Mercaptopurine (Xaluprine) | Cancer Research UK
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What mercaptopurine is

Mercaptopurine is a chemotherapy drug used to treat some types of leukaemia.


How mercaptopurine works

It 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 so that they can grow and multiply.


How you have mercaptopurine

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

It is very important that you take the medicine according to the instructions your doctor or pharmacist gave you. For example, whether you have a full or empty stomach can affect how much of a drug gets into your bloodstream. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

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

Taking mercaptopurine tablets

You swallow the tablets whole with lots of water. If you need to break them in half, wash your hands afterwards. Make sure that you don't breathe in any of the powder released by the tablet. You should take the tablets at the same time each day, at least 1 hour before or 3 hours after food or milk. 

Taking mercaptopurine liquid

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

You take the Xaluprine in the evening. You can take it with food or on an empty stomach. But whichever you choose, you should do the same thing each day. Milk or dairy products can make the medicine less effective so you should take Xaluprine at least 1 hour before or 2 hours after milk or dairy products.

If you take too much mercaptopurine

If you accidentally take more mercaptopurine than you should, tell your doctor or go to a hospital straight away. You may feel sick, be sick or have diarrhoea. Take the medicine pack with you.

If you forget to take mercaptopurine

If you forget to take a dose of mercaptopurine tell your doctor. Don't take a double dose to make up for the dose that you forgot.


Tests during treatment

You have blood tests before starting treatment and regularly during your treatment. The tests check your levels of blood cells. They also check how well your liver and kidneys are working.


About side effects

We've listed the side effects associated with mercaptopurine. You can use the links to find out more about each side effect. Where there is no link, please go to our information about cancer drug side effects or use the search box at the top of the page.

You may have a few side effects. They 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)

The side effects may be different if you are having mercaptopurine with other medicines.

Tell your doctor, nurse or pharmacist straight away if any of the side effects get severe.


Common side effects

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

  • 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, a sore throat, pain passing urine, or you may feel cold and shivery. If you have a severe infection this can be life threatening. Contact your treatment centre straight away if you have any of these side effects or if your temperature goes above 38°C
  • Bruising more easily due to a drop in platelets – 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)
  • Tiredness and weakness (fatigue) during and after treatment – most people find their energy levels are back to normal within 6 months to a year

Occasional side effects

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

  • Diarrhoea – drink plenty of fluids and tell your doctor or nurse if diarrhoea becomes severe, or continues for more than 3 days
  • Feeling or being sick is usually well controlled with anti sickness medicines
  • A sore mouth and throat
  • Liver changes that are very mild and unlikely to cause symptoms – the liver will almost certainly go back to normal when treatment ends
  • Loss of fertility – you may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future. Men may be able to store sperm before starting treatment
  • Breathlessness and looking pale due to a drop in red blood cells (anaemia) – you may need a blood transfusion
  • Women may stop having periods (amenorrhoea) but this may only be temporary
  • An itchy rash
  • Headaches
  • Loss of appetite
  • High uric acid levels in your blood due to cancer cells being broken down by the body (tumour lysis syndrome). You will have regular blood tests and will be asked to drink plenty of fluids to flush out the uric acid. Your doctor or nurse may give you medicines to control this

Rare side effects

Fewer than 1 in 100 people have these.

  • Hair loss – this is rare, but can begin 2 to 5 weeks after treatment starts
  • Reddening of the skin in areas where you have had radiotherapy in the past. The skin may also get dry and flaky and feel sore and hot. This goes away on its own but keep affected areas out of the sun
  • A high temperature (fever) and chills
  • An inflamed pancreaslet your doctor or nurse know straight away if you have sudden, severe pain in your upper chest
  • Joint pains – your doctor or nurse can give you painkillers to help

Important points to remember

Talk to your doctor, pharmacist or nurse about all your side effects so 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.

Other medicines

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

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child 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.


Don't breastfeed during this treatment because the drug may come through in the breast milk.

Other conditions

Mercaptopurine may cause very severe side effects if you have a condition where your body produces too little of something called TPMT (thiopurine methyltransferase). Your doctor may do blood tests to check the levels before you start treatment.

Lactose and mercaptopurine

Mercaptopurine tablets contain lactose (milk sugar). If you have an intolerance to lactose, contact your doctor before taking this medicine.


Immunisations and chemotherapy

You shouldn't have immunisations with live vaccines while you are having chemotherapy 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 chemotherapy. 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 mercaptopurine

This page doesn't list all the very rare side effects of this treatment 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: 27 January 2016