specified Substance (WADA 2026 Prohibited List).
Key takeaways
- A steroid that never became a drug. Norbolethone was synthesized in 1966 and tested in people for short stature and underweight, but it was never marketed.
- Almost no checkable human data. The 1960s trial reports have no abstracts, and no human half-life or modern safety study exists.
- The “20:1” figure is a rat number. It comes from the levator ani assay, a method with well-known flaws, and does not show that the steroid is mild in humans.
- A forerunner of THG. It was found in an athlete’s urine in 2002, was linked to BALCO, and was reportedly the first active ingredient of “The Clear.”
- 17α-alkylated, with class liver risks. Its 17α-ethyl group is the feature associated with liver toxicity in oral anabolic steroids.
- Controlled and banned. It is a named Schedule III steroid in the US and is prohibited at all times by WADA.
Sources
- Catlin DH, Ahrens BD, Kucherova Y. Detection of norbolethone, an anabolic steroid never marketed, in athletes’ urine. Rapid Commun Mass Spectrom. 2002;16(13):1273–1275. PubMed.
- Kicman AT. Pharmacology of anabolic steroids. Br J Pharmacol. 2008;154(3):502–521. PMC.
- National Center for Biotechnology Information. Norbolethone, PubChem CID 66255. PubChem.
- McRobb L, Handelsman DJ, Kazlauskas R, et al. Structure-activity relationships of synthetic progestins in a yeast-based in vitro androgen bioassay. J Steroid Biochem Mol Biol. 2008;110(1-2):39–47. PubMed.
- Albanese AA, Lorenze EJ, Orto LA, et al. Nutritional and metabolic effects of some newer steroids. V. Norbolethone. N Y State J Med. 1968;68(18):2392–2406. PubMed.
- Gogate AN. Evaluation of clinical efficacy and safety of norbolethone in the treatment of idiopathic underweight. Indian J Med Sci. 1969;23(12):648–653. PubMed.
- Gogate AN. Efficacy of norbolethone in stimulating linear growth in stunted children. Curr Ther Res Clin Exp. 1970;12(6):323–332. PubMed.
- LeVann LJ, Cohn RE. Clinical evaluation of norbolethone therapy in stunted growth and poorly thriving children. Int J Clin Pharmacol. 1972;6(1):54–59. PubMed.
- Tauchen J, Jurášek M, Huml L, et al. Medicinal use of testosterone and related steroids revisited. Molecules. 2021;26(4):1032. PMC.
- Robinson CP, Smith PW, McConnell JK, et al. Comparison of protective effects of ethylestrenol, norbolethone, and spironolactone against lethality from acute doses of parathion and paraoxon in female rats. J Pharm Sci. 1976;65(4):595–596. PubMed.
- Selye H. Prevention of indomethacin-induced intestinal ulcers by spironolactone and norbolethone. Can J Physiol Pharmacol. 1969;47(12):981–983. PubMed.
- Selye H, Mécs I, Tamura T. Effect of spironolactone and norbolethone on the toxicity of digitalis compounds in the rat. Br J Pharmacol. 1969;37(2):485–488. PubMed.
- Catlin DH, Sekera MH, Ahrens BD, et al. Tetrahydrogestrinone: discovery, synthesis, and detection in urine. Rapid Commun Mass Spectrom. 2004;18(12):1245–1249. PubMed.
- Thevis M, Geyer H, Mareck U, et al. Screening for unknown synthetic steroids in human urine by liquid chromatography-tandem mass spectrometry. J Mass Spectrom. 2005;40(7):955–962. PubMed.
- Anabolic Steroid Control Act of 2004. Public Law 108-358, 118 Stat. 1661. October 22, 2004. govinfo.
- Drug Enforcement Administration. Implementation of the Anabolic Steroid Control Act of 2004. Federal Register. December 16, 2005;70:74653 (FR Doc 05-23907). Federal Register.
- Code of Federal Regulations. 21 CFR 1308.13, Schedule III. eCFR.
- World Anti-Doping Agency. The 2026 Prohibited List: International Standard. In effect January 1, 2026. WADA 2026 Prohibited List.