What Is Cancer Fatigue and What Causes It?

Why Am I So Tired? Symptoms and Causes of Cancer Fatigue

Mature woman sleeping in bed
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Cancer fatigue is one of the most common and annoying symptoms you may experience during lung cancer treatment. In one study, cancer survivors quoted fatigue as interfering with their quality of life more than nausea, depression, and pain combined. In addition to lowering quality of life, fatigue may be a risk factor in lowering survival. 

We all talk about being tired, but the fatigue associated with cancer treatment is much different. What does cancer fatigue feel like, what causes it, and what can you do to feel better?

Signs and Symptoms

Cancer fatigue is different from ordinary tiredness—the kind of tiredness you experience after a busy day, or when you haven’t had enough sleep. With cancer fatigue, you can feel tired despite an excellent night’s rest, and determination (or caffeine) just doesn’t work to get past it. You may experience any of these symptoms as you live with fatigue during cancer treatment:

  • An overwhelming sense of tiredness often described as “whole body” tiredness
  • Tiredness that persists despite rest
  • Becoming tired even with simple activities, such as walking to the mailbox
  • Difficulty concentrating
  • Feeling more emotional than you ordinarily would
  • Rapid onset of fatigue
  • Less desire to participate in activities you usually enjoy

Everyone experiences the fatigue of cancer treatment in different ways, but most people agree that it is a different sense of tiredness than they experienced prior to cancer treatment.


There are many causes of fatigue. Some of these are related to the cancer itself, some due to treatment, and others related to the day-to-day stress of living with lung cancer. Some of these are treatable; whereas others can be managed by recognizing your limitations at this time and making needed adjustments. Recent research suggests that inflammation may play a key and underlying role in cancer fatigue.

Some causes of fatigue during cancer treatment include:

  • The cancer itself. Changes in your metabolism due to the cancer itself can drain your energy
  • Treatment and side effects of treatment. Chemotherapy, radiation therapy, and surgery can all contribute to tiredness
  • Shortness of breath. The increased work of breathing when you feel short of breath can sap your energy
  • Depression. Depression and fatigue often go hand-in-hand, and it can be hard to determine which symptoms came first
  • Anemia. Anemia, due to bleeding following surgery, chemotherapy, or simply being ill, can lower your energy level
  • A low oxygen level in your blood (hypoxia). Oxygen-poor blood can make you feel more tired
  • Medications. Several medications used during cancer treatment, including pain medications, can contribute to fatigue
  • Uncontrolled pain. Pain clearly increases fatigue, so it is important to discuss any uncontrolled pain you have with your oncologist
  • Lack of rest, or resting too much. Both a lack of, and an excess amount of rest, can increase fatigue
  • Immobility and lack of activity. Deconditioning, from time spent in the hospital or recovering at home, can lower your energy level
  • Stress. Stress can make you feel more tired, and the stress of being limited by fatigue increases this further
  • Difficulty eating. This is often due to loss of appetite, mouth sores, or taste changes. Inadequate nutrition can lower your reserve and add to your sense of tiredness


The most important thing you can do for yourself is to recognize that cancer fatigue is real and unique. Share your symptoms with your oncologist at each visit. He or she will want to rule out any treatable causes such as anemia.


If it is your loved one coping with cancer fatigue and not yourself, please know that this symptom is very real. In fact, many people with cancer feel frustrated that their loved ones don't understand. In addition to fatigue, check out what people living with lung cancer have shared in this article on "what it really feels like to live with cancer."

When to Talk to a Doctor

You should share any symptoms you are experiencing with your oncologist—including fatigue—at each appointment. He or she may have suggestions for coping, or consider changes in your treatment plan. Clinical studies are in progress looking at both medications (such as Ritalin) and cognitive behavioral counseling ("talk therapy") as methods of treating cancer fatigue. Make sure to contact your health care team between visits if you note any sudden changes in your energy level, if your tiredness is interfering with daily activities such as eating, or if you find that coping with the fatigue of cancer has become overwhelming in any way.

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