What is mercaptopurine?

Mercaptopurine is a chemotherapy drug mainly used to treat acute lymphoblastic leukaemia (ALL). It can also be used to treat acute myeloid leukaemia (AML) and acute promyelocytic leukaemia (a rare form of AML).

It may sometimes be used to treat other cancers. It is best to read this information with our general information about chemotherapy and the type of cancer you have.

Your doctor will talk to you about this treatment and its possible side effects before you agree (consent) to treatment.

How mercaptopurine is given

During treatment you usually see a blood cancer doctor (haematologist), a chemotherapy nurse or a specialist nurse, and a specialist pharmacist. This is who we mean when we mention doctor, nurse or pharmacist in this information.

Before or on the day of treatment, a nurse or person trained to take blood (phlebotomist) will take a blood sample from you. This is to check that your blood cells are at a safe level for you to have chemotherapy. 

You will see a doctor or nurse before you have chemotherapy. They will talk to you about your blood results and ask you how you have been feeling. If your blood results are okay, the pharmacist will prepare your chemotherapy. Your nurse will tell you when your treatment is likely to be ready. 

Your course of chemotherapy

Mercaptopurine comes in tablets, so you can take it at home. It also comes as a liquid (suspension) called Xaluprine®. Mercaptopurine may be given on its own, or with other chemotherapy drugs.

Chemotherapy is usually given as a course of several cycles of treatment over a few months. Your nurse or doctor will discuss your treatment plan with you. They may give you a copy of the treatment plan to take home with you. 

The nurse or pharmacist will give you the tablets or liquid to take home. Always take them exactly as explained. This is important to make sure they work as well as possible for you. 

Your nurse or pharmacist may also give you anti-sickness drugs and other medicines to take home. Take all your medicines exactly as they have been explained to you.

Taking mercaptopurine

You can take mercaptopurine with food or on an empty stomach. Take it in the same way and at the same time every day. If you are taking the liquid form (Xaluprine®), it is important to take it in the evening. 

You should not take mercaptopurine tablets or liquid with milk or dairy products. Take it:

  • at least 1 hour before having milk or dairy products
  • at least 2 hours after having milk or dairy products.  

The tablets must be swallowed whole with a glass of water. They should not be chewed, broken or crushed. 

If you are taking Xaluprine® liquid, your nurse or pharmacist will show you how to take it. You will use plastic syringes to measure the dose. It is important to follow your nurse or pharmacist’s advice. You need to wear disposable gloves to protect your skin when handling the liquid. Close the lid of the bottle tightly when you have finished. You should have a drink of water after taking the liquid.

If you forget to take the tablets or liquid, tell your doctor. Do not take a double dose. 

Other things to remember about your tablets or liquid:

  • Wash your hands after taking your tablets or liquid. 
  • Other people should avoid direct contact with the chemotherapy drugs. 
  • Keep them in the original package and at room temperature, away from heat and direct sunlight.
  • Keep them safe and out of sight and reach of children.
  • If you are sick just after taking the tablets or liquid, contact the hospital. Do not take another dose.
  • If your treatment is stopped, return any unused tablets or liquid to the pharmacist. 

About side effects

We explain the most common side effects of this treatment here. We also include some less common side effects.

You may get some of the side effects we mention, but you are unlikely to get all of them. If you are also having treatment with other cancer drugs, you may have some side effects that we have not listed here. Always tell your doctor, nurse or pharmacist about any side effects you have.

Your doctor can give you drugs to help control some side effects. It is important to take them exactly as your nurse or pharmacist explains. This means they will be more likely to work for you. Your nurse will give you advice about managing your side effects. After your treatment is over, most side effects start to improve.

Serious and life-threatening side effects

Some cancer treatments can cause severe side effects. Rarely, these may be life-threatening. Your cancer doctor or nurse can explain the risk of these side effects to you.

Contact the hospital

Your nurse will give you telephone numbers for the hospital. If you feel unwell or need advice, you can call them at any time of the day or night. Save these numbers in your phone or keep them somewhere safe.

More information

We cannot list every side effect for this treatment. There are some rare side effects that are not listed. You can visit the electronic Medicines Compendium (eMC) for more detailed information.

Common side effects

Risk of infection

This treatment can reduce the number of white blood cells in your blood. These cells fight infection. If the number of white blood cells is low, you are more likely to get an infection. A low white blood cell count is sometimes called neutropenia.

An infection can be very serious when the number of white blood cells is low. It is important to get any infection treated as soon as possible. Contact the hospital straight away on the 24-hour contact number you have been given if:

  • your temperature goes over 37.5°C (99.5°F)
  • you suddenly feel unwell, even with a normal temperature
  • you have symptoms of an infection
  • your temperature goes below 36°C (96.8°F).

Symptoms of an infection include:

  • feeling shivery and shaking
  • a sore throat
  • a cough
  • breathlessness
  • diarrhoea
  • needing to pass urine (pee) a lot, or discomfort when you pass urine.

It is important to follow any specific advice your cancer treatment team gives you.

You will have regular blood tests during treatment. If needed, your doctor may reduce or delay your treatment for a short time, until your cell count increases.

Bruising and bleeding

This treatment can reduce the number of platelets in your blood. Platelets are cells that help the blood to clot.

If the number of platelets is low, you may bruise or bleed easily. You may have:

  • nosebleeds
  • bleeding gums
  • heavy periods
  • blood in your urine (pee) or stools (poo)
  • tiny red or purple spots on the skin that may look like a rash.

Tell your doctor if you have any unexplained bruising or bleeding. You may need a drip to give you extra platelets. This is called a platelet transfusion.

Anaemia (low number of red blood cells)

This treatment can reduce the number of red blood cells in your blood. Red blood cells carry oxygen around the body. If the number of red blood cells is low, this is called anaemia. You may have symptoms such as:

  • pale skin
  • lack of energy
  • feeling breathless
  • feeling dizzy and light-headed.

Tell your doctor or nurse if you have these symptoms.

If you are very anaemic, you may need a drip to give you extra red blood cells. This is called a blood transfusion.

Feeling sick

Your doctor will give you anti-sickness drugs to help prevent or control sickness during your treatment. Take the drugs exactly as your nurse or pharmacist tells you. It is easier to prevent sickness than to treat it after it has started.

If you feel sick, take small sips of fluids often and eat small amounts regularly. It is important to drink enough fluids. If you continue to feel sick, or are sick (vomit) more than once in 24 hours, contact the hospital as soon as possible. They will give you advice. Your doctor or nurse may change the anti-sickness drug to one that works better for you.

Loss of appetite

This treatment can affect your appetite. Do not worry if you do not eat much for a day or two. But if your appetite does not come back after a few days, tell your nurse or dietitian. They will give you advice. They may give you food or drink supplements.

Sore mouth and throat

This treatment may cause a sore mouth and throat. You may also get mouth ulcers. This can make you more likely to get a mouth or throat infection. Use a soft toothbrush to clean your teeth or dentures in the morning, at night and after meals.

If your mouth or throat is sore:

  • tell your nurse or doctor – they can give you a mouthwash or medicines to help
  • try to drink plenty of fluids
  • avoid alcohol, tobacco and foods that irritate your mouth and throat.

Diarrhoea

This treatment may cause diarrhoea. Diarrhoea means passing more stools (poo) than is usual for you, or having watery or loose stools. If you have a stoma, it will be more active than usual.

If you have diarrhoea:

  • try to drink at least 2 litres (3½ pints) of fluids each day
  • avoid alcohol, caffeine, milk products, high-fat foods and high-fibre foods
  • contact the hospital for advice.

Changes in the way the liver works

This drug may cause changes in the way your liver works. These will usually go back to normal after treatment finishes.

The drug may cause your skin and the whites of your eyes to become yellow (jaundice). Tell your nurse or doctor if you notice this. You will have regular blood tests to check how well your liver is working.

Less common side effects of mercaptopurine

Swollen pancreas (pancreatitis)

Mercaptopurine can make your pancreas swell (pancreatitis). This side effect is rare. Tell your doctor straight away if:

  • you get sharp pain in the upper tummy (abdomen) and
  • you are sick or vomit.

