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Causes of fatigue

A number of things can cause fatigue in people with cancer. This includes the cancer itself and the type of treatment you might have.

Who could have fatigue

We don't fully understand what causes cancer fatigue, but we know that a number of things can contribute to it. Fatigue is often worse in people who:

  • are having a combination of treatments
  • have an advanced cancer
  • are elderly

It is important that you know you are more likely to suffer from fatigue if you fall into one of these groups. Report any signs to your doctor so that they can manage your fatigue properly.

What could cause fatigue

Fatigue can be one of the first symptoms of cancer. It could be because there is cancer in the bone marrow and that slows down the production of red blood cells, causing anaemia.

A cancer that affects your hormone levels could cause fatigue.

People with advanced cancers seem more likely to have fatigue than people in the earlier stages. This could be because there are more cancer cells in the body.

Tumours produce substances called cytokines such as tumour necrosis factor, that cause tiredness. Some cancers also produce toxic substances that stop cells making chemicals in the body, such as potassium or calcium. These chemicals are important for keeping your muscles and heart working. You might feel sleepy and fatigued if their levels are low.

Cancer in your lungs can cause breathlessness and this can make you feel fatigued. Also if you have a fluid build up in your abdomen (ascites), you could have fatigue. 

You could have other medical conditions that cause fatigue such as:

  • heart problems
  • diabetes
  • being overweight
  • problems with your lungs
  • depression

Your cancer and the treatment you are having may make your fatigue worse. Many people become depressed at some time after a diagnosis of cancer.

Depression is an illness. It is as physical a problem as any other illness and needs treatment. People with depression often feel as if they have no energy at all. They have to drag themselves out of bed in the morning. Even though they are exhausted people with depression often wake early in the morning and cannot get back to sleep.

Tell your doctor or nurse if you think you may be depressed. It is possible to have short courses of anti depressants and they could really help you to feel more able to cope.

Fatigue is a common side effect of many cancer treatments. Even though you might not be able to stop your treatment, knowing it's the cause of your fatigue can help you to cope better. The side effects of cancer treatments can also make fatigue worse. Feeling sick, having trouble sleeping or generally feeling low can make you feel like you have less energy. The following treatments can cause fatigue. 


You are likely to feel some fatigue after surgery for your cancer. This may last for a few weeks or months after your operation. People often underestimate how long it takes to get over surgery. Surgery stresses your body and it needs time to heal. You may have felt quite anxious before your operation, and the feeling of letting go and relaxing afterwards can leave you very tired. It is a bit like the build up to an important event in your life which leaves you feeling exhausted for some time afterwards. Pain can be exhausting. And the anaesthetic and other drugs may also contribute.


Most people who have radiotherapy feel increasingly tired as they go through their treatment. Travelling back and forth to the hospital for treatment can make you feel very tired. But there also seems to be a direct effect from the radiation itself. Fatigue can last for several weeks and for some people it can last for months after treatment has finished. 

You might develop an extreme form of tiredness called somnolence syndrome if you have had radiotherapy to your brain.


Nearly everyone who has chemotherapy has some fatigue. Your white and red blood cell counts drop midway between treatments. Many people feel very tired at this time. After that, you get a bit of energy back. Then it's time for your next treatment and so it goes on. Knowing that you will get tired again can make you feel anxious and frustrated.

Biological therapy

Biological therapy is a type of cancer treatment. These drugs can cause tiredness. They can affect how the body produces chemicals that it needs in order to work properly.

Hormone treatment

Many hormone treatments can disturb the body’s balance and the speed it does things. This is called your metabolism. Changing your metabolism can lead to several side effects including fatigue.

Drugs that block hormones are used to treat some cancers for example breast cancer or prostate cancer. This can cause fatigue as a side effect. It is similar to the fatigue that women going through menopause have. Thyroid hormones used to replace hormones after surgery for thyroid cancer sometimes cause weakness and difficulty sleeping. Sometimes this can lead to fatigue.

Other drugs can also make you feel drowsy or tired these include:

  • painkillers
  • anti sickness drugs
  • anti depressants
  • cough medicines
  • sleeping tablets
  • steroids

Fatigue can be worse if you are taking a combination of these drugs. Talk to your doctor if you think your tablets and medicines are making you unnecessarily tired. But don’t stop taking anything until you’ve spoken to your doctor or specialist nurse.

Cancer and its treatment can affect your bone marrow. The bone marrow is where your body makes red blood cells which carry oxygen around your body.

A lower than normal red blood cell count is called anaemia. Having too few red blood cells means your blood carries less oxygen and you can have:

  • shortness of breath
  • tiredness and lack of energy
  • dizziness
  • loss of appetite
  • difficulty concentrating
  • an increase in heart rate
  • chest pain
  • depression

Let your doctor know if you have any of these symptoms. A blood test can easily check your red cell count and show if you are anaemic. You can have treatment for anaemia.

Some cancer treatments can affect your appetite. The treatment can make you feel sick and not want to eat much. But you could start to feel tired and weak if you are eating fewer calories than your body needs. This is very common in people with cancer.

Diarrhoea and vomiting are other side effects of treatment that can cause fatigue.

Your cancer may affect the way your body processes food (your metabolism). This can stop your body from using your food to give you energy or put on weight. So you lose weight even if you are eating normally. This can lead to a condition called cachexia that some people with advanced cancer have.

Cachexia causes muscle wasting. You lose weight and can't cope with much exercise. Even walking to the corner shop can make you very tired.

Cancer can sometimes cause pain. Dealing with pain can make you feel very tired. So controlling pain can help to reduce fatigue.

Being diagnosed with cancer can be hard to accept and you are likely to go through a range of emotions before, during and after your treatment. This is very normal.

You might have a lot of worries.

  • Will my treatment work?
  • Will I be able to deal with side effects?
  • How will my family and friends cope?
  • Will I have enough support?
  • Will I be able to keep working?
  • How will I get to the hospital for my treatment?
  • Will the treatment be painful?
  • What if I lose my hair?

All these worries can make you feel anxious or down. Anxiety and depression are common in people with cancer and they are very draining emotions.

You may find it useful to look in coping emotionally with cancer for information on how to cope with some of these worries.

What else can cause fatigue

A number of other factors can make you feel tired and fatigued if you have cancer. Not sleeping well at night or sleeping too much during the day can add to your fatigue.

Treatment may be harder for you to cope with and make you feel more tired especially if you are elderly. Your tiredness may make it harder for you to concentrate so everything seems more difficult which can make you feel even more tired.

Travelling to and from the hospital for treatment can be very tiring.

Having a lot of visitors when you are staying in hospital can make you feel very tired too.

You can ask your nurses to tell your visitors that they can only stay with you for a short time. Don't feel bad if you have to do this. You need a lot of rest and your friends and family will understand.

Last reviewed: 
04 May 2016
  • Cancer Principles & Practice of Oncology (10th edition)

    V T DeVita and others

    Wolters Kluwer 2015

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