Like all medicines, azathioprine can cause side effects, but not everyone gets them.
Common side effects
This common side effect of azathioprine happens in more than 1 in 10 people when first starting treatment or when the dose is increased. You'll usually feel better after a week or so. There are things you can do to help cope:
Feeling sick (mild nausea)
Stick to simple meals and do not eat rich or spicy food. It might help to take azathioprine after you have had a meal or snack.
Talk to your doctor if the advice on how to cope does not help and side effects do not go away or they get worse.
Serious side effects
Some people can have serious side effects when taking azathioprine.
Stop taking the medicine and speak to a doctor or call 111 now if:
- you feel tired all the time, dizzy or sick, or you're vomiting or have diarrhoea
- you have a high temperature with shivering or chills, cough or a sore throat
- your joints or muscles are hurting
- your pee changes colour or you start peeing more or less than usual – this can be a sign of kidney problems
- you feel confused, light-headed or weak – these can be signs of low blood pressure
- you're bleeding or bruising more easily than usual
- you notice lumps anywhere on your body
- you have severe stomach ache (abdominal pain) and back pain
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to azathioprine.
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Long-term side effects
Taking azathioprine for a long time can increase your chance of getting certain types of cancer, including skin cancer. For this reason, avoid strong sunlight and use a sunscreen (SPF 30 or more), and wear clothes that cover your arms and legs.
Azathioprine can also sometimes affect your liver, kidneys or bone marrow. You'll have regular blood tests while taking it to check for any problems.
Other side effects
These are not all the side effects of azathioprine. For a full list, see the leaflet inside your medicine packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.