Azathioprine & Mercaptopurine

If you’ve been prescribed azathioprine or mercaptopurine, or are considering it as an option, you’re not alone. These medicines are a common treatment for Crohn's Disease and Ulcerative Colitis, with around 6 out of 10 people with the conditions taking them at some point.

Our information can support you to make an informed decision about this  treatment that’s right for you. It looks at:

- what you can expect from treatment
- how the medicines work
- possible side effects
- stopping or changing treatment

This information doesn't replace advice from your doctor. You can find more information about your medicines at

Other names for these medicines
Why am I being treated with azathioprine or mercaptopurine?
How effective are azathioprine and mercaptopurine?
How do azathioprine and mercaptopurine work?
How long do they take to work?
How do I take azathioprine and mercaptopurine?
How much should I take?
How long will I be taking azathioprine or mercaptopurine?
Are azathioprine and mercaptopurine used in combination with other medicines for Crohn's or Colitis?
What checks will I need before treatment has started?
Do I need ongoing checks?
Will I need to take any special precautions while being treated with azathioprine and mercaptopurine?
Can I have immunisation while on azathioprine and mercaptopurine?
Can I take other medicines
Can I drink alcohol while taking azathioprine and mercaptopurine?
Does azathioprine or mercaptopurine affect fertility or pregnancy?
What about breastfeeding?
What are the possible side effects?
Does taking azathioprine or mercaptopurine increase the risk of cancer?
Stopping or changing treatment
Who should I talk to if I'm worried?
Help and support from Crohn's & Colitis UK

Help us improve our information - let us know what you think by filling in our short survey.

How we write our information

Last reviewed: September 2019