How can cancer impact someone’s personality?

There isn’t a “right” way to deal with cancer. Sadness, anger, hope, numbness, fear, determination, denial: the list of feelings you might experience along the journey is endless, and you have every right to feel them. However, if you notice a very sudden change in your own behaviour, or someone you care for seems very different since their diagnosis or treatment, there might be something else going on too.

Here are some of the things you might notice.  

  • Depression and “flat” emotions
  • Anxiety
  • Mood swings
  • Irritability or aggression
  • Apathy (lack of interest and motivation)
  • Confusion and forgetfulness
  • Lack of inhibitions – behaving in socially or culturally unacceptable ways
  • Difficulty planning and organising
  • Difficulty concentrating
  • Difficulty identifying emotions in yourself and others

Of course, every person is different – and everyone will react differently to the difficult experiences cancer brings. For some people, any “personality changes” might just be a totally normal reaction to a life-changing event, but there are other factors that could be affecting someone’s behaviour.

Why might personality changes happen in cancer?

cancer survivor personality changes

Mental health

Nobody is going to feel okay when they’re told they have cancer. Feeling extreme emotions after hearing bad news or when going through illness and treatment is completely understandable, and it’s important to feel these emotions instead of trying to hide them. But if they’re getting in the way of your day-to-day life, your recovery, or enjoying time with your friends and family, you don’t have to “just get on with it” – there are lots of ways to get help and feel a little bit better.

Worry and anxiety

Stress and anxiety aren’t just in your mind. They can have real, physical effects on your body too. When you’re very anxious you might find that you have trouble sleeping, or you may feel sweaty or nauseous. Some people might even experience panic attacks or shortness of breath. These feelings might be more intense in the run up to appointments or when waiting for results, or they may come and go at seemingly random times.


Feeling sad and low when you have cancer is a normal response to a horrible situation. But feeling continuously low or unable to function for more than a couple of weeks, or having thoughts of harming yourself, could be a sign that you’re experiencing depression.

Mental health problems are really, really common, and they are even more common amongst people coping with long term illnesses such as cancer. The most important thing to remember is that mental health problems can be easily treated – even if you have cancer. You don’t have to suffer from anxiety, depression or other mental health issues on top of your illness. And getting the right help and support for your mental health could help you feel more equipped to face the other aspects of cancer.

What can I do?

Talking to your doctor about emotional issues as well as physical ones will give them a better overview of how things are going. They may be able to prescribe you medications that will help with anxiety and depression, and they may also refer you for counselling or therapy if you feel it would be helpful to talk. You might also find it helpful to think about some techniques proven to help with managing anxiety and depression, such as mindfulness, CBT or gentle exercise.

Chemo brain and personality changes


chemo rage picture - woman experiencing chemo anger

We hear so often from our community about their struggles with chemo brain. The feeling of “mental fog”, difficulty concentrating or remembering things, and other cognitive issues can really impact someone’s life, and are a common personality change after chemo. However, another phenomenon we sometimes hear about is “chemo rage”.

Chemo rage

Anger is a completely reasonable response to cancer and the many difficulties it brings. But for some people, their cancer treatment is accompanied by a sudden, uncharacteristic increase in irritability, angry outbursts, and even aggressive behaviour. This can be really alarming and upsetting for both the person going through cancer and their loved ones.

What’s going on?

Though this behaviour might be a purely emotional reaction, there is also the possibility that it may be influenced by medications and treatment. Often, cancer treatments are accompanied by steroids, to make the therapy more efficient and to manage some side effects. Unfortunately, a potential side effect of steroids themselves is an increase in mood swings, and particularly in irritability and anger – sometimes called “roid rage”.

If you recognise this behaviour in yourself, or suspect that someone you care for is having this reaction to steroids, the answer is (as always!) to talk to your doctor. Please don’t stop taking any medications or change your dosage – your doctor will be able to advise you, talk through your options and potentially prescribe something to counteract this side effect.


Hormones and the endocrine system

Personality changes in cancer may also be due to impacts on the body’s hormones. Hormones are chemicals released by your body that help to keep it functioning. They control our metabolism (how we produce and use energy), how we respond to changes in our environment, our sexual functioning and our mood.

So if cancer or its treatment interferes with the hormonal system, this can have a huge effect on your body and how you feel, both physically and mentally.

For example, low testosterone levels have been linked to increased irritability in men – we’ve heard it described as “what makes grumpy old men grumpy”. Likewise, we know that reproductive hormones can have effects on mood, appetite and metabolism, in both men and women.

As well as causing problems in your body’s own hormonal systems, some cancers can also release their own hormones into the bloodstream, causing their own side effects. It’s worth talking to your doctor about hormones and how they might be affecting your or your loved one’s mood, behaviour and personality.

Changes in your brain

Your brain is the computer that runs your whole body. It’s constantly sending and receiving information to and from every part of you, controlling all the systems that keep you going. It also processes all your memories, thoughts, feelings and behaviour. So if your brain is affected by cancer or its treatment, it’s likely that you will experience some changes in personality. These may be temporary or more long term, and can be very scary to deal with.

Brain changes can come about as a result of a brain tumour, or due to brain swelling following treatments such as chemotherapy. The experience many patients describe as “chemo brain”  is also an example of cognitive (thinking) and emotional changes due to alterations in the brain’s structure and chemistry.

Similar personality changes may also happen if a person’s liver is failing. If the liver isn’t able to remove all the harmful chemicals in the blood, these “toxins” can build up and enter the brain. This is called hepatic encephalopathy (HE), and can come about suddenly if the liver shuts down, or more slowly as a result of long term liver damage. HE is a treatable condition, so it’s important to recognise the signs and get medical advice as soon as possible.

What can I do?

If you or someone you care for is experiencing personality changes, there is a lot that can be done to try and manage the condition. Your doctor may be able to prescribe steroids to reduce brain swelling. Medications or therapy for anxiety, irritability and depression can also help things to feel more normal again.

Caring for someone with personality changes

caring for someone with cancer personality changes

Experiencing personality changes with chemo or cancer may be scary and upsetting, not only for the person going through cancer but also for their loved ones and carers. You might find that you experience more conflict in your relationships, or it might be hard for you to communicate as easily as you did before.

At times like this, it’s important to get all the support you can, from friends, family, support groups or even the online community. Talking to other people who understand will help you feel less alone, and can remind you of all the good things about the person you’re caring for, even when times are really tough.

Though personality changes in cancer may happen for many reasons, from mental health to chemical changes in the body, it doesn’t really change what you or friends, family or carers have to cope with. Seeing someone act differently to the person you know and love can be very distressing, and of course being that person can be scary too.

What can I do?

mindfulness for cancer personality changes picture

When we were researching this article, one tip we found in the online cancer community really stuck with us. It was posted as a response to a lady struggling to communicate with her father after his cancer treatment.

“My only suggestion is to write him a letter, telling him how much you love him, and maybe recalling some happy things you have done together. You don’t have to make it gloomy, just put down your feelings. Then he can read it when he feels like it, and perhaps respond when he feels like it. Sometimes our clams who find it hard to talk about their feelings can be more easily reached at one remove.”


We thought this was a wonderful suggestion for anyone finding it difficult to deal with changes in a loved one’s personality. We’d love to hear any ideas you have for coping with personality changes and cancer, too. You can share them with us and our whole community on our Facebook or Twitter pages, or by emailing us at

Whether the personality changes you’re experiencing are a medical issue or simply a completely understandable reaction to a life-changing event, the best and most important thing you can do is to talk to someone about them. Getting advice from your doctor on possible treatments, medications, and therapy is the first step, and there are many other sources of support out there too.