desvenlafaxine will enhance the amount or influence of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Warning/Watch. Desvenlafaxine inhibits CYP2D6; with higher desvenlafaxine doses (ie, 400 mg) lower the CYP2D6 substrate dose by as many as 50%; no dosage adjustment essential with desvenlafaxine doses seven consecutive days quickly be… Read More