Diabetes and chemotherapy

How treatment affects diabetes

Chemotherapy can make you feel sick or be sick. You might not want to eat and this can be a problem. If you can't eat, your blood sugar could drop too low causing:

• faintness

• sweating

• coma

This is called a hypoglycaemic attack.

Planning chemotherapy

You and your doctor might need to plan chemotherapy a bit more carefully if you are diabetic. Some chemotherapy combinations include steroids and these might upset your blood sugar. Your doctor might ask you to have a blood test to check your sugar levels before you start treatment.

It might be a good idea to talk to your diabetes specialist before you start chemotherapy. They might suggest that you check your blood sugar levels more often. Or if you don’t already check them, that you should start. Your specialist might change your dose of diabetes medicine or switch it to something different. 

You can ask to see a dietitian if you are worried about your diabetes during chemotherapy.

Types of diabetes

There are 2 different types of diabetes. How you manage it depends on the type you have:

• type 1 – you need to have regular insulin injections or an insulin pump.

• type 2 – you may control it with either diet or with a combination of diet and tablets. Some people with type 2 diabetes also need to have insulin injections.

Type 1 diabetes

If you need insulin, you might have the first course of chemotherapy in hospital. This means that the nurses can keep an eye on you. Then, if you need sugar quickly, you can have it through a drip rather than by mouth.

It's possible for you to have insulin and a sugar solution (dextrose) together through a drip in hospital. The insulin dose is based on hourly or 2 hourly blood sugar tests. But most people don't need this.

Type 2 diabetes

If you control your diabetes with diet or tablets it should be possible to manage it during chemotherapy without many problems. Discuss it with your doctor, they might want to make some changes to your diabetes medicine. For example, they might suggest that you don’t take your diabetes tablets on chemotherapy days.

Side effects of chemotherapy and diabetes

You might lose your appetite and have to make an effort to have something to eat regularly. Also, you might feel sick because of your chemotherapy drugs. But there are very good anti sickness drugs available that can help. Take your anti sickness medicines before your treatment to try and prevent sickness.

It is important that you have good nutrition. Your doctor can prescribe you meals in a drink. They are rich in calories and you can sip them through the day. There are many different brands including Complan, Fresubin, and Build Up. 

Diabetes can affect your body's ability to fight infection. So you might be at a slightly higher risk of having an infection. Look out for signs of infection, such as a high temperature. Contact your advice line immediately if you are worried.

Find out more about symptoms of infections

Steroid induced diabetes

If you have steroids as part of your cancer treatment, it can sometimes lead to diabetes. This is called steroid-induced diabetes and is like type 2 diabetes.

This happens in people who were already at risk of developing diabetes. If you are at risk, you might need to monitor your blood sugar level while you are taking steroids.

Tell your healthcare team if you feel unwell or develop any of the symptoms of diabetes. These include:

• being very thirsty

• blurred vision

• passing urine often

• feeling very tired 

Your blood sugar level might reduce once you stop taking steroids. But sometimes the diabetes will still need treatment. If you are worried talk to your healthcare team. 

Find out more about diabetes and cancer at Diabetes UK