desvenlafaxine will raise the amount or impact of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Caution/Watch. Desvenlafaxine inhibits CYP2D6; with greater desvenlafaxine doses (ie, 400 mg) lessen the CYP2D6 substrate dose by as much as fifty%; no dosage adjustment needed with desvenlafaxine doses 7 consecutive days quickly ahead of