Transdermals

Clostebol

Updated · 23 sources · Editorial policy

Clostebol is 4-chlorotestosterone: testosterone with a chlorine atom added at carbon 4. It is an anabolic-androgenic steroid (AAS). Today it is sold mostly as clostebol acetate in creams and sprays (Kintz et al., Clin Chem Lab Med 2025). The best-known product is Trofodermin, an Italian wound cream and spray that also contains the antibiotic neomycin and is sold without a prescription.

Clostebol is best known for a different reason: it is behind a long run of anti-doping cases in which athletes said they were exposed by accident, through a partner, a teammate, a pet or contaminated meat. Controlled studies confirm that brief skin contact with clostebol acetate can produce a positive urine test. We found no controlled trials of clostebol for muscle, strength or performance in people.

This page summarizes what the Italian product label, metabolism and transfer studies, and regulators report. It is for education only and is not medical advice.

Property Detail
Drug class Anabolic-androgenic steroid; 4-chloro derivative of testosterone
Main current product Trofodermin (Italy): clostebol acetate 0.5% + neomycin sulfate 0.5% cream; 5 mg/mL + 5 mg/mL skin spray
Route Topical (skin) for the current product; single oral doses used in human excretion studies
Labeled use (Italy) Abrasions, skin ulcers, burns, infected wounds and slow-healing wounds; 1–2 applications a day
Half-life Not established; we found no published human half-life
Main urinary marker 4-chloro-androst-4-en-3α-ol-17-one (called M1)
US status Not FDA-approved; Schedule III controlled substance
WADA status Prohibited at all times (S1.1 anabolic androgenic steroids), non-Specified

What it is

Clostebol has the formula C₁₉H₂₇ClO₂ and a molecular weight of 322.9 g/mol. Its acetate ester, the form used in products, is C₂₁H₂₉ClO₃ at 364.9 g/mol (PubChem). X-ray crystallography has confirmed the acetate’s structure as a 4-chloro derivative of testosterone with the acetate on the 17β position (Maccaroni et al., Acta Cryst E 2011).

The 4-chloro group is shared by several other steroids, which causes frequent mix-ups. The US Controlled Substances Act list gives their structures (21 CFR 1308.13):

Compound Structure (from 21 CFR 1308.13) How it differs from clostebol
Clostebol 4-chloro-17β-hydroxyandrost-4-en-3-one —
Dehydrochloromethyltestosterone (Oral Turinabol) 4-chloro-17β-hydroxy-17α-methyl-androst-1,4-dien-3-one Adds a 17α-methyl group and a 1,2 double bond

The name “Turinabol” adds to the confusion. A 1966 East German paper used “Turinabol” for 4-chlorotestosterone acetate, that is, clostebol acetate (Schimmelpfennig et al., Acta Biol Med Ger 1966). The better-known oral product is a different compound, covered on our Turinabol page. The WADA list also names methylclostebol and norclostebol as separate prohibited steroids (WADA 2026 Prohibited List).

The Trofodermin label describes clostebol acetate as a testosterone derivative. It attributes the wound effect to the general ability of anabolic steroids to stimulate protein synthesis during granulation and new skin growth (Trofodermin SmPC, AIFA). Anti-doping researchers report that the chlorine at carbon 4 impairs 5α-reductase, the enzyme that turns testosterone into DHT (de la Torre et al., Drug Test Anal 2020).

About ratios and “no aromatization” claims. Online sources often quote an anabolic:androgenic ratio for clostebol and state that it cannot convert to estrogen. We could not find primary human data for either claim, so we do not repeat them here.

Pharmacokinetics

No study we found reports clostebol’s blood half-life, peak levels or bioavailability in people. What is known comes from two places: the product label and anti-doping excretion studies that track metabolites in urine.

Absorption through the skin

The Trofodermin label states that radiolabeled clostebol acetate applied to skin without its outer layer in volunteers showed very little systemic absorption, measured as radioactivity in urine. It also warns that weeks of use over large areas of damaged skin could cause systemic effects such as excess hair growth from heavy absorption of clostebol.

Doping-control studies show that “very little” is still enough to detect:

  • A single 5 mg transdermal dose of clostebol acetate, and even brief contact with the application area, produced urine findings that would count as positive in anti-doping tests (de la Torre et al., Drug Test Anal 2020).
  • In a study of 12 men, 6 received a mixture of four steroids including clostebol acetate on the skin (dissolved in dimethylsulfoxide). The steroids or their metabolites were detectable within hours in some cases and for up to 10–14 days (Gessner et al., Drug Test Anal 2022).

