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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.
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:
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.
Fatigue caused by cancer and its treatment can last for weeks, months, or years. It often lasts after treatment ends.
Fatigue can:
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 journalists, editors, and translators with extensive experience in medical writing.
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National Comprehensive Cancer Network. (NCCN). Cancer-related fatigue. Version 1.2019. Accessed at www.nccn.org/professionals/physician_gls/f_guidelines.asp on September 18, 2019.
Oncology Nursing Society (ONS). Symptom interventions: Fatigue. Accessed at https://www.ons.org/pep/fatigue on January 2, 2020.
Qu D, Zhang Z, Yu X, et al. Psychotropic drugs for the management of cancer-related fatigue: a systematic review and meta-analysis. Eur J Cancer Care (Engl). 2015 Oct 21. doi: 10.1111/ecc.12397. [Epub ahead of print]
Last Revised: February 1, 2020
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