desvenlafaxine will improve the degree or influence of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Keep an eye on. Desvenlafaxine inhibits CYP2D6; with greater desvenlafaxine doses (ie, 400 mg) lessen the CYP2D6 substrate dose by nearly fifty%; no dosage adjustment desired with desvenlafaxine doses 7 consecutive times immedia