Metabolism and detection windows

Study Design Main finding
de la Torre et al. 2020 Transdermal 5 mg clostebol acetate M1–M4 excreted mainly as glucuronides; M5 mainly as sulfate; route could not be clearly identified
de la Torre et al. 2025 Oral single dose (3 men); transdermal single (1 man) and repeated (3 men, 3 women) 10 metabolites after oral dosing, only 5 after skin use; the M4/M1 ratio helped tell the routes apart
Lu et al. 2015 Oral clostebol, 1 man 14 metabolites; a sulfate metabolite (S1) detectable up to 25 days
Balcells et al. 2016 Oral clostebol, 4 men, urine collected up to 31 days 16 sulfate metabolites; one (S1a) detectable in the last sample of every volunteer

The main screening marker is M1 (4-chloro-androst-4-en-3α-ol-17-one). The 2025 study cautioned that metabolite concentrations vary a lot between people, and that the route of exposure can be estimated but intent cannot.

Approved medical use

Italy: Trofodermin

The Italian medicines agency AIFA lists Trofodermin as a non-prescription medicine for use on the skin, with the ATC code D11AE (androgens for topical use). Its database flags the product as containing a substance prohibited in sport both in and out of competition (AIFA database).

From the Italian summary of product characteristics (Trofodermin SmPC, AIFA):

Item Cream Spray
Strength 500 mg clostebol acetate + 500 mg neomycin sulfate per 100 g 5 mg/mL + 5 mg/mL (0.150 g of each per 30 mL can)
Labeled dose 1–2 thin applications a day, optionally under sterile gauze 1–2 applications a day, optionally under sterile gauze

Labeled uses are abrasions and erosions, skin ulcers (varicose, pressure and traumatic ulcers), cracked nipples and anal fissures, burns, infected wounds, delayed healing, radiation dermatitis and dry, cracked or scaling skin.

United States

Clostebol has no FDA approval; Drugs@FDA lists no clostebol product (Drugs@FDA). It is named as a Schedule III anabolic steroid in federal regulations (21 CFR 1308.13).

Older uses

Clostebol was once also given systemically. For example, the product Steranabol was tested in an 8-week controlled study of 66 patients with chronic hepatitis, mostly alcohol-related (Eberhardt et al., Dtsch Med Wochenschr 1975).

What the research shows

Wound healing

The clinical evidence behind the topical product is old. The Trofodermin clinical papers we found in PubMed date from the late 1960s, in Italian journals, and only their titles are indexed (Molinari and Bolognesi, Minerva Chir 1969). We found no modern randomized trial of clostebol for wounds in people.

In one rat study, the clostebol-neomycin product was used as a reference treatment for skin ulcers (Magalhães et al., Acta Cir Bras 2008). At day 12 it performed no better than saline:

Group (15 rats each) Wound area healed at day 12 Mean repair rate
Saline 77.95% 25.79 mm²/day
Clostebol + neomycin 78.40% 25.42 mm²/day
Test formulation 83.49% 27.38 mm²/day

None of the differences were significant. These are animal data and may not apply to people.

Systemic treatment

The 1975 hepatitis study tested B vitamins and clostebol over 8 weeks. In chronic active hepatitis, treated and untreated patients did not differ. In fatty liver hepatitis, the untreated group actually did better, which the authors linked to reduced drinking during hospital stay (Eberhardt et al., Dtsch Med Wochenschr 1975).

Muscle and performance

We found no controlled human trials of clostebol for muscle mass, strength or athletic performance. Any claims about its effects on muscle in people are not backed by published trial data.

Clostebol in anti-doping

How inadvertent exposure happens

Clostebol acetate is sold over the counter as a cream or spray in several countries, and laboratories have become much more sensitive. Together these have driven a rise in clostebol findings, especially in Italy (de la Torre et al., Drug Test Anal 2020; Kintz et al., Clin Chem Lab Med 2025). Documented and proposed routes of exposure include:

