Welcome to Mayo Clinic Connect!
I’m including a list of more common side effects of Imuran.
I took Imuran for 7 months. My main concern was multiple infections I got while on it.
Let’s see if anyone else will respond with a post!

Azathioprine
OVERVIEW
What is azathioprine (Imuran®)?

Azathioprine (Imuran®) is a medication that treats diseases that have to do with your immune system. It’s been used in some patients with multiple sclerosis (MS), usually if they have problems with standard FDA-approved medications for their MS.

Studies have shown that azathioprine can reduce the number of flare-ups in patients with relapsing MS. It also can reduce new MRI lesion formation. Azathioprine might also be used with other medications to boost their effects. It is not FDA approved specifically for MS.

How is azathioprine (Imuran®) taken?

Azathioprine comes in tablet-form, and it’s swallowed (oral).

Your white blood cell count and your weight determine the dosage of azathioprine that is prescribed. The starting dose is low and is slowly increased. Azathioprine is generally taken twice a day. It is available in 50 mg tablets, which may be easily broken in half if necessary. You may take this medication with food to reduce nausea and abdominal symptoms.

Your prescription label tells you how much to take of each dose and how often to take it. Follow these instructions carefully, and ask your pharmacist or healthcare provider to explain anything you don’t understand.

It is important that you take this medicine regularly as prescribed. Do not stop taking it unless you are directed to do so. Do not take more or less of the medicine than is prescribed.

Special instructions

Some mild nausea often occurs when you start taking azathioprine. This discomfort is expected and will go away as your body gets used to the medicine. If you have extreme nausea with vomiting, contact your healthcare provider.
Do not take azathioprine during pregnancy and breastfeeding.
While you are taking this medicine, you might be asked to have regular blood tests (blood cell counts and liver function tests) to evaluate the medicine's effectiveness and to keep an eye on your response to the medicine. Keep all appointments with your healthcare provider and the laboratory.
Your healthcare provider might reduce or even stop azathioprine when you are being treated for certain infections. This allows your body to effectively fight the infections.
Be sure you always have enough medicine on hand. Check your supply before holidays or other occasions when you might be unable to fill your prescription.
Do not have any vaccinations without your healthcare provider's approval.
Take precautions to avoid infection while taking this medicine. Avoid anyone who might have an infection and report any signs of infection to your healthcare provider.
Check to make sure there are no interactions with other medicines you take. A pharmacist can assist with this. ACE inhibitors are specifically not recommended to take with azathioprine as they might reduce the white blood cell count.
What are the possible side effects of azathioprine (Imuran®)?

Most people handle this medicine very well. It is important to remember that not everyone experiences all of these side effects. Even though some of the side effects could be serious, remember that precautions will be taken to detect and treat them before they become harmful. You should call your healthcare provider if any of the following reactions occur:

Increased stomach irritation, abdominal pain.
Nausea and vomiting.
Changes in hair color and texture, along with hair loss. (These changes are usually temporary.)
Loss of appetite.
Blood in the urine or stool.
Unusual bruising.
Fatigue.
Development of mouth sores and ulcers.
Decreased resistance to infection. (Because azathioprine is an immunosuppressive medicine, it can lower the number of white blood cells in your blood, increasing the chance of getting an infection.)
Long-term use may increase the risk of developing some types of tumors. This generally occurs after 10 years of continuous use or with a lifetime dose of 600 grams.
What should I do if I forget to take a dose?

If you forget to take a dose, take it as soon as you remember and then continue to follow your regular schedule.

What storage conditions are necessary for this drug?

Store this medicine at room temperature.
Do not store this medicine in direct heat or light.
Do not store this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture might cause it to break down.
Keep this medicine in the container it came in, tightly sealed.
Do not keep outdated medicine.
Keep this and other medicines out of the reach of children.
When should I call my healthcare provider?

Call your healthcare provider right away if you have any of these warning signs of infection:

Fever over 100°F (38°C). Sweats or chills.
Skin rash. Pain, tenderness, redness, or swelling.
Wound or cut that won't heal. Red, warm, or draining sore.
Sore throat, scratchy throat, or pain when swallowing.
Sinus drainage, nasal congestion, headaches, or tenderness along your upper cheekbones.
Persistent dry or moist cough that lasts more than two days. White patches in your mouth or on your tongue.
Nausea, vomiting, or diarrhea.
Flu-like symptoms (chills, aches, headache, or fatigue).
Trouble urinating: pain, burning, constant urge, or frequent urination. Bloody, cloudy, or foul-smelling urine, or black, tarry stools.
Call your healthcare provider if you have any other symptoms that cause concern.