Background: Benign Prostatic Hyperplasia (BPH), and Prostate Cancer (PCa) are androgen-dependent diseases. PCa is associated with excessive signalling of the androgen receptor (AR) due to the binding of 5α-DHT and T. BPH is related to high levels of 5α-dihydrotestosterone (5α-DHT), biosynthesized from testosterone (T) by 5α-reductase (5RD5A). The inhibition of 5RD5A and the blockage of AR are targets for their treatment. In this study, the synthesis and determination of biological activity of the new N-cyclohexyl-3β-hydroxyandrosta-5,16-diene-17-carboxamide (6), N-cyclohexyl-3-oxoandrosta-4,6,16-triene-17-carboxamide (7), and N-cyclohexyl-3-oxoandrosta-4,16-diene-17-carboxamide (8) were carried out to find new drugs to improve these afflictions. Methods: The synthesis of 6 to 8 was confirmed by spectroscopic and spectrometric analyses. Competitive binding assays determined the affinity of 6 to 8 to the AR. The inhibitory activity of 5RD5A isoform 2 (5RD5A2) (IC50) was established by the conversion of [3H]-T to [3H]-5α-DHT and it was compared with finasteride (FIN). The pharmacological effect of 6 to 8 was determined on the weight of the prostate and seminal vesicles glands of castrated hamsters treated with T, and on the diameter size of their flank organs. Results: Compounds 7 and 8 bound lightly (ca. 15 %) to AR. Comparing to FIN (IC50 = 8.5 nM), 6 to 8 (IC50 = 0.169, 0.105 and 0.155 nM, respectively) showed higher potency as inhibitors of 5RD5A2. Compound 6 decreased the prostate and seminal vesicles weight, as well as the hamsters' diameter flank organs. However, 7 only decreased the diameter of flank organs. Surprisingly, 8 increased these pharmacological parameters. Conclusion: Androstane-17-caboxamide 6 is a 5RD5A2 inhibitor that reduces the weight of androgen-dependent glands such as the prostate, suggesting it could be a lead for new drugs to treat BPH and PCa.