  • Contaminated meat. In a feeding experiment, volunteers who ate 100 g of meat containing 1 mg or 0.1 mg of clostebol acetate both excreted a clostebol metabolite (Debruyckere et al., Clin Chem 1992).
  • Sexual contact. A 2004 report described athletes whose positive tests were attributed to intercourse with a partner using clostebol (Pereira et al., Clin Chem 2004).
  • Treating a pet. A canoeist sprayed Trofodermin on her dog’s paws twice daily for 7 days. About 1.5 days after the last dose her urine contained about 1.7 ng/mL of M1. Clostebol acetate was found in her hair (52–78 pg/mg, depending on the segment) and at a much higher level in the dog’s fur (980 pg/mg). The Court of Arbitration for Sport found an anti-doping rule violation, but with no fault (Pokrywka et al., Front Sports Act Living 2024).
  • Contaminated objects. A 2026 commentary proposed delayed transfer from textiles, equipment or surfaces as an explanation for very low findings (about 20–500 pg/mL of M1). The authors note that no controlled studies of this route exist yet (Salomone and Kintz, Clin Chem Lab Med 2026).

Direct vs indirect exposure

A 2025 systematic review pooled 7 papers covering 32 people with skin or mucous-membrane exposure (Menditto et al., Clin Chem Lab Med 2025):

Exposure Median urinary M1 Range Interquartile range
Indirect contact 0.5 ng/mL 0.086–4.0 ng/mL 0.5–0.9 ng/mL
Direct contact 8.1 ng/mL 1.0–36.6 ng/mL 2.8–22.0 ng/mL

The difference was significant (p = 0.005). Low concentrations fit contamination, but they can also be the tail end of deliberate use, which is why researchers have proposed a reporting level for M1 and testing of other samples such as hair (de la Torre et al., Drug Test Anal 2020; Kintz et al., Clin Chem Lab Med 2025).

Under the WADA rules, clostebol is prohibited at all times and is a non-Specified Substance (WADA 2026 Prohibited List).

Side effects and risks

Topical product

The Trofodermin label lists the following (Trofodermin SmPC, AIFA):

  • Sensitization. Prolonged use of topical products can cause allergic skin reactions. The cream’s lanolin and parabens can cause contact dermatitis and allergic reactions.
  • Systemic androgen effects. Use over several weeks on large areas of damaged skin may cause systemic effects such as hypertrichosis (excess hair growth).
  • Neomycin. Because neomycin can damage hearing and the kidneys, prolonged use on large damaged areas is discouraged. Combining it with other topical aminoglycoside antibiotics may raise the risk of sensitization.
  • Continuous use. The label says to avoid continuous use, especially in very young children. In pregnancy and breastfeeding, it should be used only when truly needed.

The only labeled contraindication is hypersensitivity to the ingredients.

Systemic use

No modern clinical study has measured clostebol’s systemic side effects, such as suppression of natural testosterone, cholesterol changes or liver effects. For what these risks look like with better-studied steroids, see our testosterone cypionate and Anavar (oxandrolone) pages.

  • United States: Schedule III, named in 21 CFR 1308.13(f), which also covers its salts, esters and ethers (21 CFR 1308.13).
  • Sport: prohibited at all times under WADA class S1.1 (WADA 2026 Prohibited List).
  • Food animals: clostebol acetate use in cattle fattening is strictly forbidden in the European Union. Illegal use has been documented, and in cattle its metabolites were detectable for 1.5 months after an intramuscular dose (Le Bizec et al., Clin Chem 1998).

Key takeaways

  • A chlorinated testosterone. Clostebol is testosterone with a chlorine at carbon 4. It is not the same drug as Oral Turinabol, although the names have overlapped historically.
  • Mainly a wound product today. Its main current product is Trofodermin, an Italian non-prescription cream and spray that combines clostebol acetate with neomycin.
  • Thin clinical evidence. The wound-healing studies date from around 1970. We found no modern human trials, and no human trials at all for muscle or performance.
  • Small skin exposures are detectable. A single 5 mg skin dose or brief contact can produce a positive anti-doping test. Metabolites from skin exposure can stay detectable for up to about 2 weeks.
  • Indirect contact usually leaves lower levels. Median urinary M1 was 0.5 ng/mL after indirect contact vs 8.1 ng/mL after direct application, but low levels alone cannot prove how exposure happened.
  • Controlled and banned in sport. Clostebol is Schedule III in the US, has no FDA approval, and is prohibited at all times by WADA.

