Increase in formalin-induced tonic pain by 5alpha-reductase and aromatase inhibition in female rats

► Finasteride and letrozole increased formalin-induced tonic pain in female rats. ► Morphine-induced antinociception was inhibited by these inhibitors. ► Inhibitors also increased pain in ovariectomized rats. ► The activity of 5α-reductase and aromatase modulates formalin-induced tonic pain.