desvenlafaxine will raise the amount or effect of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Monitor. Desvenlafaxine inhibits CYP2D6; with higher desvenlafaxine doses (ie, four hundred mg) lower the CYP2D6 substrate dose by approximately fifty%; no dosage adjustment required with desvenlafaxine doses 7 consecutive times stra