Some breast cancer patients taking tamoxifen may not be getting the full benefit of their treatment because they have also been taking selective serotonin reuptake inhibitors, prescribed drugs that inhibit the effect of an important enzyme, CYP2D6. In a new study, scientists have shown that by taking action as soon as interacting medications are found, patients can be weaned off and switched to a different treatment with no deleterious effect on tamoxifen metabolism.