A Pilot Study of Varying Doses of Tamoxifen in the Setting of Genetic Polymorphisms of CYP2D6

Inclusion Criteria: * Women taking tamoxifen 20mg a day * Tamoxifen use for \> 90 days. * Use an accepted barrier form of contraception. Exclusion Criteria: * Patients are excluded if they are pregnant or lactating; if pre- menopausal, the patient will have a documented negative pregnancy test and use an accepted barrier form of contraception. * Patients are excluded if they have a medical history of Hepatitis B. Hepatitis C or HIV * Patients are excluded if they use Tobacco * Patients are excluded if they have a medical history of hereditary hemochromatosis * Patients are excluded if they have elevated AST (SGOT), ALT (SGPT), Bilirubin or Alkaline Phosphate o Defined as greater than 2 1/2 times the upper limit of normal * Patients are excluded if they are being treated with chemotherapy * Patients are excluded if they are taking any of the following oral medications, as they are potent CYP2D6 inhibitors: * Fluoxetine (Prozac) * Miconazole (Monistat) * Paroxetine (Paxil) * Quinidine * Ritonavir (Norvir) * Atorvastatin (Lipitor) * Carvedilol (Coreg) * Clarithromycin (Biaxin) * Dipyridamole (Persantine) * Erythromycin * Grapefruit Juice * Itraconazole (Sporanox) * Ketoconazole * Mefloquine * Nelfinavir (Viracept) * Nicardipine (Cardene) * Nilotinib * Propranolol (Inderal) * Ranolazine (Ranexa) * Saquinavir ( Invirase) * Verapamil Covera-HS * Warfarin (Coumadin) * Chlorpromazine (Thorazine) * Cinacalcet (Sensipar) * Delavi…