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Cancer itself can cause fatigue directly by spreading to the bone marrow, causing anemia (uh-nee-me-uh, a low red blood cell count). Or it can cause fatigue indirectly, by forming toxic substances in the body that change the way normal cells work.

Fatigue is also a common side effect of many cancer treatments, like chemotherapy, radiation, stem cell transplant, and immunotherapy. Cancer treatments often kill fast-growing healthy cells, especially the cells in the bone marrow that make blood. This causes fatigue because red blood cells carry oxygen to fuel all the cells in the body. Too few red blood cells (anemia) means too little energy to meet the body’s needs. Treatments kill normal cells and cancer cells, which leads to a build-up of cell waste. The body needs extra energy to clean up this waste and repair damaged tissue.

Doctors don’t always know exactly what’s causing a person’s fatigue. Talking with your doctor about it is the first step in trying to find out its cause. Even when the doctor knows what’s causing it, there’s often no “quick fix.” But there are things that you and your doctor can do that might make it better.

Here are some questions about fatigue and your cancer treatment that you may want to ask:

  • Will my cancer treatment cause fatigue?
  • Is my fatigue caused by anemia? If so, how will it be treated?
  • How bad is the fatigue likely to get?
  • What can be done to control my fatigue or make it better?
  • If my fatigue gets bad, how will you treat it?
  • What can be done if the fatigue doesn’t get better with treatment?
  • What are the likely side effects of the treatments for fatigue?
  • Are there other health care professionals who can help manage my fatigue?

Other things that can affect fatigue

Fatigue is different for every cancer patient. Many treatment-related and disease-related factors have been linked to fatigue, but doctors still don’t know exactly what causes cancer-related fatigue.

You should be checked for other things that often worsen fatigue, too, Managing them can greatly help reduce the fatigue. Some are:

  • Anemia
  • Pain
  • Emotional distress (including depression and anxiety)
  • Sleep problems
  • Medicines you are taking
  • Other medical problems (such as infection; low thyroid function or other gland problems; or heart, lung, liver, kidney, or nervous system disease)
  • Nutrition problems
  • Low level of physical activity
  • Use of alcohol and other non-prescribed drugs


A low red blood cell count is called anemia. Your red blood cell count will be measured with a blood test called a CBC. (CBC stands for complete blood count.) Doctors often define anemia as a blood hemoglobin (Hb) level of less than 12 g/dL (grams per deciliter). But many people do not feel much different until the hemoglobin level falls below 11 g/dL. Symptoms of anemia get worse as the hemoglobin gets lower. These symptoms can include:

  • Fast heart beat
  • Shortness of breath
  • Trouble breathing on exertion (such as when walking or climbing stairs)
  • Dizziness
  • Pale skin, mouth, or nail beds
  • Fatigue

There are many different causes of anemia. Your health care team will try to find out what’s causing yours, so they can treat it and help you feel better.

For more information on anemia, please see our document called Anemia in People With Cancer.


Cancer pain can make you less active, make you not want to eat, cause sleep problems, and cause depression – all of which can lead to fatigue. Cancer pain should not be accepted as part of cancer treatment. Something can always be done to make pain better.

Talk to your doctor or nurse to get more information about treating cancer pain. You can also learn more in our document, Guide to Controlling Cancer Pain.

Emotional distress

People diagnosed with cancer go through a lot of unpleasant emotions. There are many different types of feelings, from anger to depression, but their overall effect is distress. Distress can include a feeling of sadness about the loss of good health or fear of what will happen in the future. It’s normal to have these feelings. But sometimes the distress becomes so great that it causes physical problems like fatigue. Depression and anxiety are common types of distress that can cause or worsen fatigue.

For more information on distress, see our documents called Distress in People With Cancer and Anxiety, Fear, and Depression.

Sleep problems

If you wake up often during the night, have trouble falling asleep, or wake up early in the morning and cannot go back to sleep, you are probably not getting the rest you need. This change in your sleep can lead to fatigue. Tell your doctor or nurse about your sleep problems. They will try to find out why you are having trouble sleeping so they can help plan the best treatment for this problem.


Many medicines can cause fatigue and problems with thinking. This includes certain over-the-counter drugs, and possibly other supplements, as well as prescription medicines. The drugs most likely to cause fatigue are

  • Pain medicines
  • Sleep medicines
  • Anti-depressants
  • Anti-nausea medicines
  • Anti-seizure medicines
  • Certain antihistamines
  • Certain heart medicines

Some of these drugs can also make you feel sleepy. The degree of sleepiness varies from person to person. Taking many drugs with many side effects may make fatigue worse, too. It’s important to tell your health care team about all vitamins, herbs, supplements, and medicines you are taking. Don’t forget the non-prescription drugs and those you use every now and then as needed.

Keeping a journal of everything you take, along with the doses, times, and when you have symptoms, might help you find out which ones may be part of your fatigue.

Other medical problems

Many people have other medical problems or illnesses that are not related to cancer but may add to fatigue. These illnesses should be identified and treated. Examples of other medical problems that may be part of fatigue are:

  • Heart problems, such as congestive heart failure (CHF)
  • Lung problems, such as emphysema or shortness of breath
  • Kidney problems, such as kidney failure
  • Brain problems, such as seizures or dementia
  • Infections, such as pneumonia, urinary tract infections, or viral illnesses
  • Dehydration
  • Low adrenal gland function (rare, but can cause low blood pressure, fainting, and dehydration)
  • Low sex hormones (such as estrogen in women or testosterone in men)
  • Low thyroid function

If needed, your doctor can test you to find out if any of these are making your fatigue worse. For example, low thyroid gland function is fairly common in people in the United States. It can often be detected by a simple blood test and is easy to treat. Your doctor may be able to find and treat problems such as these to help with your fatigue.

Poor nutrition

The body needs protein, carbohydrates, fats, vitamins, minerals, and water to do its work. In people with cancer, changes in nutrition can affect fatigue. These changes include how well the body can process nutrients and the need for more energy than usual. It can also have to do with poor intake of food, fluids, and certain minerals. The changes can be caused by:

  • Changes in metabolism (the body’s ability to break down and use food)
  • The need to repair damaged cells
  • Uncontrolled tumor growth competing for nutrients (the cancer takes energy, protein, vitamins, and the like, for its own growth)
  • Poor appetite (you don’t feel like eating)
  • Nausea and vomiting
  • Diarrhea

You may have blood tests to measure things like sodium, potassium, calcium, and magnesium. Your body needs these important minerals. You can ask to be referred to a registered dietitian who can help you learn how to best meet your nutrition needs during this time.

You can find more information on nutrition in our document called Nutrition for the Person With Cancer During Treatment: A Guide for Patients and Families.

Lack of exercise

Cancer treatment along with less physical activity can make you less able to do the things you used to do. And you might find that it takes much more effort and more energy to do the things you need to do. This can make fatigue worse. Physical exercise can help you build up your stamina to do more of your usual activities and have less fatigue.

Talk to your doctor before you start any exercises. A careful work-up by a physical therapist can help you plan the right exercise program for you. You can find more information in our document called Nutrition and Physical Activity During and After Cancer Treatment: Answers to Common Questions.

Alcohol or other non-prescribed drugs

Alcohol and other “recreational” drugs might make you feel better for a short time, but in the long run make you feel more tired and disrupt your sleep. They can also interact with the cancer drugs you are taking, and may cause their own medical problems. If you think drinking or other drugs might be a problem for you, talk honestly with your doctor about how much and how often you drink or use drugs. You may need a special program to manage your intake safely.

Last Medical Review: 12/10/2012
Last Revised: 12/10/2012