desvenlafaxine will boost the level or result of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Warning/Check. Desvenlafaxine inhibits CYP2D6; with greater desvenlafaxine doses (ie, four hundred mg) lessen the CYP2D6 substrate dose by up to fifty%; no dosage adjustment wanted with desvenlafaxine doses seven consecutive times right awa