Norclostebol Acetate
The acetate ester of norclostebol (4-chloro-19-nortestosterone), a 19-nor/chlorinated injectable androgen used historically in some European and veterinary products. A relative of clostebol and nandrolone; a recurring anti-doping finding, including via contamination.
01 Overview
Norclostebol is 4-chloro-19-nortestosterone, combining the 4-chloro substitution of clostebol with the 19-nor backbone of nandrolone. The acetate ester provides an injectable depot. It has been used in some European human and veterinary tonic products and remains a name that surfaces in anti-doping and contamination contexts (the clostebol family has featured in accidental-exposure cases).
Human pharmacology is thin and dated. Structurally it should be non-aromatising (the 4-chloro group blocks aromatisation, like clostebol) while retaining 19-nor progestogenic character, giving moderate lean-mass anabolism with low estrogenic activity but meaningful suppression.
02 Mechanism
Androgen receptor agonist; the 4-chloro group blocks aromatisation while the 19-nor backbone confers progestogenic activity. The acetate ester is hydrolysed to release the active steroid.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Anecdotal / historical | 50–150 mg/wk | IM | Based on historical tonic dosing and clostebol-family analogy; no modern clinical data. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Lean mass and recovery19-nor anabolism with low water retention; inferred from clostebol/nandrolone class. | Moderate | Preclinical | |
| Low estrogenicity4-chloro substitution prevents aromatisation, limiting estrogenic side effects. | Non-aromatising | Preclinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| HPTA suppression / progestogenic effectsStrong suppression plus 19-nor progestogenic effects such as libido loss. | Severe | Universal | Preclinical | |
| Anti-doping detectability / contamination riskChloro-19-nor metabolites are detectable and the clostebol family has been implicated in contamination-based positive tests. | Mild | Common | Observational |