Coping with the side effects of treatment when you have diabetes

Cancer and its treatment can cause side effects that can make it difficult to manage your diabetes. These side effects may include:

  • feeling and being sick
  • diarrhoea
  • appetite changes
  • infection
  • slow wound healing.

You may also be more tired (fatigued) and be less active than normal. Not being active can change your blood sugar levels.

These side effects can make your blood sugar levels go too high or too low. You may have to check your blood sugars more often.

Tell your doctor or nurse if you have any of these side effects or if they get worse. They will be able to suggest ways to manage them and help you control your blood sugar levels. If you usually control your diabetes with your diet, you may need to start taking medicines. Or you may need to adjust your dose of insulin or stop taking diabetes tablets while you have side effects. Your diabetes team can give you more advice.

Feeling sick and being sick

Cancer or its treatments can sometimes make you feel sick or be sick. Chemotherapy, radiotherapy, hormonal therapy and targeted therapy can all cause sickness. Physical changes can cause these side effects too. For example, this might be because of damage to the liver or pressure on the brain. If you’re feeling anxious about cancer and your treatment, this can also make you feel or be sick.

There are many different types of drugs that help treat sickness. These are called anti-emetics. They can be given as a tablet, an injection, a suppository or a skin patch. If you’re having a cancer treatment which is known to cause sickness, you should start taking anti-emetics before your treatment starts.

Being sick can be a problem when you have diabetes. Because you may not be able to eat or drink, you could become dehydrated. This can be more serious for people with diabetes.

You will need to check your blood sugar more often, possibly every two to four hours. You may need to check for ketones if your blood sugar is very high and you use insulin to control your diabetes. Ketones are chemicals that can sometimes build up in the body when there is a severe lack of insulin. Ketones are toxic to the body and large amounts can be very serious. If you have ketones, you should contact your diabetes team for advice straight away.

If you use insulin, you will usually have this before eating. But if you are sick, you may not absorb enough food and your blood sugar may drop too low. If you are sick after eating, check your blood sugar and try to eat something to stop the blood sugar getting too low. It is a good idea to have a fast-acting carbohydrate to hand, such as glucose tablets, sweets or fruit juice.

If you are being sick, you may need to change the dose of your insulin or change the type of insulin you use. You should not stop taking it.

If you use tablets to manage your diabetes, you may need to stop taking them while you are being sick. Your diabetes team can give you more advice.

Tips to help you cope with sickness

  • It is important to plan ahead. Before you start any cancer treatment, talk to your cancer doctor or specialist nurse. Explain that you have diabetes and that you need to prevent sickness as much as possible.
  • Ask your diabetes team for advice about managing sickness before it happens. They can tell you how to manage your diabetes when you are ill, known as the 'sick-day rules'. It is helpful for family or friends to know how to manage things too.
  • Take your anti-sickness medicines as they are prescribed, even if you are not feeling sick. It is easier to prevent sickness before it starts than control it.
  • Tell the doctor if the anti-sickness medicines are not working. They can give you different medicines that may work better.
  • Try to stick to your normal diet and eat the same amount of carbohydrates that you normally do. But if you are struggling to do this, it is okay to eat foods you wouldn’t normally eat.
  • Try eating dry foods and avoid greasy, fatty or fried foods.
  • Ginger can help reduce sickness. Try drinking ginger tea or eating ginger biscuits.
  • Eat cold foods, such as yogurt and ice cream, or foods at room temperature, such as tinned fruit, dry toast and plain biscuits.
  • If the smell of cooking makes you feel sick, eat cold meals or food from the freezer that only needs heating up.
  • If feeling sick is putting you off food or you can’t keep food down, replace meals with snacks or drinks that contain carbohydrates, such as glucose tablets, fruit juice or non-diet fizzy drinks.
  • Try to keep drinking even if you can’t manage to eat. Aim to drink a cup of fluid every hour.

If you can’t keep any fluids down, contact the hospital as soon as possible. It is important to prevent dehydration.

You should talk to your diabetes team if you are worried about coping with sickness. They will be able to give you more advice.

I didn't have many problems with nausea. When I had slight nausea, I would eat a couple of dry biscuits. I was then able to keep my sugar levels pretty stable.



Diarrhoea means that you need to pass more bowel motions a day than is normal for you, and the stools (poo) you pass are looser than normal. It can be caused by chemotherapy, radiotherapy, targeted therapies and surgery. Sometimes other medicines, such as antibiotics, or an infection can also cause diarrhoea.

Some people with diabetes may already have diarrhoea. It can happen because the nerves that control bowel movements are damaged by high blood sugar levels (gastroparesis), but this is rare. If you already have diarrhoea, your symptoms could get worse during cancer treatment.

