desvenlafaxine will improve the degree or effect of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Caution/Check. Desvenlafaxine inhibits CYP2D6; with better desvenlafaxine doses (ie, four hundred mg) reduce the CYP2D6 substrate dose by nearly fifty%; no dosage adjustment needed with desvenlafaxine doses 7 consecutive days promptly pr