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Interferon (Intron A)

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This page tells you about the biological therapy interferon alpha and its possible side effects. There are sections about


What interferon is

Interferon alpha is a man made copy of a substance that some types of white blood cell make naturally in the body. The blood cells make interferon as part of the immune response when the body reacts to infection or to cancer.

Interferon works in several ways. It interferes with cancer cells and stops them growing and multiplying. And it stimulates the immune system by encouraging killer T cells and other cells to attack cancer cells. It also encourages cancer cells to send out chemicals that attract immune system cells to them.

Interferon is used to treat several different types of cancer, particularly kidney cancer (renal cell cancer), malignant melanoma, multiple myeloma and some types of leukaemia. It is also used to treat diseases other than cancer.


How you have interferon

Interferon is given into the bloodstream or by injection. It is most often given by injection just under the skin (subcutaneously) into the abdomen (tummy) or thigh. How often you have it depends on which cancer you have. It can be given daily, although it is most often given 3 times a week. If you are having interferon for some weeks or months, you can be taught to give the injection yourself at home. Or a family member can learn how to do it. You should keep your interferon in the fridge.

You should tell your doctor if you have

  • Shingles or exposure to someone with chickenpox (interferon treatment may make this flare up)
  • Heart disease

The side effects associated with interferon alpha are listed below. You can use the links (underlined) to find out more about each side effect. Where there is no link, the information in the cancer drugs side effects section may be helpful. Or you can click on search at the top of the page.


Common side effects

More than 10 in every 100 people have one or more of the side effects listed below.

A temporary drop in the number of blood cells made by the bone marrow. This can cause

  • An increased risk of getting an infection from a drop in white blood cells – it is harder to fight infections and you can become very ill. You may have headaches, aching muscles, a cough, sore throat, pain passing urine or feel cold and shivery
  • Tiredness and breathlessness due to a drop in red blood cells (anaemia) – you may need a blood transfusion
  • Bruising more easily due to a drop in platelets – you may have nosebleeds, bleeding gums after brushing your teeth, or lots of tiny red spots or bruises on your arms or legs (known as petechia)

Some of these side effects can be life threatening, particularly infections. You should contact your doctor if you have any of these side effects. Your doctor will check your blood counts regularly to see how well your bone marrow is working.

Other common side effects include

  • Tiredness (fatigue) during and after treatment – most people find that their energy levels are back to normal from 6 months to a year after their treatment ends
  • Flu like symptoms, including fever, chills, a headache, aching muscles and joints – nearly everyone taking interferon has this side effect at first. It usually gets better as your course of treatment continues. These symptoms usually begin 2 to 4 hours after your injection and last for about 12 hours. Take paracetamol before your injection and every 4 to 6 hours afterwards for as long as you need to. But don't take more than 8 tablets in 24 hours. You can try having your injection and paracetamol before you go to bed to see if that helps
  • Feeling or being sick – this happens to about half the people treated. Your doctor or nurse will give you anti sickness medicines (anti emetics). Let them know if it is not controlled as you could try other anti sickness drugs
  • Diarrhoea – you should drink plenty of fluids. If diarrhoea is severe or continues you could get dehydrated, so tell your doctor or nurse
  • Loss of appetite – this may increase as your course of treatment goes on
  • Taste changes or a metallic taste in your mouth
  • Depression or emotional changes such as anxiety
  • Difficulty sleeping
  • A sore throat and pain on swallowing
  • Weight loss
  • Itchy, dry skin or rashes
  • Sudden muscle or joint pain – let your doctor or nurse know if you have this

Occasional side effects

Between 1 and 10 in every 100 people have one or more of these.

  • Itching at the injection site
  • Hair thinning – this is more likely to happen with long courses or high doses of interferon
  • Depression, confusion or extreme sleepiness – this is more common in older patients or people who have had depression before. Tell your doctor if you have these symptoms
  • Liver changes that are very mild and unlikely to cause symptoms – the liver will almost certainly go back to normal when treatment is finished, but you will have regular blood tests to check how well your liver is working
  • Damage to heart muscle, which is usually temporary but for a small number of people may be permanent – your doctor will check your heart before and after your treatment
  • Loss of fertility – you may not be able to get pregnant or father a child after treatment with this drug. It is important to talk to your doctor about your fertility before starting treatment. 
  • Women may stop having periods (amenorrhoea) – this may only be temporary
  • An allergic reaction to the drug – let your doctor or nurse know immediately if you have swelling of the hands, feet, ankles, face, lips, mouth, or throat or any difficulty in swallowing or breathing
  • Feeling thirsty and a dry mouth – drink plenty of fluids and brush your teeth at least twice a day to prevent dental problems
  • High blood pressure
  • Worsening of migraines
  • Low sex drive
  • Indigestion (heartburn)
  • Constipation

Rare side effects

Fewer than 1 in 100 people have these effects.

  • Eye inflammation (conjunctivitis)
  • Sleepwalking
  • Sweating
  • Fine shaking movements

Important points to remember

The side effects above may be mild or more severe. A side effect may get better or worse through your course of treatment, or more side effects may develop as the course goes on. This depends on

  • How many times you've had the drug before
  • Your general health
  • The amount of the drug you have (the dose)
  • Other drugs you are having

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. They can give you advice or reassure you. Your nurse will give you a contact number to ring if you have any questions or problems. If in doubt, call them.

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies – some drugs can react together.

Interferon may have a harmful effect on a baby developing in the womb. It is not advisable to become pregnant or father a child while taking this drug. Discuss contraception with your doctor or nurse before having the treatment.

Breastfeeding is not advisable during this treatment because the drug may come through in the breast milk.



You should not have immunisations with live vaccines while you are having treatment or for at least 6 months afterwards. In the UK, these include rubella, mumps, measles (usually given together as MMR), BCG, yellow fever and Zostavax (shingles vaccine).

You can have other vaccines, but they may not give you as much protection as usual until your immune system has fully recovered from your treatment. It is safe to have the flu vaccine.

It is safe for you to be in contact with other people who've had live vaccines as injections. There can be problems with vaccines you take by mouth (oral vaccines), but not many people in the UK have these now. So there is usually no problem in being with any baby or child who has recently had any vaccination in the UK. You might need to make sure that you aren't in contact with anyone who has had oral polio, cholera or typhoid vaccination recently, particularly if you live abroad.


More information about interferon

This information does not list all the very rare side effects of interferon alfa that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at

If you have a side effect not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at

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Updated: 13 March 2013