Cancer drugs A to Z list
Peginterferon alfa 2a is an immunotherapy drug. Peginterferon alfa 2a is a possible treatment for some types of blood cancers called . These include polycythaemia vera (PV) and essential thrombocythaemia (ET).
You might also have peginterferon alfa 2a to treat conditions other than cancer, including hepatitis B and hepatitis C.
You pronounce peginterferon alfa 2a as peg-in-ter-feer-on-al-far-2-a.
Find out more about myeloproliferative neoplasms
Peginterferon alfa 2a stimulates cells of the to attack the cancer. It works by making the cancer cells more visible to your immune system. This encourages the immune system to then attack the cancer. Treatment with peginterferon alfa 2a helps to reduce the size of your and reduce the number of the produces.
Find out more about how immunotherapy works
You have peginterferon alfa 2a as an injection just under the skin (subcutaneously). Peginterferon alfa 2a comes as a pre filled syringe.
A nurse will teach you to give the injection yourself at home. Or a family member can learn how to do it.
You need to keep your peginterferon alfa 2a in the fridge in its container to protect it from the light.
You usually have injections under the skin into the stomach or thigh.
You might have stinging or a dull ache for a short time after this type of injection, but it doesn’t usually hurt much. The skin in the area may go red and itchy for a while.
The video below shows you how to inject just under your skin (subcutaneously). It lasts just over 3 minutes.
You usually have peginterferon alfa 2a once a week. This might be reduced to every 2 or 3 weeks depending on your blood test results. You continue to have peginterferon alfa 2a for as long as it is working and you are not experiencing too many side effects.
You have blood tests before and during your treatment. They check your levels of and other substances in the blood. They also check how well your liver and kidneys are working.
Before treatment starts you may have a blood test to check for viruses such as hepatitis B, hepatitis C, and HIV. This is called a viral screen.
It’s important for your doctor to know if you have had any of these viruses. This is because this treatment can weaken your and can cause the virus to become active again (reactivation).
You also have an eye test before you start treatment.
Side effects can vary from person to person. They also depend on what other treatments you're having.
Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:
you have severe side effects
your side effects aren’t getting any better
your side effects are getting worse
Early treatment can help manage side effects better.
We haven't listed all the side effects here. Talk to your healthcare team if you have any new symptoms that you think might be a side effect of your treatment.
Remember it is very unlikely that you will have all of these side effects. But you might have some of them at the same time.
These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:
If you have difficulty sleeping, it can help to change a few things about how you try to sleep. Try to go to bed and get up at the same time each day and spend some time relaxing before you go to bed. Some light exercise each day may also help.
You might have a change in your mood and mental health. This treatment commonly causes a feeling of anxiety, irritability and a very low mood (depressed).
Some people may be more aggressive, nervous and you may feel your emotions and mood are very up and down. These side effects are less common.
Rarely this treatment can cause suicidal thoughts, hearing voices or seeing things that aren’t there (hallucinations).
This treatment can cause headaches. It can also cause a severe headache, called a migraine, but this happens less often.
Tell your doctor or nurse so they can give you painkillers to help.
It is common with this treatment to find it difficult to think clearly or concentrate. You might find your memory is worse than before you had this medicine, but this happens less often. Let your nurse or doctor know if you have this.
You might feel sick but this is usually mild. Less often peginterferon alpha 2a can make you be sick.
Tell your healthcare team if you feel sick, they can give you anti sickness tablets to help if you need them.
This treatment causes pain and cramps in different areas of the body. The most common sites are your muscles, joints and tummy (abdomen).
Less commonly, you might get pain in your back, neck, chest, bones, ligaments, tendons and nerves.
This treatment can also cause arthritis.
Contact your advice line if you are in pain. Depending on what is causing the pain, they might give you medicine to help.
Contact your advice line if you have diarrhoea. For example, in one day you have 2 or more loose bowel movements than usual. If you have a , you might have more output than normal. Your doctor may give you anti diarrhoea medicine to take home with you after treatment.
Try to eat small meals and snacks regularly. It’s best to try to have a healthy balanced diet if you can. You don’t necessarily need to stop eating foods that contain . But if your diet is normally very high in fibre, it might help to cut back on high fibre foods such as beans, nuts, seeds, dried fruit, bran and raw vegetables.
Drink plenty to try and replace the fluid lost. Aim for 8 to 10 glasses per day.
Your hair may thin but you’re unlikely to lose all your hair. It is almost always temporary and your hair will grow back when you finish your treatment.
You might notice redness, swelling and pain around the area where you have had the injection.
You might feel very tired and as though you lack energy.
Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.
You might lose your appetite for various reasons while having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.
You may get a cough or feel short of breath with this treatment. Less commonly you may feel short of breath with physical activity.
Rarely peginterferon alpha 2 can cause other changes to your breathing such as a wheeze or changes to the lung tissue, making it less flexible.
This drug might make you feel dizzy. Don’t drive or operate machinery if you have this.
You might get a high temperature. Or you might feel cold or start shivering (chills).
Skin problems include a skin rash, itching, swelling, dry skin and inflammation.
Less commonly this treatment can cause psoriasis. This causes a build up of skin cells to form thick, flaky, scaly patches (plaques). Your skin might develop a raised, red, itchy skin rash (urticaria). Your skin might also be more sensitive to light.
