Managing symptoms and side effects of cancer and dementia

The person you care for may have symptoms or side effects from cancer or its treatment. These can usually be well controlled.

If they are not able to tell you how they feel look for signs in their body language, behaviour or facial expressions.

Some cancer treatments cause memory problems and extreme tiredness. This can seem like dementia is getting worse. Although people with dementia are likely to have this side effect, it should improve with time.

Other symptoms and side effects include:

  • eating problems and constipation - eating plenty of fruit and vegetables and drinking plenty of fluids can prevent these.
  • pain – the persons GP may prescribe painkillers, if they can’t swallow tablets they might be able to have a patch that sticks to the skin.
  • difficulty sleeping – try some gentle exercise together to help improve sleep. If they can’t sleep because of worries let them know you are happy to help talk things through.

Speak to their GP or nurse, they will be able to prescribe medicines to improve most side effects.

Managing symptoms and side effects

The person you care for may have symptoms or side effects caused by cancer or its treatment. Symptoms and side effects can usually be prevented or well controlled.

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. It can help to look for signs in their body language or facial expressions.

Some symptoms or side effects of cancer may be similar to ones caused by dementia. If the person you care for has symptoms that 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 similar to ones caused by dementia and you may worry that the dementia is getting worse. But the symptoms of chemo brain are usually temporary and should improve with time. 

The doctor or nurse can give you more information and support. 

Poor appetite and eating problems

If the person you care for has symptoms or side effects from cancer treatment, they may find it hard to eat. Problems such as having a sore mouth, difficulty swallowing, diarrhoea, constipation or feeling sick can affect how well they eat. If dementia is already affecting their appetite, this may be worse.

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

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 they are struggling to eat and are losing weight, the dietitian may give them food supplements.

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

Here are some healthy eating tips for people with cancer and dementia:

  • They should try not to overeat.
  • They should eat less saturated fat and sugar.
  • They should eat plenty of fruit, vegetables and high-fibre foods. This will help keep their bowels regular.
  • You could encourage them to drink about 2 litres (3.5 pints) of fluids a day. This will help keep their bowels regular. It will also stop them from becoming dehydrated.
  • If they find it hard to use cutlery, try foods that they can pick up with their fingers.
  • Help them look after their teeth with regular dental checks and make sure dentures fit properly.

We have more information about eating problems and cancer, preventing weight loss, and healthy eating. 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, as it can make them more confused.

The main reason people with cancer and dementia get constipated is not drinking enough. Some people get constipated because they aren’t eating enough. Others get constipated because they can’t move around much. Painkillers can also 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 the 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. That way you can prevent or treat constipation before it becomes severe or affects their confusion.


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

Some people with dementia may not be able to tell their carers that they are in pain. Look for signs of pain in their behaviour, such as:

  • becoming agitated, tearful or shouting out
  • holding the part of their body that is sore
  • changes in facial expression or clenching teeth
  • being pale or sweaty
  • refusing help or care.

Doctors and nurses can use a tool to assess whether these behaviours may be 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 to make decisions about whether to give the person painkillers.

Painkillers are usually tablets or capsules. The person you care for may have problems swallowing medicines or remembering to take them. In this situation, they can be given painkiller patches that stick to the skin.

You can do some simple things to help with pain and discomfort. You could try:

  • changing their position
  • using heat pads, hot-water bottles or ice packs
  • giving them a massage.

Sometimes the person 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 will 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 can be different reasons why someone is not 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.

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

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 symptoms or side effects of cancer treatment. You may also be able to get equipment that could make them more comfortable, such as a pressure-relieving mattress.

Some people find that anxiety, worry and emotional distress is 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 more information about talking with someone who has cancer, including tips on how to start a conversation and listening to someone.

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

Using a symptom diary

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

Back to Dementia and cancer

Advanced cancer and dementia

If it is not possible to control the cancer, the person you care for will be able to have treatments to manage any symptoms.