Fatigue is the most common side effect of breast cancer treatment. Some doctors estimate that 9 out of 10 people experience some fatigue during treatment.

Fatigue is hard to describe. You feel like you don't have any energy and are tired all the time. But there's not a specific cause. You haven't been running errands all day, working out, or doing some other strenuous chore. When you're tired from exertion, if you get enough sleep that night, you usually feel better the next day. With fatigue, you feel generally tired all the time and lose interest in family, friends, and things you normally like to do.

Fatigue is the most common side effect of breast cancer treatment. Some doctors estimate that 9 out of 10 people experience fatigue at some point during treatment. Fatigue from treatment can appear suddenly, at any time, and can be overwhelming. Rest doesn't ease fatigue and it can last for months after treatment ends.

In this section, you can read about how to recognize fatigue, the possible causes of fatigue, and steps you can take to manage fatigue.


How to recognize fatigue

You may think you're simply tired, but if your feelings of listlessness and disinterest go on for weeks, you probably have fatigue. Symptoms of fatigue include:

  • lack of energy

  • sleeping more

  • not wanting to do normal activities or being unable to do them

  • paying less attention to personal appearance

  • feeling tired even after sleeping

  • trouble thinking or concentrating

  • trouble finding words or speaking


Possible causes of fatigue

Several breast cancer treatments can cause fatigue.

Surgery can disrupt your body’s normal rhythm and can often cause fatigue that lasts longer than you may expect. General anesthesia and after-surgery discomfort, pain medication, and restricted activity can also cause fatigue.

Chemotherapy medicines often reduce the number of red blood cells, immune cells, and platelets (clotting cells) your bone marrow produces. Chemotherapy medicines also can damage some cells or limit their ability to function. Low blood cell counts can contribute to fatigue. For example, if you have a low red blood cell (the cells that deliver oxygen from your lungs to your cells) — a condition known as anemia — you'll probably have less energy. If your immune cell count is low, you're less able to fight off infections. Infections and fever can lead to fatigue. Chemotherapy also may cause early menopause, which changes the balance of hormone in your body and can lead to fatigue.

Radiation is often followed by fatigue that can last a few weeks or months. When you're getting radiation, you may be weak from earlier surgery or chemotherapy. The daily demands of radiation therapy change your schedule and make you feel even less energetic and the result can be fatigue. Radiation therapy to a large area of bone can lower your red blood cell and immune cell counts, especially if you're getting chemotherapy at the same time. Low blood cell counts can contribute to fatigue.

Hormonal therapy reduces the effect of estrogen in your body, just like going through menopause, which can make you feel tired and weak. Many pre-menopausal women have menopausal side effects while taking hormonal therapy, such as hot flashes, which can disrupt your sleep and lead to fatigue. Hormonal therapies include:

Targeted therapy medicines, like chemotherapy, can reduce the number of immune cells your bone marrow produces. Low blood cell counts can contribute to fatigue. If your immune cell count is low, you’re less able to fight off infections. Infections and fever can lead to fatigue. Targeted therapy medicines that can cause fatigue are:

Immunotherapy medicines

Many pain medications, such as codeine and morphine, also can cause fatigue. Steroids, which may be part of your treatment plan, can disrupt your ability to get the deep sleep you need to feel well-rested. So even if you get 8 hours of sleep, you may still feel tired. Steroids can also cause weight gain and muscle loss, which can make you feel tired. Once you stop taking these medications, the fatigue eases.

Fatigue can be made worse by other breast cancer treatment side effects such as:

Poor nutrition also may play a role in causing fatigue. Eating less and not getting enough of the nutrients you need because of treatment side effects can cause fatigue. For more information, see Ways to Manage Fatigue.


Fatigue and depression

Depression may be a side effect of breast cancer and fatigue is often a symptom of depression. Some people may have a tendency to depression, which treatment can make worse. At the same time, fatigue itself can lead to depression. Not knowing why you feel drained week after week — and not knowing that this abnormal feeling is normal for many people going through treatment — can make you depressed.

Treatment for breast cancer may leave you feeling sad, tired, or depressed. These feelings are complex conditions, resulting from and affected by many factors: your cancer diagnosis and treatment, aging, hormonal changes, your life experiences, and your genetics.

If you're abruptly going through menopause 10 years earlier than you naturally would, with a quick lowering of hormone levels, you may experience feelings similar to postpartum depression.

Sadness is a natural part of your breast cancer experience, something you need to express and move through. If you don't allow yourself to feel sad and grieve, the unresolved grief gets in the way of feeling better and getting better. You may be having hot flashes and trouble sleeping. You may be feeling overwhelmed or even debilitated. All of these factors can lead to fatigue and depression.

How can you tell the difference between fatigue, sadness, and clinical depression? The symptoms of clinical depression include:

  • an inability to cope

  • an overwhelming feeling of helplessness and hopelessness

  • inertia

  • an inability to concentrate

  • memory problems

  • panic attacks

  • loss of pleasure in what used to make you happy

  • lack of interest in sex or food

  • sleep problems

If you think you're depressed, talk to your doctor. If your doctor doesn't have experience treating depression, ask for the name of an accredited psychotherapist. Together you can sort out if what you're feeling is depression or extreme fatigue. Therapy can help you feel supported and allow you to talk about what's bothering you. Antidepressant medicines can help ease feelings of sadness and anxiety and help you feel better. An accredited psychotherapist with experience treating depression can help.


Ways to manage fatigue

If you think you're experiencing fatigue, talk to your doctor. If possible, give your doctor specific information about your fatigue. Instead of saying, "I'm tired all the time," give an example such as, "I get tired when I walk up the five stairs to my office."

Because there are so many causes of fatigue, there's no one medicine that can relieve fatigue. Together, you and your doctor can figure out ways to reduce or manage your fatigue.

Learn ways to help manage your fatigue.

— Last updated on June 29, 2022, 3:04 PM


Reviewed by 3 medical advisers
Lillian Nail, PhD
Russell Portenoy, MD
Marisa C. Weiss, MD
Lankenau Medical Center, Wynnewood, PA
Learn more about our advisory board
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