Clostebol (4-chlorotestosterone)
4-chlorotestosterone, a testosterone derivative whose 4-chloro substitution blocks aromatisation and 5-alpha reduction, yielding a mild, non-estrogenic anabolic. Best known today via its acetate ester in topical wound-healing creams (Trofodermin), which have caused several high-profile inadvertent doping positives.
01 Overview
Clostebol is testosterone with a chlorine atom at the 4-position. That single substitution prevents both aromatisation to estrogen and 5-alpha reduction to DHT, so it behaves as a mild, non-estrogenic anabolic with reduced androgenic potency. It was marketed as Steranabol and, as the acetate, in topical antibacterial/wound-healing preparations such as Trofodermin and Nerobolil.
In recent years clostebol has become notorious in anti-doping: because it is present in over-the-counter topical creams and sprays in some countries, athletes have tested positive from trivial contamination, including transfer from a partner or trainer. As an injectable/topical it is not 17-alpha-alkylated and thus not notably hepatotoxic. Systematic human performance data are limited; its profile is inferred from pharmacology and doping-control experience.
02 Mechanism
Androgen receptor agonist. The 4-chloro group sterically and electronically blocks aromatase and 5-alpha-reductase, so it produces neither estrogenic nor DHT-mediated effects, giving a comparatively clean but modest anabolic signal.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Topical cream | 5–15 mg | Transdermal | As acetate in wound-healing preparations; systemic exposure low but doping-relevant. |
| Anecdotal (base/ester) | 100–300 mg/wk | IM | Recreational; mild compound, no controlled dosing data. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Mild lean-mass gainModest non-estrogenic anabolic effect reported anecdotally. | Anecdotal | ||
| Wound healing (topical)Topical acetate preparations promote healing of skin lesions. | Observational | ||
| No estrogenic side effects4-chloro substitution prevents aromatisation, so no gynecomastia from the drug itself. | Preclinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Inadvertent doping positiveTrace amounts from OTC creams or skin contact have triggered anti-doping violations. | Moderate | Notable in athletes | Observational | |
| HPTA suppressionSystemic anabolic doses suppress endogenous testosterone. | Moderate | Dose-dependent | Observational | |
| Androgenic effectsAcne and oily skin at higher systemic doses; virilisation risk in women. | Mild | Dose-dependent | Anecdotal |