Last Modified: July 9, 2014
Tamoxifen works by blocking estrogen receptors in breast tissue. While estrogen may not actually cause breast cancer, it is necessary for the cancer to grow in estrogen receptor-positive breast cancers. With estrogen blocked, the cancer cells that feed off estrogen may not be able to survive.
How to Take Tamoxifen
Tamoxifen comes in pill form to be taken orally (by mouth). The usual dose is 20-40mg per day. Take this medication should be swallowed whole (do not chew or break) with a full glass of water.
Possible Side Effects of Tamoxifen
There are a number of things you can do to manage the side effects of Tamoxifen. Talk to your doctor or nurse about these recommendations. They can help you decide what will work best for you. These are some of the most common side effects:
Nausea and/or Vomiting
If you have nausea or vomiting, notify your doctor or nurse so they can help you manage this side effect. They may prescribe anti-nausea medications. In addition, dietary changes may help. Avoid things that may worsen the symptoms, such as heavy or greasy/fatty, spicy or acidic foods (lemons, tomatoes, oranges). Try antacids, (e.g. milk of magnesia, calcium tablets such as Tums), saltines, or ginger ale to lessen symptoms. Read the Nausea & Vomiting Tip Sheet for more suggestions.
Call your doctor or nurse if you are unable to keep fluids down for more than 12 hours or if you feel lightheaded or dizzy at any time.
There are a few things you can do to help with hot flashes. Several medications have been studied, including clonidine (a blood pressure medication), some low dose antidepressants (such as venlafaxine), and gabapentin. Non-medical recommendations include: keeping well-hydrated with eight glasses of water daily, wearing cotton or lightweight, breathable fabrics, dressing in layers, exercising on a regular basis (generally walking exercise is best), practicing relaxation exercises, and avoiding triggers such as warm rooms, spicy foods, caffeinated beverages, and alcohol.
Some vaginal bleeding can be normal. This may be due to irregular periods that can result from having had chemotherapy. Vaginal bleeding may also be due to the natural change into menopause. However, women who are already post-menopausal at the time they start tamoxifen should report any vaginal bleeding to their oncologist, primary physician or gynecologist. You will need to be checked to determine why you are bleeding. Tamoxifen can stimulate the lining of the uterus to grow, which can result in uterine polyps, and rarely, in uterine cancer.
Uterine (Endometrial) Cancer
In clinical trials, women taking tamoxifen were more likely to have endometrial cancer as compared to women who took placebo. This risk was very small, and doctors believe that the benefits of tamoxifen outweigh this risk. Women should promptly report any menstrual irregularities, vaginal bleeding, pelvic pressure/pain, or any vaginal discharge, as these may be symptoms of endometrial cancer. An endometrial biopsy should be done to test for cancer if any of these symptoms occur.
Women on tamoxifen have an increased risk of getting cataracts. You should get a yearly eye exam by an ophthalmologist. Report any vision changes, cloudy or blurry vision, difficulty with night vision, sensitivity to light, fading or yellowing of colors, as these can be symptoms of cataracts.
Blood clots are a rare side effect that can occur anywhere in the body. They occur most frequently in the calves or the lungs. Women at risk for developing blood clots include those with a family history of blood clots, smokers, those who have an inactive lifestyle, older women, and those with other medical problems. Women with any one of these risk factors may want to consider another therapy that does not have this side effect.
Signs of a blood clot in the leg may include any of the following: leg pain, warmth, swelling of one leg more than the other. Signs of a blood clot in the lung could include: fever, shortness of breath that comes on you very quickly, racing heart, chest pain (that tends to be worse when you take a deep breath).
If you have any of these signs or symptoms of blood clots, you will need to be seen immediately so that you can be treated. Blood thinners can be given. Call your doctor or nurse.
Depression may occur as a result of some of the biological changes occurring in your body and/or your emotional response to some of these changes. Either way, symptoms of depression may include sadness, sleep and appetite changes, as well as a lack of desire to do the activities you once enjoyed. This is very treatable. Please talk to your doctor or nurse if you feel that you are experiencing any of these symptoms.
While on cancer treatment you may need to adjust your schedule to manage fatigue. Plan times to rest during the day and conserve energy for more important activities. Exercise can help combat fatigue; a simple daily walk with a friend can help. Talk to your healthcare team and see OncoLink's section on fatigue for helpful tips on dealing with this side effect.
Vaginal dryness and related painful intercourse is one of the more common side effects of cancer therapy. Vaginal lubricants and moisturizers can help with these concerns. Learn more about specific recommendations for dealing with this side effect. In addition, the desire for sex may decrease during treatment.