Breast cancer can make a person feel tired and fatigued. This can occur as a symptom of the cancer itself, or as a side effect of cancer treatments, such as hormone therapy, chemotherapy, and radiation therapy.

Fatigue occurs commonly with cancer, including breast cancer. According to the American Cancer Society, between 80–100% of people with cancer develop fatigue.

Cancer fatigue includes feeling weak, tired, or low in energy. Severe cancer fatigue can interfere with everyday activities and reduce a person’s quality of life. Fortunately, there are steps a person can take to reduce cancer fatigue.

This article provides an overview of the factors that can cause breast cancer fatigue and provides tips for managing fatigue. We also offer advice on when to speak with a doctor about fatigue.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Breast cancer fatigue can occur as a symptom of breast cancer or as a side effect of its treatment.

A 2019 study followed 332 women referred for a mammogram and compared levels of fatigue among women who received a cancer diagnosis compared with those who did not. Fatigue was greater for women who received a breast cancer diagnosis and was most severe during the first 6 months following the diagnosis.

Breast cancer fatigue can occur as a result of multiple factors, including:

  • the disease itself
  • the psychological impact of receiving a cancer diagnosis
  • side effects due to cancer treatments

Below are some possible causes of breast cancer fatigue.

Doctors may prescribe hormone therapy to treat breast cancer or to decrease the risk of its recurrence.

The hormone estrogen feeds some types of breast cancer. Suppressing estrogen may reduce the risk of such breast cancers recurring. Treatment may include hormonal therapies, such as:

However, changes in hormone levels may lead to some of the same symptoms as menopause. According to the American Cancer Society (ACS), hormones used to treat breast cancer can cause various side effects, including:

Learn more about hormone therapy for breast cancer here.

Fatigue is among the most common side effects of chemotherapy.

According to The National Cancer Institute (NCI), the cause of fatigue during cancer treatment is not always clear and may involve more than one factor.

For example, chemotherapy may decrease red blood cell and then white blood cell levels, which may cause fatigue. Chemotherapy can also trigger nausea and vomiting, which may cause dehydration and associated fatigue.

According to the ACS, chemotherapy and other cancer treatments can also cause fatigue in the following ways:

  • by altering levels of hormones and proteins that contribute to inflammation
  • by creating toxic substances inside the body, which change the way cells function
  • by triggering an accumulation of dead cells, which the body must work hard to remove
  • by damaging tissues, which the body must work hard to repair

Learn more about the link between chemotherapy and fatigue here.

People who undergo radiation therapy for breast cancer may also experience fatigue due to certain physiological changes occurring within the irradiated cells.

According to a 2021 meta-analysis, the severity of radiation-induced fatigue depends on the following:

  • the type of radiation therapy
  • the dose of radiation
  • the amount of tissue that receives radiation
  • whether the person is receiving additional cancer treatments.

In addition, radiation therapy often includes treatment 5 days a week. The demands of daily treatment can contribute to tiredness and fatigue.

Surgery for breast cancer may also cause fatigue, especially in the first few weeks following the procedure.

The anesthesia from surgery may leave a person feeling tired for several days. According to, surgery also affects the body’s natural rhythm, causing low energy. Some people may also experience post-surgical pain or discomfort, which can contribute to fatigue.

The type and extent of surgery may play a role in the level of fatigue a person experiences.

Although everyone handles a cancer diagnosis differently, it is not uncommon for a person to experience emotions such as anxiety and depression. These emotions can sap a person’s energy. They may also lead to poor sleep, which contributes to tiredness and fatigue.

One 2020 review of research stated that female breast cancer survivors reporting fatigue also often reported experiencing depression, insomnia, and cognitive dysfunction alongside.

Learn more about coping with a cancer diagnosis here.

There are various methods a person can try to help manage cancer-related fatigue. Some examples are outlined below.

Talk with a cancer specialist

A person should talk with a cancer doctor to determine the possible causes of fatigue. The doctor may make recommend the following to help combat fatigue:

  • changing existing medications or medication dosages
  • nutritional counseling
  • mental health support


People might expect that physical activity would worsen feelings of fatigue. However, research suggests that exercise may help reduce fatigue both during and after cancer treatment.

A 2017 meta-analysis compared different interventions for combatting cancer-related fatigue. The results indicated that exercise and physiological interventions were more effective at decreasing fatigue compared to medication.

Before starting an exercise program, a person should talk with their doctor to determine the best exercise program for their condition.

Stay well-hydrated

Dehydration may cause fatigue. A person who is undergoing chemotherapy or radiation therapy may experience nausea, vomiting, and diarrhea, all of which can cause dehydration.

A person who is undergoing cancer treatment should try to drink plenty of fluids to avoid dehydration.

Consider complementary treatments

According to the NCI, complementary medicine may help to reduce fatigue associated with cancer treatment.

There is very little research into the effects of complementary treatments on breast cancer fatigue. Some options that people may wish to try include:

Balance rest with activity

Resting too much can make the body weaker. However, overdoing activity can also cause fatigue.

A person should aim to achieve a healthy balance between rest and activity. This may involve periods of gentle exercise followed by short breaks or naps throughout the day, as needed.

Seek support

One way to conserve energy is to accept help with everyday chores and responsibilities. A person can try asking family members and friends for help with tasks that need completing, such as cleaning or shopping.

Support may also include professional counseling. According to the ACS, behavioral therapy and mindfulness-based stress reduction can help decrease cancer-related fatigue in some people.

Although some level of fatigue is common with breast cancer, it is helpful to discuss this symptom with a doctor.

A doctor may need to conduct further investigations to establish the exact cause of breast cancer fatigue and work up an appropriate treatment plan. The sooner a person speaks with their doctor, the sooner they can begin treatment to help improve their energy levels.

A person should consider talking with a doctor if they experience any of the following symptoms:

Breast cancer and its treatment can lead to increased fatigue.

The outlook for people with breast cancer-related fatigue may vary according to the type of breast cancer and its symptoms, as well as the type and duration of cancer treatment. Individual factors may also play a role, such as a person’s age, overall health, and response to treatment.

In many cases, energy levels improve a few months after completing cancer treatment. However, it may take several months for fatigue to completely resolve.

Fortunately, treatments and lifestyle changes may help to reduce fatigue and improve energy levels. A person can talk with their doctor or oncology team for further tips and advice on how to combat cancer fatigue.