Cancer drugs A to Z list
Pembrolizumab is a type of called a checkpoint inhibitor. Immunotherapy stimulates the body's to fight cancer cells.
Cancer cells can make proteins that stop our immune system from attacking them. Immune checkpoint inhibitors block these proteins.
Pembrolizumab targets and blocks a protein called PD-1 on the surface of certain immune cells called . Blocking PD-1 triggers the T cells to find and kill cancer cells.
Find out more about checkpoint inhibitors
You can have pembrolizumab as a drip into your bloodstream (intravenously). Or as an injection under your skin (subcutaneous injection).
Your doctor can switch the way you have treatment. So you may change from having it into your bloodstream to having it as an injection under the skin. Your doctor will talk with you about this and explain the change if it is suitable for you.
You might have treatment through a long plastic tube that goes into a large vein in your chest. The tube stays in place throughout the course of treatment. This can be a:
central line
PICC line
portacath
You might have treatment through a thin short tube (a cannula) that goes into a vein in your arm. You have a new cannula each time you have treatment.
You have pembrolizumab as a subcutaneous injection in your tummy (abdomen) or thigh.
You might have stinging or a dull ache for a short time after this type of injection, but they don't usually hurt much. The skin in the area may go red and itchy for a while.
Read more about having cancer drugs as an injection or drip
You have pembrolizumab in . This means you have the pembrolizumab and then a rest to allow your body to recover. A treatment cycle is every 3 or 6 weeks.
If you have pembrolizumab into your bloodstream, it takes about 30 minutes each time you have it. If you have it as an injection under your skin, your nurse gives it to you over 1 to 2 minutes.
How long you continue pembrolizumab for depends on the of the cancer.
You might have pembrolizumab on its own or with other cancer treatments. This depends on the type of cancer.
If you are having surgery, you might have pembrolizumab before (neoadjuvant) or after (adjuvant) your operation. Or you might have both.
You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver, kidneys and 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).
Depending on the cancer type, your doctor may also check for certain changes or a protein called PD-L1 on the surface of cancer cells. To test your cancer cells, doctors need a sample of your cancer. They might be able to use a sample from a biopsy or operation you have already had.
Side effects can vary from person to person. They also depend on what other treatment you are having.
Your doctor, pharmacist or nurse will go through the possible side effects. They will monitor you closely 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:
You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.
You may also be breathless and have a cough. Occasionally this could be due to an infection (pneumonia) or inflammation of the lungs (pneumonitis). Let your doctor or nurse know straight away if you become breathless, develop a cough or chest pain.
You might feel very tired and as though you lack energy. There are many causes of tiredness but sometimes it is due to changes in the thyroid or . Tell your healthcare team if you become very tired.
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.
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.
Occasionally, diarrhoea can be caused by inflammation of bowel (colitis) which can be very serious. This can also cause tummy pain or diarrhoea at night. You might also have watery poo or blood or mucus in your poo. You might need treatment with steroids or other medicines.
Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also help.
It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treat it once it has started.
You might notice skin changes, such as itching and rashes.
Occasionally your skin may become dry. You can get redness, bumps or lighter patches on your skin. Or you might get a rash similar to acne on your front and back.
Rarely you might get redness or a darker rash that covers large parts of your body and the skin may go scaly and peel. You might also get blisters on your skin or in areas like the inside of your mouth. Or sores in the folds of your skin. This can include areas such as in your groin or armpits.
Other rare skin changes include 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.
Skin changes are usually mild but can become more serious if they are not treated. Your doctor might give you creams, steroids or other medicines to help.
The level of your thyroid hormones may drop, this is called hypothyroidism. You may feel tired, cold, gain weight, feel sad or depressed, or your voice may deepen. You will have regular blood tests to check your thyroid hormone levels.
If your thyroid hormone levels are low, your team may prescribe medicine to replace them. You normally take this for the rest of your life.
Occasionally, you can get high thyroid hormone levels. Symptoms include anxiety, difficulty sleeping and weight loss.
You might lose your appetite for various reasons while having cancer treatment. Sickness, taste changes or tiredness can put you off food and drinks.
Tell your healthcare team if you keep getting headaches. They can give you painkillers to help.
is easier to sort out if you treat it early. Drink plenty and eat as much fresh fruit and vegetables as you can. Try to take gentle exercise, such as walking. Tell your healthcare team if you think you are constipated. They can give you a laxative if needed.
You might feel pain from your tummy (abdomen), muscles and joints.
