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NZ Formulary

Mercaptopurine (for inflammatory conditions)

mer-kap-toe-pure-een

What does it do?

Mercaptopurine is an immunosuppressant medicine used to treat inflammatory bowel disease, such as Crohn’s disease. It calms down your overactive immune system that causes inflammation in your bowel. It is also used for other conditions.

Before you start

  • Tell your doctor if you have kidney or liver problems, or if you have taken immunosuppressant medicines in the past.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
  • You will need a blood test to check if mercaptopurine is suitable for you.
  • Mercaptopurine weakens your immune system, making it harder for your body to fight infections. You may need tests before you start to make sure you don't have any infections like tuberculosis (TB), HIV, or hepatitis B and C.
  • Ask your doctor what vaccines you might need before you start and while you are taking mercaptopurine. You should not have a live vaccine while taking mercaptopurine.

How should you take it?

Take mercaptopurine regularly as directed with a glass of water. Swallow the tablets whole – do not break, crush or chew.

What if you forget a dose?

If it is nearly time for your next dose, skip the missed dose and take your next dose at the usual time. Otherwise, take the missed dose as soon as you remember. Do not take two doses at the same time.

Can you take other medicines?

Tell your pharmacist or doctor about all medicines or treatments that you may be taking, including vitamins, herbal products (e.g. echinacea) or recreational drugs.

What side effects might you notice?

Side EffectsRecommended action

Reduced number of blood cells that fight infections or help your blood to clot - symptoms include: fever, chills, sore throat or generally feeling unwell, or easy or unusual bruising or bleeding

Severe stomach pain

Symptoms of liver problems including: yellow skin or eyes, itching, dark urine, pale bowel motions, abdominal pain

Tell your doctor immediately

Skin rash

Tell your doctor

Vomiting, diarrhoea

Tell your doctor if troublesome

Nausea

Take with food

If you notice any other effects, discuss them with your doctor or pharmacist.

Other information:

  • You will need regular blood tests while you are taking mercaptopurine to check if it is causing problems with your liver or blood, and to make sure you are on the right dose.
  • Protect yourself from too much sunlight while taking immunosuppressant medicines (they may increase your risk of skin cancer). Always cover up and apply a thick layer of broad spectrum sunscreen (at least SPF30) when outside. Do not use sunbeds.
  • Women using mercaptopurine for a long time may need cervical screening more often. Discuss with your doctor.
  • It is important to tell anyone who gives you medical or dental treatment that you are taking mercaptopurine.

This leaflet contains important, but not all, information about this medicine.

Prepared by the MyMedicines Committee at Christchurch Hospital, Te Whatu Ora - Waitaha, New Zealand. March 2023

For more general information about this sheet and its contents, see: What does a My Medicines sheet cover?

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About My Medicines

My Medicines Patient Information Leaflets (PILs) contain important, but not all, information about the medicines they describe.

For more information about the sheets, see: What does a My Medicines sheet cover?

My Medicines is developed by a team at Te Whatu Ora – Waitaha. Our team is made up of doctors, pharmacists, and a non-medical person to help us keep to plain language. We also discuss our information with specialist health professionals or groups when needed