Drugs to avoid for women taking tamoxifen

By Blossom Paravattil and Megan Cole
Updated 2010

For most breast cancer tumors, the female hormone estrogen makes tumor cells grow and multiply. The drug tamoxifen was developed to block estrogen and therefore treat, prevent, and stop the reoccurrence of those types of breast cancer. These types of breast cancers are known as “estrogen receptor-positive breast cancers,” which means that the cancers are sensitive to estrogen.

For taxmoxifen to do its job blocking estrogen, it needs to be broken down in the body by a key enzyme known as CYP2D6.¬† The enzyme may not be able to break down the tamoxifen if a woman is taking other medicines that interfere with CYP2D6, and therefore reduce tamoxifen’s effectiveness.

Medical experts recommend that women who are taking tamoxifen avoid taking medications that interfere with the enzyme. The table below shows a list of drugs that may decrease the effectiveness of tamoxifen and provides alternative drugs that can be taken instead.

Classes of drugs Drugs that are likely to interfere with tamoxifen Alternative drugs that should be safe to take with tamoxifen
Antidepressants(SSRI/SNRIs) Paxil, Prozac, Wellbutrin, and Cymbalta Effexor, Pristiq, Edronax, Lexapro, and Remeron
Antipsychotics Mellaril, Trilafon, and Orap Navane, Clozaril, Zyprexa, Geodon, and Seroquel
Cardiac Drugs Cardioquin and Ticlid Cardizem
Medications for Infectious Diseases Seldane and Cardioquin Crixivan, Invirase, Viracept, Rescriptor, Viramune, and Sustiva
Miscellaneous Medication Sensipar * Neurontin

*Cinacalcet is used to treat high parathyroid hormone levels, which are often a result of end-stage renal disease. It may also be used for the treatment of hypocalcaemia in patients with parathyroid carcinoma.

Antihistamines, which are taken to prevent or treat allergies and allergy symptoms such as watery eyes and a runny nose, may cause problems with tamoxifen as well. To avoid these problems, use antihistamines such as chlorepheniramine (Triaminic Allergy, Chlor-trimeton), cetrizine (Zyrtec), and loratadine (Claritin, Alavert). Additionally, cimeidine (Tagamet) should be avoided, whereas rantidine (Zantac) is ok to use.

So if you are taking tamoxifen, be sure to avoid any medications that interfere with its effectiveness.


Dezentje, VO et al. Effect of Concomitant CYP2D6 Inhibitor Use and Tamoxifen Adherence on Breast Cancer Recurrence in

Early-Stage Breast Cancer. J Clin Oncol. 2010: 28:2423-2429.

Sideras, K et al. Coprescription of Tamoxifen and Medications That Inhibit CYP2D6. J Clin Oncol. 2010: 28:2768-2776

The American Society of Health-System Pharmacists, Inc. (2008 Sept. 1) Cinacalet. Retrieved from <http://www.nlm.nih.gov/medlineplus/druginfo/meds/a605004.html>