Your doctor or specialist nurse can tell you if you are likely to get diarrhoea because of your cancer treatment. They will tell you what you need to do if this happens.

Most diarrhoea caused by treatment is mild. But for some people, it can be severe and may lead to dehydration. It is important to avoid dehydration. Tell your doctor if you have diarrhoea or if it is getting worse. They can find out what might be causing it and give you anti-diarrhoea medicines.

If you have diarrhoea more than 4 to 6 times a day, contact the hospital on the numbers you have been given and speak to a doctor or nurse. Check it is safe to keep taking the medicines you have been prescribed, as some may need to be temporarily stopped if you are very dehydrated.

Tips to help you cope with diarrhoea

  • Drink plenty of liquid (up to two litres a day).
  • Avoid alcohol and coffee.
  • Eat small, frequent meals of light foods, such as white fish, chicken, well-cooked eggs, white bread, pasta and rice.
  • Cut down on high-fibre foods, such as cereals, raw fruit and vegetables.
  • Eat your meals slowly.

If your diarrhoea is caused by radiotherapy or chemotherapy, changing your diet may not help. A dietitian can give you more advice about this. It’s important to take the anti-diarrhoea medicines your doctor gives you.

If you have diarrhoea after surgery for bowel cancer, talk to your doctor, specialist nurse or a dietitian about what may help.

Loss of appetite

During cancer treatment, you may lose your appetite because you feel sick, you are too tired to eat, or foods taste different. This is usually a temporary side effect.

If you have diabetes and are unable to eat enough, your blood sugar may drop too low. This can lead to hypoglycaemia, known as a hypo. It's important to be aware of the early signs of a hypo, so you can treat it quickly. Make sure your family and friends are also aware of the symptoms, so they can help you.

Symptoms of a hypo include:

  • sweating
  • feeling dizzy
  • fatigue (extreme tiredness)
  • feeling weak
  • looking pale
  • confusion
  • a faster heart rate than normal.

A good way to avoid a hypo is to eat regularly. If you can’t eat solid food, you could sip sugary drinks.

While you are not eating your normal diet, you will need to check your blood sugar more regularly than normal. If your blood sugar level starts to decrease or you develop symptoms of a hypo, try eating or drinking a fast-acting carbohydrate, such as glucose tablets, sweets or fruit juice.

While you have a poor appetite, you may need to change your dose of insulin or tablets to help prevent hypos.

Your diabetes team can give you advice about avoiding hypos and how to manage them if they happen.

Tips to help improve your appetite

  • Eat small amounts as often as possible. If you find your appetite is better at certain times of the day, make the most of this. You may need to change your diabetes medicines.
  • Keep snacks handy. Bags of nuts, crisps or dried fruit, or a bowl of grated cheese, are light and tasty. If these are hard to swallow, try yoghurt or fromage frais. If you’ve recently had surgery or radiotherapy for bowel cancer, you may need advice about the best foods for you. Talk about this with your specialist nurse or doctor, or a dietitian.
  • Try sweet or savoury nourishing drinks. These can replace small meals and can be sipped slowly through the day.
  • Eat your meals slowly. Chew the food well and relax for a bit after each meal.

Bigger appetite than normal

Some medicines, such as steroids, may make you want to eat much more than usual. It’s important to try to eat healthy foods as much as possible. Try to avoid foods that are high in carbohydrates and sugar, such as biscuits and sweets.

A balanced, heathy diet will help you avoid putting on too much weight. Having a healthy weight is important for managing your blood sugar levels.

We have more information to help you cope with eating problems and maintain a healthy lifestyle.

Diabetes UK has more information and recipes to help you try to maintain a healthy weight.

I live on my own and sometimes don’t have the energy to cook. I can’t have ready-made stuff because it has a lot of sugar in it. A veggie stir-fry is good to try because it’s healthy, cheap and quite easy.


Lack of activity

Being active is an important part of a healthy lifestyle. It can help to:

  • reduce tiredness and some side effects of cancer treatment
  • reduce anxiety and depression
  • improve your mood and quality of life
  • strengthen your muscles, joints and bones
  • look after your heart and reduce the risk of other health problems.

Being active can also help with your diabetes by:

  • helping the body use insulin more effectively
  • increasing the amount of sugar used by the body
  • improving how you manage your diabetes
  • helping you manage your weight.

During cancer treatment, there may be times when you don’t feel like being active – and that is okay. You may feel very tired (fatigued) or not have much energy. You may also have side effects, such as sickness or pain, that stop you being active.

If you have diabetes, not being active can change your blood sugar level. This will depend on your situation, but you may need to test your blood sugar more often.

Your diabetes team can give you advice about managing your blood sugar while you are less active.

