Diabetes and chemotherapy

Chemotherapy can affect your blood sugar if you have diabetes. Find out more about this and other side effects.

Chemotherapy and your blood sugar

Chemotherapy uses anti-cancer (cytotoxic) drugs to destroy cancer cells. You may have 1 chemotherapy drug or a combination of different drugs. Chemotherapy is usually given as a few sessions of treatment, with rest periods in between.

When you have chemotherapy, your blood sugar level may get too high or too low. This is because of the side effects of chemotherapy, such as sickness, diarrhoea and loss of appetite. This can make your diabetes diffcult to manage.

Some chemotherapy drugs, such as asparaginase and busulfan, can cause your blood sugar level to rise. Your cancer doctor, specialist nurse or specialist pharmacist will tell you more about the drugs you will take. Chemotherapy is often given with steroids which can affect your blood sugar level.

Controlling your blood sugar during chemotherapy

Before you start chemotherapy, talk to your doctors and nurses about any side effects you may have. Ask them for information about the best way to manage your diabetes during treatment. This is particularly important if your treatment includes taking steroids.

You may need to check your blood sugar levels more often than normal. You may need to make changes to your diabetes treatment. Your diabetes team will help you to do this. For example:

  • if you use insulin, you may need to change the dose or type of insulin you use.
  • if you manage your diabetes with tablets, your specialist may suggest changing the dose – they may ask you not to take them on the day of your treatment.
  • if you manage your diabetes with your diet, you may still find that your blood sugar level increases – you may need to start diabetes medication.

Tell your diabetes team if you are not manging to eat or drink as much as usual. This may be because you are feeling sick or have a sore mouth. Also tell them if you develop diarrhoea. We have more information about managing sickness and about sick day rules when you are feeling unwell. Diabetes UK also have more information about this.

It is important to tell doctors how well you are managing to control your blood sugar level during your chemotherapy. If you are finding it difficult, your cancer doctor may adjust your diabetes medication after speaking to the diabetes team. Your doctors will talk to you before making any changes. You should always check your blood sugars if you feel unwell. Talk to your cancer doctor or specialist nurse if you are not sure.

You should talk to your doctor if your blood sugar levels are:

  • always 10mmol/l or higher, and you feel unwell
  • less than 4mmol/l on more than 2 occasions.

Damage to the nerves (peripheral neuropathy)

Some chemotherapy drugs can damage the nerves in your body. This can lead to pain and a change in sensation called peripheral neuropathy. The pain can sometimes be worse if the nerves are already damaged by diabetes. Peripheral neuropathy caused by chemotherapy does not usually last long, but it can sometimes be permanent.

The chemotherapy drugs most likely to cause peripheral neuropathy are:

Talk to your cancer doctor or specialist nurse if you are worried about peripheral neuropathy. They can give you more information about your treatment and advice on the best way to manage any pain. Your GP can also give you advice and support.

About our information

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.

  • References

    Below is a sample of the sources used in our diabetes and cancer treatment information. If you would like more information about the sources we use, please contact us at informationproductionteam@macmillan.org.uk

    Joint British Diabetes Societies for inpatient care (JBDS-IP). The management of glycaemic control in people with cancer. 2023.

    Joharatnam-Hogan, N; Chambers, P; Dhatariya, K; and Board, R. The Joint BritishDiabetes Society for Inpatient Care (JBDS), UK Chemotherapy Board (UKCB). A guideline for the outpatient management of glycaemic control in people with cancer. Diabetes Medicine. 2022; 39.1-11. Available from: https://doi.org/10.1111/dme.14636 [accessed Oct 2022].

    Shahid, R.; Shahid, A.; Duc, L; and Sunil, Y. Diabetes and Cancer, Risks, Challenges, Management and Outcomes. MDPI. 2021;13:1-21. Available from: www.ncbi.nlm.nih.gov/pmc/articles/PMC8616213 [accessed Oct 2022].

Date reviewed

Reviewed: 01 September 2026
Next review: 01 September 2026
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