Clostebol
4-chloro modified testosterone. Unable to aromatize (4-chloro blocks aromatase) and resists 5α-reduction. Very mild anabolic steroid used medically in Italy and Brazil as a topical preparation. Caused a major doping scandal in 2024 when tennis player Jannik Sinner tested positive via contaminated spray.
Mechanism of Action
4-chloro substitution prevents aromatase access and 5α-reductase conversion. Direct AR agonist with moderate selectivity. Available as injectable (acetate/propionate esters), oral, and topical preparations. The topical form (wound-healing cream) achieved notoriety as an inadvertent doping source — even trace skin absorption produces detectable metabolites.
Typical Dosing
⚠ Warning Flags
- •2024 Sinner/Pennetta cases: topical clostebol cream causes doping positives
- •WADA prohibited — banned even in therapeutic topical form for athletes
Effect Profile
Side Effect Profile
Research Studies
Pharmacology of anabolic steroids
Kicman AT. · 2008
Review documents clostebol's mild anabolic profile and inability to aromatize due to 4-chloro modification; notes therapeutic use in wound healing and anemia with favorable safety profile versus most other AAS.
Detection of clostebol and its metabolites in urine by GC/MS following topical application
Donike M, et al. · 1995
Topical application of clostebol cream results in detectable urinary metabolites for 5–7 days — explaining inadvertent doping positive scenarios from therapeutic wound-healing products.