Testosterone Buciclate
An ultra-long-acting testosterone ester (trans-4-n-butylcyclohexane carboxylate) developed as a candidate depot for hormonal male contraception and hypogonadism, with a single injection sustaining levels for many weeks. Its effects are those of testosterone; it was studied in small human trials but never widely marketed.
01 Overview
Testosterone buciclate (also written 20-Aet-1) is a very lipophilic ester designed to prolong release far beyond enanthate or cypionate. In WHO- and NIH-supported contraceptive research, single 600-1200 mg intramuscular doses raised testosterone for six to twelve weeks or more, making it one of the longest-acting injectable testosterones ever tested in humans.
Despite promising kinetics it was never commercialised, partly because achieving reliably supraphysiologic contraceptive levels required large, sometimes impractical doses. Effect and side-effect profiles mirror testosterone once the ester is hydrolysed; the ester's distinctive feature is its extremely slow, flat release. Human data exist but are limited to small trials, hence a moderate research score.
02 Mechanism
The bulky cyclohexane-carboxylate ester is hydrolysed very slowly in the depot, releasing free testosterone over weeks. The liberated hormone acts through the androgen receptor and undergoes normal aromatisation and 5-alpha reduction.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Hypogonadism (trial) | 600 mg | IM | Single depot every ~12 weeks in clinical studies. |
| Contraceptive research | 1000–1200 mg | IM | Single higher dose for suppressive contraceptive levels; infrequent injections. |
Ester comparison
| Ester | Half-life | Injection freq. | Testosterone by mass |
|---|
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Sustained testosterone levelsSingle injection maintains levels far longer than conventional esters. | 6-12+ weeks per injection | Clinical | |
| Increased lean massFrom the parent hormone acting on the androgen receptor. | Clinical | ||
| Spermatogenesis suppression (contraceptive intent)In contraceptive trials, sustained levels suppressed sperm output; desirable in that context, an adverse effect otherwise. | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| HPTA suppressionProlonged suppression of gonadotropins and spermatogenesis; recovery is slow given the long ester. | Severe | Universal | Clinical | |
| Estrogenic effectsWater retention and gynecomastia risk from aromatisation. | Moderate | Dose-dependent | Clinical | |
| ErythrocytosisRaised haematocrit with sustained supraphysiologic exposure. | Moderate | Dose-dependent | Clinical |