What are cognitive changes (chemo brain)?

Cognitive changes mean changes in memory, concentration and the way a person is able to think.

These problems were first reported after chemotherapy treatment. For example, researchers first looked at this in women with breast cancer and found that chemotherapy might be the cause. So these changes used to be called chemo brain. Another name people use is chemo fog.

But the term chemo brain is misleading. Doctors now think that these problems could be due to a variety of reasons, including the different cancer treatments and the cancer itself. Doctors might refer to these problems as:

  • cancer related cognitive impairment
  • cancer associated cognitive decline
  • mild cognitive impairment
  • cognitive dysfunction   

Cognition basically means thinking. In psychology, it means the way you process and recall information. And the way you understand the world and how it works.

Signs and symptoms

Most people who have cognitive changes are able to do everyday things. But they may notice they aren’t able to do some things quite as well as before they had cancer. Symptoms can include:

  • memory loss – forgetting things that you normally remember
  • difficulty thinking of the right word for a particular object
  • difficulty following the flow of a conversation
  • trouble concentrating or focusing on one thing
  • difficulty doing more than one thing at a time (multi tasking)
  • more difficulty doing things you used to do easily, such as adding up in your head
  • fatigue (tiredness and lack of energy)
  • confusion
  • mental fogginess

The changes are often mild and very subtle. But if you have them they can reduce your quality of life.

Who gets cognitive changes (chemo brain)?

It’s not certain how many people with cancer have mild cognitive impairment. Studies looking at this have reported a wide range of different figures. It can range from 15 out of every 100 people (15%) to 90 in every 100 people (90%).

It can affect people with different types of cancer and at different times. For example, people might notice changes:

  • at diagnosis (before treatment starts)
  • during treatment
  • after treatment

It can affect men and women of all ages.

What causes it?

It’s not clear what causes these cognitive changes in people with cancer. But research suggests that it could be a combination of factors including:

  • the diagnosis of cancer and all the stress and emotion that this brings
  • the cancer itself
  • cancer treatment such as chemotherapy, hormone therapy, radiotherapy and some targeted drugs
  • very intensive treatment such as high dose chemotherapy followed by a stem cell transplant
  • side effects of treatment such as fatigue, low levels of red blood cells in the blood (anaemia), sleep disturbances or hormonal changes
  • low mood, stress and anxiety

People might be more likely to have cognitive impairment following a cancer diagnosis and treatment if they:

  • are older
  • already have problems with memory and thinking or anxiety and depression

How cognitive changes might affect you

The symptoms of cognitive impairment can come and go. How much you notice them seems to depend on what you're doing. For example, if you need to juggle a number of things as part of your normal day, you might notice it more than someone who doesn’t. People often notice it more when they go back to work. Tiredness usually makes the symptoms worse.

For most people, the symptoms have either gone or improved a lot within a year of ending treatment. But for some people the symptoms can be long term and may continue for years after treatment has finished.

Research suggests that people who have mild cognitive impairment are also more likely to have depression, anxiety, and fatigue. We don’t know whether mild cognitive impairment leads to these problems. Or whether having depression, anxiety or fatigue makes you more likely to develop cognitive impairment.


There are things you can do to help you cope and improve your symptoms.

  • Cancer-related cognitive impairment: an update on state of the art, detection, and management strategies in cancer survivors

    M. Lange and others

    Annals of oncology, December 2019. Vol 30, Issue 12, p1925-1940

  • Cognitive Effects of Cancer and Cancer Treatments
    TA Ahles and JC Root
    Annual Review of Clinical Psychology, 5 January 2018. Volume 13, issue 7, pages 1-27

  • Emerging pharmacotherapy for cancer patients with cognitive dysfunction

    J Davis and others

    BMC Neurology 2013, Vol 33 (153)

  • What is known and unknown about chemotherapy-related cognitive impairment in patients with haematological malignancies and areas of needed research

    A M Williams and others

    British Journal of Heamatology 2016, Vol 174 (6), p.835-846

  • Cognition and Cognitive Impairment in Older Adults with Cancer

    A Magnuson and others

    Current Geriatrics Reports 2016, Vol 5, (3), p. 213–219

  • Prevalence of perceived cognitive dysfunction in survivors of a wide range of cancers: results from the 2010 LIVESTRONG survey

    J E Schmidt and others

    Journal of Cancer Survivorship 2016, Vol 10 (2), p.302-311

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. Please contact patientinformation@cancer.org.uk with details of the particular issue you are interested in if you need additional references for this information.

Last reviewed: 
25 Aug 2020
Next review due: 
25 Aug 2023

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