Ways you can be active

Choose activities you enjoy and try to do a mix of activities. You could try:

  • Aerobic exercises, such as walking, dancing, running, cycling or swimming. These are good for your heart.
  • Resistance exercises, such as lifting small weights or ‘sit to stand’ exercises that you can do at home. These help to strengthen muscles.
  • Flexibility exercises, such as stretches, yoga, Tai Chi and Qigong. These can improve suppleness.
  • Balance exercises, such as yoga, Tai Chi, Pilates and Qigong. These can help with balance and strength.

Tips to help you get more active

  • Join an activity group or association.
  • Walk or cycle to the shops.
  • Keep a record of how active you’ve been.
  • Set goals you can achieve.
  • Take up activities you enjoy.
  • Tell your friends about it. They may want to join you.

We have more information and a range of tools to help you get more active.

Risk of infection

The immune system protects the body from harmful bacteria and other organisms. Some types of cancer and its treatment can weaken your immune system, which can increase your risk of developing an infection:

  • Chemotherapy, radiotherapy, targeted therapy and some types of cancer can reduce the number of white blood cells your body produces. White blood cells fight infection.
  • Surgery makes a break in the skin. Our skin helps protect us from infection.

People with diabetes may be more at risk of developing an infection or a weaker immune system, especially if their blood sugar level is often too high. Your diabetes team can give you advice if you have problems keeping your blood sugar level under control.

During an infection, the body tries to fight it by releasing extra sugar into the blood. If you don’t have diabetes, the pancreas will make more insulin to cope with the extra sugar. But if you have diabetes, the extra sugar will cause high blood sugar levels. This can make you feel more thirsty and pass more urine, which can lead to dehydration.

Symptoms of an infection include:

  • a high temperature
  • suddenly feeling unwell, even with a normal temperature
  • a painful, swollen or hot wound
  • feeling shaky or shivering
  • a sore throat
  • a cough
  • diarrhoea
  • needing to pass urine a lot.

If you develop any of these symptoms, it is important to talk to your doctors as soon as possible. They can give you antibiotics to fight the infection and help control your blood sugar level.

If you have an infection, you will need to check your blood sugar level more often. If you usually control your diabetes with diet, you may need to start taking medicines. If you already take medicines, you may need to change the dose. Talk to your diabetes team if you have an infection and your blood sugar level is high.

Tips to help you avoid infection

  • Have good personal hygiene. Wash your hands regularly with soap and hot water, especially after going to the toilet or before preparing a meal.
  • Have a shower or bath every day, and don’t share towels.
  • Avoid people with sore throats, colds, flu, diarrhoea or vomiting, or infections such as chickenpox. If you have contact with someone who has an obvious infection, ask your cancer doctor or nurse for advice.
  • Stay away from crowded places as much as possible.
  • Avoid using public swimming pools, jacuzzis or changing rooms. If you are doing sports or social activities, try to go at quieter times.
  • Be careful if you have pets or work with animals. If you can, avoid handling any animal waste, such as litter trays or manure.

We have more information about avoiding infection.

Slow wound healing

After an operation, your wound will be closed using stitches or clips. These are usually removed after about 7 to 10 days. Some stitches are designed to slowly dissolve as the wound heals.

How long the wound takes to heal depends on the operation you have had. If you only had a small area of tissue removed, your wound will usually heal quickly. If you have had a bigger operation, it may take a few weeks to heal properly.

Wound healing can be slower if you:

  • are older
  • have an unhealthy diet
  • smoke or use nicotine replacement
  • are having cancer treatment, such as chemotherapy.

If you have diabetes and your blood sugar level is high, your wound can take longer to heal. Wound healing may also be slower in people who have had diabetes for many years. Over time, high levels of blood sugar can affect the nerves and lead to poor blood circulation and nerve damage. Wounds need a good blood supply to heal.

The longer a wound takes to heal, the more risk there is that it will become infected.

It is important to keep the wound clean and dry, to help it heal and prevent infection. After an operation, the wound will be covered with a dressing for a day or two. The ward nurses will change the dressing before you go home and tell you how to look after the wound when you are at home. If needed, the ward nurses will make you an appointment with your practice nurse, or arrange for a district nurse to visit you at home.

Contact the hospital doctor if you develop any symptoms of a wound infection.

Tips to help with wound healing

  • Keep your blood sugar levels under control – ask your diabetes team for help if you are having problems.
  • Get plenty of rest and sleep.
  • Don’t smoke.

It’s important to eat a well-balanced diet, especially food that contains lots of:

  • protein – meats, beans, eggs and dairy products
  • vitamin A – dark green, leafy vegetables, orange and yellow vegetables, liver and cereals
  • vitamin C – citrus fruits, broccoli, spinach, tomatoes and baked potatoes
  • zinc – seafood, red meats and fortified cereals.