Symptoms and side effects in someone with cancer and dementia

About symptoms and side effects

A person with cancer and dementia may have symptoms or side effects caused by cancer or cancer treatment. These can usually be prevented or well-controlled.

Symptoms or side effects will depend on the type of cancer or treatment. We have more information about the most common side effects.

The person you care for may not be able to tell you if they have symptoms or side effects. You may have to ask them regularly. If they have problems communicating, it can help to look for signs in their body language or facial expressions.

Some symptoms or side effects of cancer may be like the ones caused by dementia. If the person you care for has symptoms you are worried about, talk to the doctor or nurse.

Memory or concentration problems

Some people having treatment for cancer may have:

  • memory problems
  • difficulty concentrating
  • feelings of extreme tiredness.

This is called ‘chemo brain’. Despite its name, it can happen to people having other types of cancer treatment.

People with dementia are more likely to have this side effect. Some of these problems are like the ones caused by dementia. For some people having treatment, dementia symptoms may get worse temporarily. For others, this change may be permanent.

The doctor or nurse can give you more information and support before you and the person you care for decide if they will have treatment.

Poor appetite and eating problems

If the person you care for has symptoms of cancer or side effects from treatment, they may find it hard to eat. Problems that can affect eating include:

If dementia is already affecting a person's appetite, this may be worse.

Some people may struggle to eat enough. Others may eat more than usual, which can lead to weight gain.

Talking to a dietitian

If you think the person you care for is not eating well, ask their GP or specialist nurse to refer them to a dietitian. Dietitians can give advice about any changes you can help them make.

If the person is struggling to eat and losing weight, the dietitian may give them food supplements.

Healthy eating tips

Eating a balanced diet and keeping to a healthy weight may help stop problems such as constipation and dehydration. These problems can make confusion worse for people with dementia.

Here are some healthy eating tips to help someone with cancer and dementia:

  • Make sure the person you care for does not overeat.
  • Encourage them to eat less saturated fat and sugar, such as cakes, crisps and sweets.
  • Make sure they eat plenty of fruit, vegetables and high-fibre foods. This will help prevent constipation.
  • Encourage them to drink plenty of fluids during the day. About 2 litres (3½ pints) can help prevent constipation and stop them from becoming dehydrated.
  • If they find it hard to use cutlery, try foods they can pick up with their fingers.
  • Help them look after their teeth with regular dental checks. If they have dentures, make sure they fit properly.

We have more information about:

We also have recipes for people affected by cancer, which you might find helpful.

Dementia UK has a leaflet on helping someone with dementia look after their teeth and mouth.


Some people with cancer and dementia are more likely to become constipated. It is important for someone with dementia to avoid constipation. This is because it can make them more confused.

The main reason people with cancer and dementia get constipated is not drinking enough. They may also get constipated because:

  • they are not eating enough
  • they cannot move around enough
  • they are taking painkillers that cause constipation.

Try to encourage the person you care for to drink more fluids and eat more fruit and high-fibre foods. If constipation is a problem, tell their GP, district nurse or specialist nurse. They may recommend laxatives, suppositories or enemas.

It can help to keep a note of the person’s bowel movements. This may help you prevent or treat constipation before it becomes severe or makes them more confused.


People often worry that cancer causes severe pain. But not everyone will have pain, even if the cancer is advanced. If the person you care for is in pain, it can usually be controlled with painkillers.

Some people with dementia may not be able to tell their carers they are in pain. Look for signs of pain in the behaviour of the person you care for. For example, they may:

  • become agitated or tearful
  • start shouting out
  • hold the part of their body that is sore
  • change their facial expression or clench their teeth
  • become pale or sweaty
  • refuse help or care
  • become withdrawn.

Doctors and nurses can use a tool to assess if these behaviours are caused by pain or something else. The tool is a checklist of types of behaviour. It looks at how mild or severe the behaviour is. This can help hospital doctors or GPs decide whether to give someone painkillers.


Painkillers are usually tablets, capsules or liquids taken by mouth (orally). The person you care for may have problems swallowing medicines or remembering to take them. If this happens, they can be given painkiller patches that stick to the skin.

You can do some simple things to help with pain and discomfort in the person you care for. You could try:

  • changing their position
  • using heat pads, hot water bottles or ice packs
  • asking if they would like a massage.

You could also offer them over-the-counter or prescribed painkillers regularly. You should only give these exactly as instructed on the packet.

Sometimes the person you care for may need specialist help to assess their pain and symptoms. The doctors and nurses can adjust the dose of medicines or add new ones to control symptoms. Some people may have a short stay in the hospice to do this. Once their symptoms are controlled, they may be able to go home again.

We have more information about pain and ways to manage it.

Sleep problems

Having both cancer and dementia may cause problems sleeping at night. Getting a good night’s sleep can stop someone with dementia from feeling tired during the day. Feeling very tired during the day can make symptoms of dementia worse.

There are different reasons why someone may not be sleeping well. It can help to look for changes in sleep patterns. If there are changes, try to find out if something is causing them. There may be things you can do to help.

Increasing physical activity

Keeping physically active during the day may help the person sleep at night. If they can do some gentle exercise, you could try doing it with them. For example, you could go on short walks together.

Managing physical problems

If physical problems such as pain, discomfort or feeling unwell are stopping them from sleeping, talk to their GP, district nurse or specialist nurse. They may be able to give the person medicines that help with the symptoms of cancer or side effects of cancer treatment. You may also be able to get equipment that may make them more comfortable, such as a pressure-relieving mattress.

Managing emotional problems

Some people find that anxiety, worry and emotional distress are keeping them awake at night. To support the person you care for, you could let them know that you are there to listen or talk things through with them.

We have helpful information about starting conversations and listening. We also have information about sleep problems and advice on how to get a good night’s sleep.

‘Sundowning’ is when a person’s dementia symptoms get worse in the evening, around dusk. Dementia UK has more information explaining sundowning and how to cope with the effects.

Using a symptom diary

You may find it useful to note down symptoms in a symptom diary. You can write down any symptoms and what helps. It might be useful to show the diary to a doctor or nurse so they can help.

About our information

  • References

    Below is a sample of the sources used in our bowel cancer information. If you would like more information about the sources we use, please contact us at

    Alzheimer’s Society. Dementia 2015: Aiming higher to transform lives. 2015.

    Gosney et al. Dementia and Cancer: A review of current literature and practices. 2013.

    The Dementia Engagement and Empowerment Project (DEEP) Guide: Writing dementia-friendly information. 2013.

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 01 November 2020
Next review: 01 November 2023

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.