Tamoxifen

How tamoxifen works

Tamoxifen works by blocking estrogen from reaching estrogen receptors on breast cancer cells. Without the estrogen, the cancer cells can’t grow as well as they can with it.

Who gets tamoxifen

Tamoxifen is standard treatment for premenopausal and perimenopausal women with hormone receptor-positive breast cancer. In postmenopausal women, tamoxifen may be used alone or before an aromatase inhibitor.

In early-stage breast cancer, no matter what your menopausal status, tamoxifen used after other treatment reduces the risk of cancer coming back. The benefit happens during the therapy and continues afterward for many years. Studies show breast cancer deaths to be down 30 percent in women 15 years beyond the start of tamoxifen treatment.

How tamoxifen is given

Tamoxifen is taken daily as a pill or in liquid form as tamoxifen citrate (Soltamox). Because your body produces estrogen every day, it’s important to take tamoxifen every day.

In the past, it was standard to take tamoxifen for 5 years, but recent research shows that taking tamoxifen for a total of 10 years further lowers the chance of the cancer returning. How long you take tamoxifen depends on your menopausal status:

• Premenopausal: 5 to 10 years of tamoxifen only
• Perimenopausal: 5 to 10 years of tamoxifen only, if after 5 years of treatment you remain perimenopausal; or 5 years of tamoxifen followed by 5 years of an aromatase inhibitor if you start menopause
• Postmenopausal: up to 5 years of tamoxifen, followed by 5 years of an aromatase inhibitor

Note that aromatase inhibitors are the standard of care for postmenopausal women. If you are postmenopausal and take an AI without taking tamoxifen before, the standard of care remains 5 years of AI therapy.

Side effects and things to remember

Some antidepressants can affect the way your body breaks down tamoxifen. Research shows that bupropion (Wellbutrin), duloxetine (Cymbalta), fluoxetine (Prozac), paroxetine (Paxil), and sertraline (Zoloft) may stop tamoxifen from working as well as it could. It’s also possible that common arthritis medicines (Celebrex), antacids (Tagamet, Zantac), and antihistamines (Atarax, Benadryl) could interact poorly with tamoxifen.

It is not known whether these medicines make tamoxifen less effective. To keep tamoxifen working as well as possible, tell your doctor about all medicines and supplements you take. It’s likely there are good options that won’t affect your tamoxifen treatment.

Like all medicines, tamoxifen has side effects. The issues may be few or none, cause some problems, or truly disrupt your life. Common side effects include:

• hot flashes
• fatigue
• vaginal dryness or discharge
• mood swings
• nausea
• hair thinning
• dry skin
• loss of interest in sex

Serious side effects are rare, but tamoxifen may cause:

• blood clots that could lead to stroke, heart attack or lung blockage
• increased risk of uterine (endometrial) cancer
• liver problems

Tamoxifen also can lower cholesterol and lessen menopause-related bone loss if you are postmenopausal. If you are premenopausal, tamoxifen can cause bone loss.

Talk with your doctor if you had a heart attack or blood clots before. Call your doctor immediately if you have chest pain, abnormal vaginal bleeding, dizziness, leg swelling, severe headache or other symptoms.

Because tamoxifen can harm a fetus, use safe birth control while taking it if you are premenopausal or still have a period every now and then. Discuss this important issue and any side effects you feel with your healthcare team so they can help you.

Your doctor, pharmacist or nurse can help you manage your side effects. You can also go to our section on Side Effects for more information.