If you will be taking this medicine for a long time, it is very important that your doctor check you at regular visits for any problems or unwanted effects that may be caused by this medicine. Blood tests may be needed to check for unwanted effects.

Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using this medicine, tell your doctor right away.

Do not use this medicine if you are also taking mercaptopurine (Purinethol®). Using these medicines together could cause serious unwanted effects.

If you are using azathioprine for arthritis, make sure your doctor knows if you received chlorambucil (Leukeran®), cyclophosphamide (Cytoxan®, Neosar®), or melphalan (Alkeran®) to treat your arthritis in the past. Using azathioprine after these medicines may increase your risk for unwanted effects. Talk to your doctor if you have questions about this.

This medicine may increase your risk of getting certain types of cancer, especially of the skin, lymph system (lymphoma), or blood (leukemia). Talk to your doctor if you have concerns about this risk.

Use sunscreen or sunblock lotions with a sun protection factor (SPF) of at least 15 on a regular basis when you are outdoors. Wear protective clothing and hats, and stay out of direct sunlight between the hours of 10 a.m. and 3 p.m. Avoid sunlamps and tanning beds.

While you are being treated with azathioprine, and after you stop treatment with it, do not have any immunizations (vaccines) without your doctor's approval. Azathioprine may lower your body's resistance and the vaccine may not work as well or you might get the infection the vaccine is meant to prevent. In addition, you should not be around other persons living in your household who receive live virus vaccines because there is a chance they could pass the virus on to you. Some examples of live vaccines include measles, mumps, influenza (nasal flu vaccine), poliovirus (oral form), rotavirus, and rubella. Do not get close to them and do not stay in the same room with them for very long. If you have questions about this, talk to your doctor.

Azathioprine can temporarily lower the number of white blood cells in your blood, increasing the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:

• If you can, avoid people with infections. Check with your doctor as soon as possible if you think you are getting an infection or if you get a fever or chills, cough or hoarseness, lower back or side pain, or painful or difficult urination.
• Check with your doctor as soon as possible if you notice any unusual bleeding or bruising; black, tarry stools; blood in the urine or stools; or pinpoint red spots on your skin.
• Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your doctor before having any dental work done.
• Do not touch your eyes or the inside of your nose unless you have just washed your hands and have not touched anything else.
• Be careful not to cut yourself when you are using sharp objects such as a safety razor or fingernail or toenail cutters.
• Avoid contact sports or other situations where bruising or injury could occur.

Check with your doctor right away if you have more than one of these symptoms while you are using this medicine: severe nausea or vomiting; diarrhea; fever; rash; a general feeling of discomfort or illness; muscle or joint pain; lightheadedness or dizziness; or unusual tiredness or weakness. These could be symptoms of a serious reaction to the medicine in your bowel (intestine).

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

More common

• Black, tarry stools
• bleeding gums
• blood in the urine or stools
• chest pain
• cough or hoarseness
• fever or chills
• lower back or side pain
• painful or difficult urination
• pinpoint red spots on the skin
• shortness of breath
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• swollen glands
• unusual bleeding or bruising
• unusual tiredness or weakness

Rare 

• Abdominal or stomach pain or tenderness
• clay-colored stools
• dark urine
• decreased appetite
• fast heartbeat
• fever (sudden)
• headaches
• itching
• loss of appetite
• muscle or joint pain
• nausea, vomiting, and diarrhea (severe)
• redness or blisters on the skin
• swelling of the feet or lower legs
• unusual feeling of discomfort or illness (sudden)
• yellow eyes or skin

Incidence not known

• Abdominal or stomach cramps
• diarrhea
• difficulty with breathing
• difficulty with moving
• fat in the stool
• general feeling of illness
• pale skin
• sores on the skin
• sudden loss of weight
• troubled breathing with movement
• weight loss

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
More common
Nausea or vomiting (mild)
swollen joints
Incidence not known
Hair loss or thinning of the hair

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects.