Tamoxifen Side Effects & Benefits: What you Need to Know
tamoxifen side effects
Marian Barnick

Marian Barnick

Registered Kinesiologist and Human Movement Specialist


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Tamoxifen Side Effects & Benefits

In my blog post last week I talked about tamoxifen which is being prescribed for certain types of breast cancers.  

Because it’s become a mainstream therapy AND because it’s surrounded with some controversy, I thought we should dive a little deeper on the topic of tamoxifen including tamoxifen side effects and benefits.  It’s always important to make the best decision for you and your specific needs. 

With this knowledge, you’ll be able to make an informed decision and have a great conversation with your Oncologist if this is one of the treatments offered to you.


Targeted Therapy

Targeted therapy is one type of treatment that is used to reduce the risk of cancer recurrence.

Targeted therapy is a type of cancer treatment that works on specific cells that cancer needs to grow and spread.  Drugs have been developed that target these specific cells.  When these specific cells aren’t available or can’t bind with the cancer cells, the cancer cells aren’t able to grow and therefore can’t spread.


In order to see what type of cells are within your tumor, a biopsy is done.  Your Oncologist will review the biopsy results and can then determine if there is a targeted therapy that works on your specific type of tumor.


A biopsy is the same procedure that’s used to determine if breast cancer tumors are hormone receptor positive or hormone receptor negative.  Hormone receptor positive breast cancer are tumors that have estrogen or progesterone receptors (or both).  This type of breast cancer accounts for 70% to 75% of all invasive breast cancer cases.


There is a special type of targeted therapy that works on receptor positive breast cancers.  Because the identified target in this type of breast cancer is a hormone, the targeted therapy that’s used is called Hormone Therapy.


Hormone Therapy

Hormone therapy for breast cancer works by either lowering the estrogen in your body or blocking the estrogen from attaching to the cancer cells.  Either way, the goal is the same which is to limit the hormone that’s required by the cancer cells to grow.


Hormone therapy may also be prescribed if cancer cells have returned or spread to other parts of the body as well as to decrease the risk of recurrence.


Hormone therapy is generally used with other forms of treatment such as surgery and chemotherapy but as I outlined last week, it can be prescribed on its own.  The specific hormone therapy we’re discussing is tamoxifen and its target is estrogen.


As I mentioned, up to 75% of invasive breast cancer is hormone positive so tamoxifen is prescribed to a large number of breast cancer patients.  Tamoxifen can be prescribed to patients who have any stage of breast cancer and the goals of treatment can be different depending on the stage.


The usual prescription is one pill, daily, for five years.  However, sometimes hormone therapies can lose their effectiveness as cancer cells become resistant to them.  Therefore, other types of treatment may need to be prescribed.

Recent studies show that there are increased benefits with patients taking tamoxifen for 10 years.


There’s been great data to show decreases in recurrence for women using tamoxifen as an adjuvant therapy – after their main type of treatment is completed.


Tamoxifen can also be prescribed as neo-adjuvant therapy – before surgery with the goal of shrinking the tumor.  With a smaller tumor, surgery can be less invasive and reduce the amount of tissue that is taken from the breast.

Tamoxifen can be prescribed to women who are premenopausal or postmenopausal.


If you are postmenopausal and taking menopause hormone therapy (MHT) you will probably be asked to stop this treatment.

Tamoxifen has been prescribed to women who are at high risk of developing breast cancer as a treatment to prevent breast cancer.


Some anti-depressant medications can interfere with tamoxifen treatment.

Tamoxifen Benefits

Tamoxifen is prescribed because it has been proven to reduce the risk of cancer recurrence.

The National Cancer Institute funded a large study in 1998.  The results showed a 50 percent reduction in both invasive and non-invasive breast cancer in women treated with tamoxifen.

Tamoxifen has been shown to shrink tumors before surgery to allow for less invasive surgeries.

Tamoxifen has been shown to improve survival rates for hormone receptor positive breast cancer patients.


Tamoxifen Side Effects

The controversy always comes when you weight the tamoxifen side effects against the benefits.  Although tamoxifen works by decreasing the availability of estrogen to breast tissue, tamoxifen can act just like estrogen to other cells in the body and this can increase some risk factors.


As with any drug, some side effects are more common and some are rare.  The big picture is to know as much as you can so you can make an informed choice that’s right for you.


It’s important to note that some studies have shown that the length of treatment, age of the patient, and whether she is premenopausal or postmenopausal have an affect on the types of side effects.


Tamoxifen Side effects can include:

  • hot flashes
  • fatigue
  • vaginal dryness
  • mood swings
  • nausea
  • headache
  • constipation
  • leg swelling

The risk is low but there is an increased risk for endometrial cancer, deep vein thrombosis (DVT), and stroke.  If cancer has spread to the bones, there can be pain and swelling in joints and muscles called tumor flares.  Tamoxifen may affect fertility and patients are advised to avoid pregnancy while taking tamoxifen.


Of particular concern to premenopausal women is the risk of bone loss or osteopenia (which can lead to osteoporosis).  Therefore, your doctor may order a bone density test as well as blood work before starting tamoxifen and during treatment for a comparison.  If there is bone loss while on treatment, there are other medications that may be prescribed to help boost your bone density like bisphosphonates.


Interesting to note is that tamoxifen can work in just the opposite way in postmenopausal women and help to strengthen bones.  Postmenopausal women prescribed aromatase inhibitors instead of or after tamoxifen can have an increased risk of bone loss.


Tamoxifen and Exercise

Whether you’re premenopausal or postmenopausal, whether you take Tamoxifen or not, your Oncologist will recommend that you exercise.

It’s important for your to know what specific types of exercise are best for you physically as well as for the goals you’ve set for yourself.


You may decide that the tamoxifen side effects are important to review prior to making your choice of the types of exercise you want to include in your program.



If you’ve got shoulder range of motion deficits because of surgery / treatment, you need to make sure you’ve incorporated movement therapy and a great stretching program PRIOR to taking on any strength training.

Check out this post Where to Start with Breast Cancer Rehab After Surgery (click the title) for more information on the foundational shoulder movements and  where you need to start after breast cancer surgery.


Weight bearing exercise is important for tamoxifen side effects that can lead to bone loss and once your range of motion improves, strength training will also be an important consideration.

The most important part to any exercise program is to ensure you’re moving well.  Because of the compensations that occur after surgery and because of breast cancer treatment side effects including issues with balance, muscle loss, and tightness, breast cancer survivors find ways to continue to function with day-to-day activities that put extra stress on their musculoskeletal system and increase the risk of injuries and pain symptoms.

Aside from the benefits to bone health that exercise provides,  exercise will also help with fatigue which can be a tamoxifen side effect as well as a long term side effect from chemotherapy.  And of course, exercise provides benefits to your mood and mental health as well.

So…..do you see what I’m doing here?  Giving you a not so gentle push to get your butt  moving.

If you need support in deciding what exercises are best for you, start with my YouTube channel  Monday Moves with Marian. These corrective strategies are focused on the specific exercise needs for breast cancer survivors who want to exercise safely and get back to a more active life.

National Cancer Institute
ACSM Guide to Exercise and Cancer Survivorship

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