Tamoxifen Drug Interactions

by on April 24, 2012

There are several Tamoxifen drug interactions that people taking this medication should be on the lookout for. The best way to prevent any interaction, whether it is mild or severe, is for patients to disclose any over-the-counter or prescription medications they are taking with their physicians and their pharmacists.

Minor and Moderate Drug Interactions

There are a few mild and moderate drug interactions associated with Tamoxifen, though most of these are linked to taking products that contain estrogen or other synthetic hormones. This is because Tamoxifen is designed to block the natural hormones already being produced within the body in an effort to slow the growth of certain types of cancers. Patients should also avoid consuming soybeans and alcohol during their course of treatment with this medication.

Significant Tamoxifen Drug Interactions

Since the purpose of Tamoxifen is to block the production of certain hormones in the body, the lack of these hormones may cause the active ingredients of other medications to become too concentrated, or not concentrated enough, within the bloodstream. Patients should always check the labels of any over-the-counter and prescription medicines they take for the ingredients listed below:

Sleep Aids and Allergy Medications containing Diphenhydramine

There are many medications available over-the-counter and by prescription that contain the active ingredient diphenhydramine. This is an antihistamine that is used to treat the symptoms of allergies, hay fever and hives, and it is sometimes even used to control the symptoms of the common cold. It may cause problems for people who are taking Tamoxifen due to the increased incidence of drowsiness and dizziness. Some of the medications containing diphenhydramine that may interact with Tamoxifen include:

  • Benadryl and Benadryl Products
  • Unisom
  • 40 Winks
  • Calm-Aid
  • Generic allergy medications—check the label for diphenhydramine


There are certain antidepressants that are thought to interact with Tamoxifen. This is because the Tamoxifen itself suppresses hormones within the body that can have a significant impact on the mood. When combined with selective serotonin reuptake inhibitors—commonly known as SSRIs—this impact can turn to severe depression.

Also, these antidepressants may inhibit some of the active enzymes within the drug. Some of the medications that patients should avoid include:

  • Paxil
  • Zoloft
  • Prozac
  • Effexor
  • Cymbalta
  • Citalopram (Celexa)
  • Lexapro

Antipsychotic Medications

Some newer antipsychotic medications contain the active ingredient clozapine, which is used to treat patients who do not respond to typical therapies. These medications can prolong the QT interval of the electrocardiogram, essentially meaning that the patient’s heart does not beat normally. Since Tamoxifen may also have this effect on certain patients, it is generally advised that the clozapine should not be used. Some of the drugs that contain clozapine include:

  • Zaponex
  • Clopine
  • Denzapine
  • FazaClo

Certain Narcotic Pain Relievers

There are certain narcotic pain medications that may cause Tamoxifen to not work as expected.  This is because the enzymes formed during the breakdown process of the pain reliever will reduce or even completely eliminate the effectiveness of Tamoxifen. Individuals who used these pain relievers—all of which contain the active ingredient propoxyphene—were twice as likely to see a recurrence or worsening of their cancer symptoms. Medications that contain this ingredient are:

  • Darvon
  • Darvocet
  • Dolene

Though not all of the possible Tamoxifen drug interactions are listed here, these are the most commonly reported and those that are of the greatest concern. Patients who are taking Tamoxifen should consult their pharmacists and physicians before taking any other prescription or over-the-counter drug.