desvenlafaxine will increase the degree or result of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Caution/Keep an eye on. Desvenlafaxine inhibits CYP2D6; with larger desvenlafaxine doses (ie, four hundred mg) minimize the CYP2D6 substrate dose by as many as 50%; no dosage adjustment necessary with desvenlafaxine doses 7 consecutive