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Managing Cancer Care

What is Fatigue or Weakness?

Fatigue and weakness are often used to describe the same thing. But they actually are different.


Weakness is a feeling of decreased strength and needing extra effort to move a certain part of the body or the entire body. Weakness is due to loss of muscle strength. Weakness can be a big part of why cancer patients feel fatigue.


Fatigue is feeling extremely tired or lacking energy, often described as being exhausted. Fatigue is something that lasts even when a person seems to be getting enough sleep. It can have many causes, including working too much, having disturbed sleep, stress and worry, not having enough physical activity, or going through an illness and its treatment.

The fatigue that often comes with cancer is called cancer-related fatigue. It's very common. Between 80% and 100% of people with cancer report having fatigue. The fatigue felt by people with cancer is different from the fatigue of daily life and different from the tired feeling people might remember having before they had cancer.

People with cancer might describe it as feeling very weak, listless, drained, or “washed out” that may decrease for a while but then comes back. Some may feel too tired to eat, walk to the bathroom, or even use the TV remote. It can be hard to think or move. Rest might help for a short time but does not make it go away, and just a little activity can be exhausting. For some people with cancer, this kind of fatigue causes more distress than pain, nausea, vomiting, or depression.

What causes fatigue and weakness ?

    In people with cancer, weakness might be caused by having and recovering from surgery, low blood counts or low electrolyte (blood chemistry) levels, infection, or changes in hormone levels.

    However, the causes of cancer-related fatigue are often harder to determine because there are often many factors involved. It might be from the cancer itself and/or a side effect of the cancer treatment. How cancer and treatment might cause fatigue is not well understood, but some possible reasons are:

    • Cancer and cancer treatment can change normal protein and hormone levels that are linked to inflammatory processes which can cause or worsen fatigue.
    • Treatments kill normal cells and cancer cells, which leads to a build-up of cell waste. Your body uses extra energy to clean up and repair damaged tissue.
    • Cancer forms toxic substances in the body that change the way normal cells work.

    Besides direct effects of cancer and its treatment, people with cancer often also experience other things that can add together to increase fatigue. These are things like surgery, stress and worry, changes in activity level, and changes in blood counts, electrolytes, and hormone levels.

    How long does fatigue or weakness last?

    Fatigue caused by cancer and its treatment can last for weeks, months, or years. It often lasts after treatment ends.

    • For people who have surgery for cancer with no other treatment, fatigue often decreases or goes away over time as they recover from surgery.
    • For people getting chemotherapy, targeted therapy, or immunotherapy in cycles, fatigue often gets worse at first and then may get better until the next treatment, when the pattern starts again.
    • For those getting radiation therapy, fatigue usually gets worse as the treatment goes on and often lessens within a few months after treatment is complete.

    Fatigue can:

    • Differ from one day to the next in how bad it is and how much it bothers you
    • Be overwhelming and make it hard for you to feel well
    • Make it hard for you to be with your friends and family
    • Make it hard for you to do things you normally do, including going to work
    • Make it harder for you to follow your cancer treatment plan.

    What to look for

    • You feel tired and it doesn’t get better with rest or sleep, it keeps coming back, or it becomes severe.
    • You’re more tired than usual during or after an activity.
    • You’re feeling tired and it’s not related to an activity.
    • You’re too tired to do the things you normally do.
    • Your arms and legs feel heavy and hard to move.
    • You have no energy.
    • You feel very weak.
    • You spend more time in bed and/or sleep more. Or, you may have trouble sleeping.
    • You stay in bed for more than 24 hours.
    • You become confused or can’t concentrate or focus your thoughts.
    • Your tiredness disrupts your work, social life, or daily routine.

    It may be hard for you to talk about it, but tell your cancer care team about your fatigue. Tell them how it’s affecting your life. Someone on your team should be able to help you if they know you’re having this problem. Managing fatigue is part of good cancer care. Work with your cancer care team to find and treat the causes of your fatigue.


    The American Cancer Society medical and editorial content team

    Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.

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    Last Revised: February 1, 2020

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