Finasteride, a 5alpha-Reductase Inhibitor, Potentiates Antinociceptive Effects of Morphine, Prevents the Development of Morphine Tolerance and Attenuates Abstinence Behavior in the Rat

The study investigated the effects of finasteride, a 5α-reductase inhibitor, on morphine's analgesic properties, tolerance, and dependence in rats. It was found that finasteride enhanced the antinociceptive effects of morphine and effectively blocked the development of tolerance and dependence when administered chronically. Although a single dose of finasteride did not reverse established tolerance, it did prevent withdrawal symptoms precipitated by naloxone. These findings suggested a functional relationship between the 5α-reductase enzyme and morphine, indicating that finasteride could potentially modulate morphine's effects in the central nervous system.