Mercaptopurine (Xaluprine)

Mercaptopurine is also called Xaluprine. It is a chemotherapy drug used to treat some types of leukaemia Open a glossary item

You might also have as part of a clinical trial.

Find out more about your cancer type

How does mercaptopurine work?

Mercaptopurine is one of a group of chemotherapy drugs known as anti metabolites. These drugs stop cells making and repairing DNA. Cancer cells need to make and repair DNA Open a glossary item so that they can grow and multiply. 

How do you have mercaptopurine?

Mercaptopurine comes as pale yellow tablets and as a pink to brown liquid (oral suspension). The liquid medicine is called Xaluprine. 

Taking mercaptopurine tablets

You swallow the tablets whole with lots of water. You can take them with food, or on an empty stomach. You should continue taking the tablets the way you started that is either with food or on an empty stomach.

You should take the tablets at the same time in the evening.

You must take tablets according to the instructions your doctor or pharmacist gives you.

You should take the right dose, not more or less.

Talk to your specialist or advice line before you stop taking a cancer drug.

Taking mercaptopurine liquid

Your nurse or pharmacist will show you how to measure the dose of liquid mercaptopurine using a syringe. You wear disposable gloves while doing this so that the drug doesn't come into contact with your skin.

You take mercaptopurine in the evening, with food or on an empty stomach. But whichever you choose, you should do the same thing each day. You should drink some water after taking the liquid.

You should not take the tablets or liquid at the same time as milk or dairy products. You can take them:

  • 1 hour before milk or dairy products
  • 2 hours after milk or dairy products

If you take too much mercaptopurine

If you accidentally take more mercaptopurine than you should you might feel sick, be sick or have diarrhoea. 

Tell your doctor or go to a hospital straight away. Take the medicine pack with you.

If you forget to take mercaptopurine

Don't take a double dose to make up for the dose that you forgot. Tell your doctor or nurse. 

How often do you have mercaptopurine?

You usually have mercaptopurine as a course of several cycles of treatment Open a glossary item. The treatment plan for mercaptopurine depends on which type of cancer you have. 

Your doctor, nurse or pharmacist will tell you how often you should take mercaptopurine for. 


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 and kidneys are working.

Side effects

Side effects can vary from person to person. They also depend on what other treatments you're having. 

When to contact your team

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. 

Contact your advice line immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. 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.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Increased risk of getting an infection

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 

Bruising, bleeding gums or nosebleeds

This is due to a drop in the number of platelets in your blood. These blood cells help the blood to clot when we cut ourselves. You may have nosebleeds or bleeding gums after brushing your teeth. Or you may have lots of tiny red spots or bruises on your arms or legs (known as petechiae).

Occasional side effects

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:

  • diarrhoea
  • feeling or being sick
  • breathlessness and looking pale (due to low red blood cell counts) and tiredness
  • sore mouth
  • changes to how your liver works. It can also cause the death of liver cells.
  • blocked bile ducts

Rare side effects

This side effects happens in fewer than 1 in 100 people (fewer than 1%). You might have one or more of them. They include:

  • loss of appetite
  • skin rash
  • inflammation of the pancreas, symptoms include severe tummy pain, feeling or being sick, a high temperature or you may have loose poo
  • aching muscles
  • high temperature
  • risk of developing another cancer
  • allergic reaction

Other side effects

There isn't enough information to work out how often this side effect happens.

Mercaptopurine can make your skin sensitive to sunlight or UV light.

Don’t use sunbeds or sit in the sun. Cover up or use a sunscreen if you go out in the sun. Remember to put sun cream on your head or wear a hat if you have lost any hair there.

Find out more about sun safety

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do I need to know?

Other medicines, foods and drink

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Lactose and mercaptopurine 

This drug contains lactose (milk sugar). If you have an intolerance to lactose, contact your doctor before taking this medicine.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you are having treatment with this drug and for at least 3 months afterwards.

Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner become pregnant while having treatment.


It is not known whether this treatment affects fertility Open a glossary item in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.


Don’t breastfeed during this treatment because the drug may come through into your breast milk.

Treatment for other conditions

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, yellow fever and one of the shingles vaccines called Zostavax.

You can 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 it in relation to your cancer treatment

Members of your household who are aged 5 years or over are also able to have the COVID-19 vaccine. This is to help lower your risk of getting COVID-19 while having cancer treatment and until your immune system Open a glossary item recovers from treatment.

Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine. Sometimes people who have had the live shingles vaccine can get a shingles type rash. If this happens they should keep the area covered.

If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray as this is a live vaccine. This is for 2 weeks following their vaccination.

Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.

More information about this treatment

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 Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

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