[1] Epristeride is a 5α-reductase inhibitor and works by decreasing the production of dihydrotestosterone (DHT), an androgen sex hormone, in certain parts of the body like the prostate gland.

[3][4] Epristeride is a selective, transition-state, non-competitive or uncompetitive, irreversible inhibitor of 5α-reductase,[6][7] and is specific to the type II isoform of the enzyme similarly to finasteride and turosteride but unlike dutasteride.

[8] Epristeride is unique in its mechanism of action relative to finasteride and dutasteride in that it binds irreversibly to 5α-reductase and results in the formation of an unproductive complex of the 5α-reductase enzyme, the substrate testosterone, and the cofactor NADPH.

[8] Moreover, in spite of the fact that epristeride is a very potent inhibitor of 5α-reductase type II (0.18–2 nM), it has been found to reduce circulating levels of dihydrotestosterone (DHT) by only 25 to 54% following 8 days of therapy over a dosage range of 0.4 to 160 mg/day.

[8] For this reason, relative to other 5α-reductase inhibitors like finasteride and dutasteride, the degree of DHT suppression with epristeride falls short of that desirable for full clinical benefit.