Causes of fatigue | Cancer Research UK
Cancer Research UK on Google+ Cancer Research UK on Facebook Cancer Research UK on Twitter

Causes of fatigue

Landing page coping image

This page tells you about the possible causes of cancer fatigue. There is information on


Who may 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.


The cancer itself

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. If their levels are low, you may feel sleepy and fatigued.

We have more about research into how cancers cause fatigue.


Other health problems

You may 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. Often, even though they are exhausted, they wake early in the morning and cannot get back to sleep. If you think you may be depressed, tell your doctor or nurse. It is possible to have short courses of anti depressants and they could really help you to feel more able to cope.


Side effects of treatment

Fatigue is a common side effect of many cancer treatments including

Even though you may not be able to stop your treatment, just knowing it is the cause of your fatigue may help you to cope better. As well as the treatments causing fatigue, their side effects can make fatigue worse. If you feel sick, have trouble sleeping or generally feel low, you will have less energy.


If you have surgery for your cancer you are likely to feel some fatigue. 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 may last for months after treatment has finished. 


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 uses substances made by the body to treat cancer. These drugs can cause tiredness. They may affect how the body produces chemicals that it needs 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.

Side effects of other drugs

Drugs that can make you feel drowsy and tired include


Painkillers can make you feel tired when you start taking them, but this usually passes after a few days as your body gets used to them.

Anti-sickness drugs

Some anti-sickness drugs may make you feel sleepy and tired. Let your doctor know if this happens, as you may be able to try other types of anti-sickness drug that suit you better.

Anti depressants

Some anti-depressant medicines can make you feel tired but this may only last for a few days. If you carry on feeling tired let your doctor know. They may be able to prescribe a different anti depressant for you.

Cough medicines

Some cough medicines contain drugs that make you feel very tired. Let your doctor know if this happens so they can help you to find ways of managing the tiredness.

Sleeping tablets

Some sleeping tablets can make you feel a bit fuzzy in the head and slow to start the next morning, but they are not all like that. If you have not been able to sleep for nights on end, a short course of sleeping tablets can break the pattern of not sleeping well. But they don’t allow as much deep sleep as you normally have. So your sleep won’t be as restorative or refreshing as natural sleep. Tablets are best used for a couple of weeks at a time to try to break a pattern of poor sleep. Talk to your doctor if you are worried about this.

We have more detailed information about how to help you get to sleep.


Steroids are often used in cancer care. They are a part of some chemotherapy treatments. Cancer specialists often prescribe steroids to give you a boost if you have fatigue or loss of appetite. But steroids can interfere with your sleep patterns. Some people find it very difficult to get to sleep when they are taking steroids. If possible, try taking them in the morning instead of later in the day. They can also cause muscle wasting, which in turn will make you feel weaker.

Remember - check with your doctor before making any changes to the dose of steroids you take. It can be dangerous to change the dose or stop taking them without a doctor’s advice.

If you are taking a combination of these drugs, your fatigue may be worse. 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 treatment can affect your bone marrow, which is why it often causes fatigue. The bone marrow is where your body makes red blood cells.

Some cancers can also affect your bone marrow, giving you a lower than normal red blood cell count (anaemia). Red blood cells carry oxygen around your body. If you have too few red blood cells, your blood carries less oxygen, and you may have

  • Shortness of breath
  • Tiredness and lack of energy
  • Dizziness
  • Loss of appetite
  • Difficulty concentrating
  • An increase in heart rate
  • Chest pain
  • Depression

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


Problems with eating

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

Side effects of treatment can use up a lot of energy and make all this worse. Sickness and diarrhoea can be exhausting. There is more information about how chemotherapy can affect your digestive system and tips on how to cope in our section about the general side effects of chemotherapy. There is more information about sickness and weight loss from radiotherapy in the section on general side effects of radiotherapy section.



Between 3 and 5 out of 10 people (30 to 50%) being treated for cancer will have some sort of pain. At least 7 out of 10 people (70%) with advanced cancer (cancer that has spread or come back) will have pain of some sort. Dealing with pain can make you feel very tired. So controlling pain can help to reduce fatigue. We have a whole section about cancer pain which you may find helpful.


How you feel emotionally

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 may have a lot of worries such as

  • 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.


Other factors

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. If you are elderly, treatment may be harder for you to cope with and make you feel more tired. Your tiredness may make it harder for you to concentrate, so everything seems more difficult. And that may make you feel even more tired.

Travelling to and from the hospital for treatment can be very tiring. Or if you are staying in hospital, having a lot of visitors 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.

Rate this page:
Submit rating


Rated 5 out of 5 based on 39 votes
Rate this page
Rate this page for no comments box
Please enter feedback to continue submitting
Send feedback
Question about cancer? Contact our information nurse team

No Error

Updated: 4 March 2014