What are cognitive changes (chemo brain)?

Cognitive changes include problems with memory, concentration and how a person can think. 

These problems were first reported after chemotherapy treatment. For example, researchers first looked at this in women with breast cancer. They 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 these problems could be due to various reasons. This includes the different cancer treatments and the cancer itself. Doctors might refer to these problems as:

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

Cognition means the mental processes that take place in the brain. It includes:

  • thinking
  • attention
  • language
  • learning
  • memory
  • perception (to see, hear, or become aware of something through your senses)

Signs and symptoms

Most people who have cognitive changes can 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 or image for a particular object
  • difficulty remembering 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
  • being unusually disorganised
  • having difficulty learning new skills

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 uncertain how many people with cancer have mild cognitive impairment. Studies looking at this have reported a wide range of different figures. It is thought that up to 75 out of every 100 people (75%) experience cognitive changes during treatment. Up to 35 in every 100 people (35%) have symptoms after treatment.

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 exactly clear what causes these cognitive changes in people with cancer. Researchers think that treatments may cause changes and inflammation in brain cells. They suggest 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 treatments such as surgery, chemotherapy, hormone therapy, radiotherapy, immunotherapy 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

Some people might be more likely to have cognitive impairment following a cancer diagnosis and treatment. Risk factors include:

  • older age
  • lifestyle
  • genetics
  • anxiety, depression, post traumatic stress disorder (PTSD), fatigue, and difficulty staying and falling asleep (insomnia) related to a cancer diagnosis and treatment

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 several 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. They may continue for years after treatment has finished.


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

  • Long-Term Cognitive Dysfunction in Cancer Survivors

    Z Országhová and others

    Frontiers in Molecular Biosciences, 2021 December. Volume 14, Issue 8, Page: 770413

  • Prevalence of cognitive impairment and change in patients with breast cancer: A systematic review of longitudinal studies

    A Dijkshoorn and others

    Psychooncology, 2021 May. Volume 30, Issue 5, Pages: 635 to 648

  • 'A new normal with chemobrain': Experiences of the impact of chemotherapy-related cognitive deficits in long-term breast cancer survivors

    F Henderson and others

    Health Psychology Open, 2019 March 5. Volume 6 Issue 1, Page: 2055102919832234

  • Cancer-related cognitive impairment: current perspectives on the management of cognitive changes following cancer treatment

    G Binarelli and others

    Expert Review of Neurotherapeutics, 2023 March. Volume 23, Issue 3, Pages: 249 to 268

  • 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: 
26 Jun 2023
Next review due: 
26 Jun 2026

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