Sources

  1. National Center for Biotechnology Information. PubChem Compound Summary: Clostebol (CID 68947) and Clostebol acetate (CID 13327). PubChem; PubChem.
  2. Maccaroni E, Mele A, Del Rosso R, Malpezzi L. Clostebol acetate. Acta Crystallogr Sect E Struct Rep Online. 2011;67(Pt 8):o1952–o1953. PubMed.
  3. Laboratorio Farmaceutico S.I.T. Trofodermin 500 mg/100 g + 500 mg/100 g crema; Trofodermin 5 mg/ml + 5 mg/ml spray cutaneo, sospensione. Riassunto delle caratteristiche del prodotto (Italian SmPC), made available by AIFA June 11, 2016. AIFA.
  4. Agenzia Italiana del Farmaco. Banca dati farmaci: Trofodermin. AIFA.
  5. Schimmelpfennig W, Hagemann I, Korte G. On the influence of 4-chlorotestosterone acetate (Turinabol) on acute renal failure in rats [in German]. Acta Biol Med Ger. 1966;17(3):298–306. PubMed.
  6. Eberhardt G, Möhr J, Oehlert W, Schmidt E, Schmidt FW, Vondrásek P. Controlled study of the therapeutic effect of B vitamins and an anabolic steroid in chronic hepatitis [in German]. Dtsch Med Wochenschr. 1975;100(41):2074–2082. PubMed.
  7. Molinari L, Bolognesi L. Clinical observations on cutaneous cicatrization with F.I. 6321-N (trofodermin) [in Italian]. Minerva Chir. 1969;24(3):177–187. PubMed.
  8. Magalhães MS, Fechine FV, Macedo RN, et al. Effect of a combination of medium chain triglycerides, linoleic acid, soy lecithin and vitamins A and E on wound healing in rats. Acta Cir Bras. 2008;23(3):262–269. PubMed.
  9. de la Torre X, Colamonici C, Iannone M, et al. Detection of clostebol in sports: accidental doping? Drug Test Anal. 2020;12(11-12):1561–1569. PubMed.
  10. de la Torre X, Colamonici C, Martínez Brito D, de Oca Porto RM, Botrè F. Clostebol metabolism by different routes of administration: selection of diagnostic urinary markers. Drug Test Anal. 2025;17(12):2399–2410. PubMed.
  11. Lu J, Fernández-Álvarez M, Yang S, et al. New clostebol metabolites in human urine by liquid chromatography time-of-flight tandem mass spectrometry and their application for doping control. J Mass Spectrom. 2015;50(1):191–197. PubMed.
  12. Balcells G, Pozo OJ, Garrostas L, et al. Detection and characterization of clostebol sulfate metabolites in Caucasian population. J Chromatogr B Analyt Technol Biomed Life Sci. 2016;1022:54–63. PubMed.
  13. Gessner L, Thevis M, Rothschild MA, Jübner M. Detectability of oxandrolone, metandienone, clostebol and dehydrochloromethyltestosterone in urine after transdermal application. Drug Test Anal. 2022;14(10):1744–1761. PubMed.
  14. Menditto VG, Rossetti G, Ferrarini A, et al. Clostebol detection after transdermal and transmucosal contact. A systematic review. Clin Chem Lab Med. 2025;63(8):1472–1480. PubMed.
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  16. Pereira HM, Marques MA, Talhas IB, Aquino Neto FR. Incidental clostebol contamination in athletes after sexual intercourse. Clin Chem. 2004;50(2):456–457. PubMed.
  17. Pokrywka A, Sitkowski D, Surała O, Gheddar L, Kintz P. Case Report: A case study of positive doping control by animal-to-human drug transfer after an athlete administered medicine in spray format, containing clostebol acetate, to a pet dog. Front Sports Act Living. 2024;6:1480373. PubMed; PMC.
  18. Kintz P, Gheddar L, Pichini S, Plebani M, Salomone A. Clostebol and sport: about controversies involving contamination vs. doping offence. Clin Chem Lab Med. 2025;63(2):258–261. PubMed.
  19. Salomone A, Kintz P. Ultra-trace urinary clostebol findings: should delayed transfer from contaminated objects be considered? Clin Chem Lab Med. Published online August 28, 2026. PubMed.
  20. Le Bizec B, Montrade MP, Monteau F, Gaudin I, Andre F. 4-Chlorotestosterone acetate metabolites in cattle after intramuscular and oral administrations. Clin Chem. 1998;44(5):973–984. PubMed.
  21. World Anti-Doping Agency. The 2026 Prohibited List (in effect January 1, 2026). WADA 2026 Prohibited List.
  22. Code of Federal Regulations. 21 CFR 1308.13, Schedule III. 21 CFR 1308.13.
  23. US Food and Drug Administration. Drugs@FDA: FDA-Approved Drugs (database search for clostebol). Drugs@FDA.