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Side effects of radiotherapy

Find out about the side effects of radiotherapy and how to cope with them.

Side effects tend to start a few days after the radiotherapy begins. They gradually get worse during the treatment. They can continue to get worse after your treatment ends. But they usually begin to improve a few weeks following your treatment.

It may take up to 6 weeks before the mouth or throat soreness completely goes. Getting over a long course of treatment completely can take several months. 

Everyone is different and the side effects vary from person to person. You may not have all of the effects mentioned.

Side effects can include:

You are likely to feel very tired during your treatment. It tends to get worse as the treatment goes on. You might also feel weak and lack energy.

After a while you might need to sleep after each radiotherapy session. Rest when you need to.

Tiredness can carry on for some weeks after the treatment has ended but it usually improves gradually.

Various things can help you to reduce tiredness and cope with it, such as exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

You might feel sick at times. You can have anti sickness medicines. Let your treatment team know if you still feel sick, as they can give you other medicines.   

Your skin might go red or darker in the treatment area. You may also get redness or darkening on the other side of your body. This is where the radiotherapy beams leave the body. 

The red or darker areas can also feel sore. Your radiographers will give you creams to soothe the skin. The soreness usually goes away within 2 to 4 weeks of ending the treatment. But your skin might always be slightly darker in that area.

Tell the radiotherapy staff if you notice any skin changes.

Your mouth and throat might get sore. It may be painful to swallow drinks or food. You will have mouth washes to keep your mouth healthy.

You can have painkillers to reduce the soreness. Take them half an hour before meals to make eating easier.

Tell your doctor or nurse if your throat is sore.

During and after treatment, you might have difficulty swallowing.

Ask to see a dietitian if you have problems with eating and drinking. If you can still swallow you can drink liquid feeds. If it is too painful to swallow you may need tube feeding.

You can have feeds through a nasogastric tube that goes up your nose and down into your stomach. Or you can have a PEG tube that goes through the skin into your stomach. Your nurse will show you or your relatives how to give the feeds. 

Tips for eating and drinking:

  • Drink about 3 litres of water a day while having treatment.
  • Eat soft foods.
  • Eat slowly and avoid eating late in the day.
  • Drink plenty during and after meals to soften your food.
  • Eat small amounts often rather than big meals.
  • Try different foods to find out which are easiest to swallow.
  • You can have high calorie drinks to boost your calorie intake if you need them.
  • You might need to have liquid food into your vein or through a tube into your nose or stomach if you can’t eat enough.

Your mouth might get very dry, which can be uncomfortable. Various things can help.


  • Try to drink at least 3 pints (one and a half litres) of fluid a day
  • Choose meals that are moist.
  • Use gravies and sauces to make swallowing easier.
  • Take regular sips of water with your meal to help you chew and swallow your food.
  • Suck small amounts of ice chips to refresh your mouth.
  • Chew sugar free chewing gum.
  • Try eating fresh pineapple.
  • Get your doctor or nurse to give you medicines to stimulate your salivary glands.
  • Ask your doctor about artificial saliva products, such as tablets, mouthwashes, gum, pastilles, and toothpaste.
  • Radiotherapy to the head and neck can cause damage to the salivary glands. This can make your mouth very dry. Your doctor can prescribe artificial saliva and medicine to stimulate your salivary glands. 
  • It is very important to have regular check ups with your dentist.

Your voice might become hoarse as you go through your radiotherapy. Depending on the area being treated your voice may disappear altogether. It will come back, but may sound different afterwards. 

Radiotherapy might affect your sense of smell. This is because radiotherapy causes dryness of the mouth and nose. If your nose is very dry you will not be able to smell things normally for a while. 

Radiotherapy can damage the nerve that control the muscles that move our mouth. This problem is called trismus. Your doctor or nurse will give you exercises to help strengthen your muscles. 

Food may taste metallic.


  • Choose foods that have strong flavours, such as herbs, spices, marinades and sauces if all your food tastes the same.
  • Season your food with spices or herbs, such as rosemary, basil and mint.
  • Garnish cold meat or cheese with pickle or chutney.
  • Try lemon or green tea if tea or coffee taste strange.
  • Sharp tasting fizzy drinks such as lemonade or ginger beer are refreshing.
  • Some people find that cold foods taste better than hot foods.

After radiotherapy to treat a head and neck cancer, you are at risk of getting swelling called lymphoedema in your neck or face.

Lymphoedema in the head or neck area might also cause swelling of your tongue and other parts of your mouth.

Tell your doctor if you:

  • have any swelling in the head or neck area or a feeling of fullness or pressure
  • find it difficult to swallow
  • have changes in your voice

Side effects if you have chemotherapy with radiotherapy

Chemotherapy combined with radiotherapy can make some side effects worse. Combining these treatments is called chemoradiotherapy.

Last reviewed: 
14 Oct 2014
  • Cancer and its management (7th edition)
    J Tobias and D Hochhauser 
    Blackwell, 2015

  • Lymphedema Outcomes in Patients with Head and Neck Cancer
    B Smith and others
    Otolaryngology Head and Neck Surgery. 2015 February; 152(2): 284–291.

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