Rarely you may get a severe skin reaction that may start as tender red patches which leads to peeling or blistering of the skin. You might also feel feverish, and your eyes may be more sensitive to light. This is serious and could be life threatening.
Let your doctor, nurse or pharmacist know of any skin changes. They can let you know what you can use to help.
These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:
swollen
fluid build up of the hands, legs or feet (oedema)
changes to sensation of touch, pain or temperature. You might have a tingling, pricking, burning or numbing sensation. Or your body may feel normal sensations more strongly
tremor or shaking hands
reddening (flushing) of the skin
taste changes
earache, rarely you may develop hearing loss
heart changes such as racing, fluttering, pounding or a fast heartbeat. Rarely you might have other including a and . Symptoms include breathlessness, feeling tired, chest pain, swelling of the ankles or legs and an irregular heart rhythm
dry, sore mouth and ulcers
hot flushes, sweating more than usual, you might also have drenching night sweats
difficulty getting an (impotence)
nightmares
feeling very sleepy, drowsy or finding it difficult to wake up. Very rarely this can cause you to be unconscious and not wake (coma)
breathlessness and looking pale due to a drop in (anaemia)
bruising, bleeding, small red spots (petechia), nose bleeds or bleeding gums due to a drop in
changes to the level of hormones the makes. If low this can cause tiredness, feeling cold, weight gain, feeling sad or depressed. If high this can cause weight loss, a fast heartbeat and anxiety. Rarely you might have of the thyroid
infections affecting the nose, throat, airways to the lungs, or mouth. Rarely you might get an infection of the skin
eye problems such as pain, blurred vision, inflammation and severe dry eyes because of low vitamin A. Rarely you might have bleeding in the eye
less interest in sex (libido)
fainting
flu-like symptoms - symptoms can include headaches, aching muscles, a high temperature, stuffy nose and sinuses, sore throat or runny nose
the feeling of the room spinning or moving around you (vertigo)
heartburn, bloating and burping
difficulty swallowing
generally feeling unwell
passing more wind than usual
feeling very thirsty
weight loss
These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:
clumping of cells to make small lumps in your body, often in the lungs (sarcoidosis)
a low level of fluid in the body (dehydration)
, more rarely you might develop a life threatening problem where the lack of insulin causes harmful substances to build up in the blood
bleeding from the . Contact your healthcare team if you have any abnormal bleeding
high blood pressure - symptoms can include blurred vision, nosebleeds, dizziness, headaches, shortness of breath and chest pain
changes to how your liver works and liver cancer, more rarely your liver may stop working. Symptoms of liver problems can include yellowing of the skin or eyes, feeling or being sick, bleeding or bruising, dark urine, and stomach pain
pins and needles in your arms and legs
a severe allergic reaction that can cause a rash, shortness of breath, redness or swelling of the face and dizziness. Tell your nurse if you notice any of these symptoms or dial 999
seizures (fits)
blood clots that can be life threatening; signs are pain, redness and swelling where the clot is. Feeling breathless can be a sign of a blood clot in the lung. Contact your advice line or doctor straight away if you have any of these symptoms
bleed on the brain – symptoms include a sudden severe headache, weakness on one side of the body, being sick, slurred speech and feeling confused
inflammation of your blood vessels – symptoms can vary depending on which blood vessels are affected - general symptoms include feeling very tired, loss of appetite, weight loss, a high temperature, and aches and pains
inflammation of your pancreas – symptoms include severe tummy pain, feeling or being sick, a high temperature or you may have loose poo
lupus, this is a long term condition that causes joint pain and swelling, skin rashes, feeling very tired, and swelling of the feet
We have more information about side effects and tips on how to cope with them.
Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.
Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.
It is not known whether this treatment affects in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.
It is unknown whether treatment may or may not harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you are having treatment. Let your team know straight away if you or your partner become pregnant while having treatment.
Talk to your doctor or nurse about effective contraception you can use during treatment. Ask how long you should use it before starting treatment and after treatment has finished.
It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.
If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.
Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having.
Ask your doctor or pharmacist how long you should avoid live vaccinations.
In the UK, live vaccines include rubella, mumps, measles, BCG, and yellow fever.
You can usually have:
other vaccines, but they might not give you as much protection as usual
the flu vaccine (as an injection)
the coronavirus (COVID-19) vaccine
Talk to your doctor or pharmacist about the best time to have a vaccine in relation to your cancer treatment.
You can be in contact with other people who have had live vaccines as injections. If someone has had a live vaccine by mouth or nasal spray there may be a small risk the vaccine virus can be passed onto you if your is weakened.
Your healthcare team will let you know if you need to take any precautions if you are in close contact with someone who has had a live vaccine.
For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.
You can report any side effect you have to the Medicines and Healthcare products Regulatory Agency (MHRA) as part of their Yellow Card Scheme.
Last reviewed: 04 Jun 2026
Next review due: 04 Jun 2029
Myeloproliferative neoplasms are a group of rare disorders of the bone marrow that cause an increase in the number of blood cells.
Immunotherapy uses our immune system to fight cancer. It works by helping the immune system recognise and attack cancer cells.
Cancer drugs have side effects and these can vary from person to person. But there are things that you can do to help you cope.
Coping with cancer can be difficult. There is help and support available. Find out about the emotional, physical and practical effects of cancer and how to manage them.
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