Weight loss medicine injections and your cancer treatment

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Information for patients

What is this information about?

This information is about weight loss injections such as Ozempic, Mounjaro and Wegovy (brand names for GLP-1 or Glucagon-Like Peptide-1 antagonists made by different companies) and how they can be harmful if you are having cancer treatment. 

It explains: 

• what you should do if you are taking these medicines and are having or due to start cancer treatment 
• why it is important for you to eat a balanced diet that gives you the nutrition you need if you have cancer  
• why GLP-1 weight loss medicines can be harmful if you are having cancer treatment 
• the side effects that you may get from taking GLP-1 medicines and what you must do if you get them 
• what you must do if you are due to have a medical procedure or operation that means you would need to have an anaesthetic (medicine so that you feel no pain or are drowsy or ‘sleeping’ during the procedure or operation). 

Why have I been given this information?

You have been given this information because:

• you are having GLP-1 injections or are thinking of starting them and 
• you are having or due to have cancer treatment. 

Reading this information can help you to get the nutrition you need so that:

• your body can cope as well as possible with your cancer treatment 
• cancer treatment doses and amounts (often based on your weight) are safe and work as well as possible. 

Can I keep using Ozempic, Mounjaro or Wegovy (GLP-1) weight loss injections during my cancer treatment?

Medicines such as Ozempic, Mounjaro and Wegovy are important in treating conditions such as diabetes and high blood pressure and helping people to lose weight. They can help with your health and wellbeing.

Do speak with your cancer care team before you start taking these medicines or continue to use them while you are having cancer treatment. Follow the advice that they give you. 

Why is what I eat even more important if I have cancer?

Eating a well-balanced, nutritious diet helps you to maintain your weight and muscle mass.   

When you have cancer, this can help you to:

• maintain your strength and energy levels 
• boost your immune system so that you can fight infections 
• cope better with your cancer treatment 
• improve your sense of wellbeing. 

Why might taking GLP-1 medicines be harmful to me if I am having cancer treatment?

If you are having weight loss injections, you may lose a lot of weight quickly.  

While you are having cancer treatments it can be harmful to: 

• lose weight that you did not plan to lose 
• lose a lot of weight 
• lose weight very quickly. 

All these things can happen if you are having weight loss injections. This is because they make you feel fuller, so you eat less.   

Losing weight can be useful for improving your general health and may have been a goal for you, but if you are having cancer treatments it can lead to: 

• Chemotherapy not working as well as it should. Your chemotherapy treatment is designed to be right for you, and your body weight, at the start of your treatment. If you lose a lot of weight during treatment: 
  • your chemotherapy dose may not be right any longer. We may need to adjust the dose. 
  • your body may not cope so well with the treatment. 
  • you may get more side effects.  

• Your radiotherapy treatment may need to be re-planned and could be delayed. Your radiotherapy plan is designed specially for you. It uses information from a CT scan that means we can target the tumour exactly.

If you lose a lot of weight or lose weight quickly your body shape changes. Your radiotherapy plan may no longer be right for your body shape. This means: 

• we may need to delay the start of your radiotherapy while we make a new radiotherapy plan or change your plan mid-way through your treatment. 
• you may need further scans before we can make a new plan for your radiotherapy. 

Should I tell my cancer care team about any side effects that I think may be caused by my weight loss injections?

Yes. Do tell a member of the team if you have any symptoms which may be side effects of weight-loss injections. These include:  

• nausea (feeling sick) or vomiting (being sick) 
• diarrhoea (thin, watery poos) 
• bloating (swollen, full or tight feeling in your tummy) 
• constipation (hard, dry poos that make it difficult and sometimes painful to poo).
• low appetite

Some cancer treatments such as chemotherapy, radiotherapy and immunotherapy can also cause these side effects. If you are having these treatments alongside weight loss injections:

• it may make the symptoms worse 
• it can be difficult for us to tell what is causing the symptoms and know how to treat them in the right way. 

What should I do if:

• I am having weight loss injections 

and

• I am due to have a planned medical procedure or operation (surgery) which would mean I need to have an anaesthetic? 

Do talk with your cancer care team about the benefits and risks of continuing with weight loss injections if you are due to have an operation or procedure which usually involves having an anaesthetic. 

Weight loss injections slow down your digestion. If you have an anaesthetic while you are on weight loss injections there is a higher chance that your stomach contents may come back up your ‘food pipe’ (oesophagus). They may get into your ‘air pipe’ (trachea) and lungs. This can:

• make it difficult for you to breathe because your airway is blocked 
• damage your air pipe and lungs because of the acid in your stomach contents 
• cause you to get a bacterial lung infection, such as pneumonia, which can be very dangerous. 

We advise most people who are on weight loss injections and due to have an anaesthetic to stop the injections 1 week before their operation or procedure. 

Who should I contact if I have questions or concerns after I have read this information?

Please contact your clinical nurse specialist.