Occasionally you may get pain in your arms and legs, swelling in your joints (arthritis) or inflammation of the muscles causing weakness and pain
Speak to your doctor or nurse about what painkillers you can take to help with this.
You may have swelling of your face, hands and legs due to a build up of fluid (oedema).
Tell your healthcare team straightaway if you get a high temperature. Ask them if you can take paracetamol to help lower your temperature.
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:
a drop in the number of and in your body which may increase your risk of infection and cause bruising and bleeding
an allergic reaction during treatment. This can cause a rash, shortness of breath, redness or swelling of the face and dizziness. Some allergic reactions can be life threatening, alert your nurse or doctor if you notice any of these symptoms
inflammation of the adrenal glands - this can cause a drop in the level of a hormone called cortisol. Symptoms include feeling tired, sick or dizzy. You may need treatment with steroids. If your adrenal glands stop working, you can feel very ill and need medical attention
high levels of creatinine - this shows how well your kidneys are working. Rarely, you can get inflammation of the kidneys. You have regular blood tests to check this
low levels of minerals and salts in your body such as sodium, potassium and calcium. Less often you might get high levels of calcium – you have regular blood tests to check these
difficulty sleeping
dizziness
taste changes
numbness or tingling in your hands and feet
dry eyes
dry mouth
heart changes such as an abnormal heart rhythm
high blood pressure
hair loss or rarely changes in hair colour
chills and flu-like symptoms
inflammation of the liver (hepatitis) - this is usually picked up on a blood test before you have any symptoms. If you do get symptoms, they can include tummy pain, feeling or being sick, tiredness and weakness, loss of appetite, yellowing of the skin or whites of the eyes, or dark coloured pee
These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:
breakdown of in your body which can cause yellowing of the skin and eyes, dark coloured urine and high temperature (fever)
a condition where cells in your body clump together to make lumps. This usually affects your lungs and skin
inflammation of the – symptoms can include fatigue, feeling generally weak, joint pain, vision problems and headaches
inflammation in the heart (myocarditis) or the lining that covers the heart (pericarditis) – symptoms include chest pain or tightness, shortness of breath even when resting, a high temperature, tiredness and feeling generally unwell
fluid build up around your heart
stomach inflammation (gastritis) – this can cause tummy pain, indigestion, feeling or being sick, feeling full or like you need to burp or pass wind
bladder inflammation – doctors call this cystitis. You may get pain when peeing, peeing more often, blood in your pee or tummy pain
inflammation of the pancreas (pancreatitis) – symptoms include severe tummy pain, feeling or being sick, a high temperature, and loose poo
inflammation in the brain (encephalitis) or the tissues covering the brain and spinal cord (meningitis) – these can cause confusion, a high temperature, headaches, neck stiffness, feeling or being sick, sensitivity to light or seizures (fits)
inflammation of the blood vessels (vasculitis)
a condition where the immune system becomes overactive and causes severe inflammation. Symptoms include a high temperature, low blood cell counts and damage to tissues and organs
inflammation of the heart, muscles and nerves that happens at the same time. Sometimes the liver may also become inflamed
sores (ulcers) in the stomach or bowels
high levels of glucose in your body (diabetes) which needs to be treated with
the immune system attacking the nervous system (Guillain-Barre syndrome) - causes numbness, weakness and pain in the body. Go to A&E if you have any numbness or are unable to move
severe muscle weakness that worsens with physical exercise
inflammation of the eye causing dry eyes, changes in your vision or sensitivity to light
a condition that affects the glands that make moisture for the body, such as tears and saliva (Sjogren's syndrome)
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.
This drug may harm a baby developing in the womb. It is important for women not to become pregnant while they are having treatment and for 4 months afterwards.
Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you become pregnant while you're having treatment.
Don’t breastfeed during this treatment because the drug may come through into your breast milk.
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: 24 Mar 2026
Next review due: 24 Mar 2029
Immunotherapy uses our immune system to fight cancer. It works by helping the immune system recognise and attack cancer cells.
Search for the cancer type you want to find out about. Each section has detailed information about symptoms, diagnosis, treatment, research and coping with cancer.
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.
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.
There are many cancer drugs, cancer drug combinations and they have individual side effects.
About Cancer generously supported by Dangoor Education since 2010. Learn more about Dangoor Education
Search our clinical trials database for all cancer trials and studies recruiting in the UK.
Connect with other people affected by cancer and share your experiences.
Questions about cancer? Call freephone 0808 800 40 40 from 9 to 5 - Monday to Friday. Alternatively, you can email us.