The doctor will examine your tummy. They will give you drugs to help the symptoms. The doctor will give you any other treatment you need.

Hair loss

Your hair may get thinner but you are unlikely to lose all the hair from your head. Hair loss is almost always temporary and your hair will usually grow back after treatment ends. Your nurse can talk to you about ways to cope with hair loss.

Allergic reaction

Mercaptopurine can cause an allergic reaction. This side effect is rare. Signs of a reaction can include:

  • a rash
  • feeling itchy
  • joint pain
  • swelling of your face or mouth and throat
  • feeling unwell.

Tell your nurse straight away if you have any of these symptoms. Contact the hospital immediately if you develop any of these symptoms after you get home. You should contact the hospital on the number they gave you or visit the nearest accident and emergency department.

Sensitivity to sun

During treatment and for several months afterwards, you will be more sensitive to the sun and your skin may burn more easily than usual. You can still go out in the sun but cover up with clothing and a hat. You should use a suncream with a sun protection factor (SPF) of at least 30.

Other information

Blood clot risk

Cancer and some cancer treatments can increase the risk of a blood clot. Symptoms of a blood clot include:

  • throbbing pain, redness or swelling in a leg or arm
  • suddenly feeling breathless or coughing
  • sharp chest pain, which may be worse when you cough or take a deep breath.

If you have any of these symptoms, contact the hospital straight away on the 24-hour contact number you have been given. If you cannot get through to your doctor, call the NHS urgent advice number on 111.

A blood clot is serious, but it can be treated with drugs that thin the blood (anticoagulants). Your doctor or nurse can give you more information.

You can help reduce the risk of developing a blood clot by:

  • staying active during treatment
  • drinking plenty of fluids, especially water.

You may be given anticoagulants to help prevent a clot.

Other medicines

Some medicines can affect how this treatment works or be harmful when you are having it. Always tell your cancer doctor about any drugs you are taking or planning to take, such as:

  • medicines you have been prescribed
  • medicines you buy in a shop or chemist
  • vitamins, herbal drugs and complementary therapies.

Tell other doctors, pharmacists or dentists who prescribe or give you medicines that you are having this cancer treatment.

You can visit the electronic Medicines Compendium (eMC) for more detailed information about your treatment.

Lactose

Mercaptopurine contains a small amount of lactose. Talk to your doctor if you have a lactose intolerance. You must do this before taking mercaptopurine.

Vaccinations

Vaccinations can reduce your risk of getting certain infections. Your doctor or nurse may talk to you about having vaccinations.

Doctors usually recommend that people with cancer have a flu vaccination and a coronavirus vaccination. These are both inactivated vaccinations that can help reduce the risk of infection. People with weak immune systems can have these, as they are not live vaccinations.

If your immune system is weak, you need to avoid live vaccinations. This is because they can make you unwell. Live vaccines, such as shingles, contain a very weak version of the illness they are vaccinating you against. Your cancer doctor or GP can tell you more about live and inactivated vaccinations.

Contraception

Your doctor will advise you not to get pregnant or make someone pregnant while having this treatment. The drugs may harm a developing baby. It is important to use contraception during your treatment and for a while after treatment finishes. Your doctor, nurse or pharmacist can tell you more about this.

Breastfeeding

You are advised not to breastfeed while having this treatment, or for some time after treatment finishes. This is because the drugs could be passed to the baby through breast milk.

Your doctor or nurse can give you more information.

Fertility

Some cancer drugs can affect whether you can get pregnant or make someone pregnant. If you are worried about this, it is important to talk with your doctor before you start treatment.

Sex

If you have sex during a course of this treatment, you should use barrier protection such as a condom or dental dam. This will protect your partner if any of the drug is in your semen or vaginal fluid.

Medical and dental treatment

If you need medical treatment for any reason other than cancer, always tell the doctors and nurses you are having cancer treatment. Give them the contact details for your cancer doctor so they can ask for advice.

If you think you need dental treatment, talk to your cancer doctor or nurse. Always tell your dentist you are having cancer treatment.

About our information


  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert health professionals and people living with cancer.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.