Learn about common and serious Azasan (azathioprine) side effects, how to manage them, and when to call your doctor. Includes tips for specific populations.
Every medication comes with potential side effects, and Azasan (azathioprine) is no exception. As an immunosuppressant, Azasan works by dialing down your immune system to treat conditions like rheumatoid arthritis, prevent organ transplant rejection, and manage autoimmune diseases. That same immune-suppressing action is also what causes most of its side effects.
The good news? Most people tolerate Azasan well, especially once their body adjusts during the first few weeks. Knowing what to expect — and what warrants a phone call to your doctor — can help you feel more confident about your treatment and catch potential problems early.
Azasan is the brand name for azathioprine, a purine analog immunosuppressant. It belongs to the drug classes of antirheumatics and immunosuppressants. Azathioprine has been used since the 1960s and is FDA-approved for preventing kidney transplant rejection and treating rheumatoid arthritis. It's also widely used off-label for inflammatory bowel disease (Crohn's disease and ulcerative colitis), autoimmune hepatitis, lupus, myasthenia gravis, and several autoimmune skin conditions. For a deeper look, see our complete guide on What Is Azasan? Uses, Dosage, and What You Need to Know.
Side effects occur in roughly 15% to 28% of patients taking azathioprine. The most frequently reported side effects are typically mild and often improve as your body adjusts to the medication over the first few weeks of treatment.
Nausea is the single most common side effect of Azasan. It's dose-dependent, meaning higher doses tend to cause more stomach upset. Many patients find that nausea is worst during the first few weeks and gradually improves. Early-onset nausea often resolves without needing to change your dose.
Management tips:
Some patients experience loose stools, diarrhea, or general abdominal discomfort while taking Azasan. Like nausea, these symptoms are often dose-related and tend to improve over time. Staying hydrated and taking the medication with meals can help. If diarrhea is severe or persistent, contact your doctor — it could indicate a more serious issue like pancreatitis.
Hair thinning or hair loss (alopecia) is a known side effect of azathioprine. This can manifest as telogen effluvium (general thinning) or, more rarely, anagen effluvium (more significant hair loss). In most cases, hair loss is temporary and reversible once the medication is stopped or the dose is reduced. This side effect can be distressing, but it's important to discuss it with your doctor before stopping the medication on your own.
Rashes can occur during Azasan therapy. Mild skin rashes may resolve on their own or with dose adjustment. However, if you develop a widespread rash, hives, or signs of a more serious allergic reaction (swelling of the face, lips, or throat; difficulty breathing), seek medical attention immediately.
Feeling tired, weak, or generally unwell is common, especially early in treatment. Your body is adjusting to immune suppression, which can leave you feeling run down. This typically improves over time. If fatigue is severe or worsening, it could be a sign of bone marrow suppression — your doctor can check with a simple blood test.
Azasan can cause your red blood cells to become larger than normal (elevated MCV), which shows up on routine blood work. This is an expected pharmacological effect and doesn't necessarily indicate a problem on its own. Your doctor will monitor this as part of your regular blood work.
While less common, Azasan can cause serious side effects that require immediate medical attention. Your doctor will monitor for these with regular blood tests, but it's important to know the warning signs.
This is one of the most significant risks of Azasan therapy. Azathioprine can suppress your bone marrow's ability to produce blood cells, leading to:
The risk of bone marrow suppression is significantly higher in patients who take allopurinol simultaneously (used for gout), have kidney insufficiency, or have low TPMT/NUDT15 enzyme activity. This is why genetic testing is done before starting Azasan. Learn more about dangerous Azasan drug interactions.
Azasan can cause liver damage in two forms:
Watch for symptoms of liver problems: dark urine, yellowing of the skin or eyes (jaundice), severe nausea, loss of appetite, or pain in your upper right abdomen. Regular liver function tests are part of the standard monitoring protocol.
Because Azasan suppresses your immune system, you're more vulnerable to infections — including bacterial, viral, and fungal infections. Infections occur in approximately 7.4% of patients. Some of these infections can be serious or even fatal. The risk increases when Azasan is combined with corticosteroids (like prednisone).
Seek medical attention if you develop: fever, chills, persistent cough, sore throat, painful urination, or any unusual illness that doesn't improve.
Azasan carries an FDA boxed warning about an increased risk of certain cancers:
Protect yourself by wearing sunscreen (SPF 30+), protective clothing, and avoiding tanning beds. Have regular skin checks performed by your dermatologist.
Pancreatitis occurs in about 3.3% of patients, more commonly in women with Crohn's disease. It usually develops within the first six weeks of treatment. Symptoms include severe upper abdominal pain that may radiate to your back, nausea, and vomiting. If you experience these symptoms, contact your doctor immediately — Azasan should be discontinued if pancreatitis is confirmed.
In rare cases, Azasan may cause a serious brain infection called PML, which can lead to disability or death. Call your doctor right away if you notice problems with speech, thought, vision, or muscle movement. These symptoms may start gradually and worsen quickly.
Azasan can increase the risk of spontaneous miscarriage, low birth weight, and preterm delivery. If you're using Azasan for rheumatoid arthritis, you should not take it during pregnancy. However, the situation is more nuanced for conditions like lupus or after organ transplant, where the risks of stopping immunosuppression may outweigh the risks of the medication. Your doctor will help you weigh these decisions carefully.
Azathioprine's metabolite (6-MP) is present in breast milk, so breastfeeding is generally not recommended while taking Azasan. Discuss this with your doctor, as individual circumstances may vary.
Older adults may be more susceptible to side effects, particularly bone marrow suppression and infections. Doctors often use lower starting doses and more frequent blood monitoring in elderly patients. If you're over 65, make sure your doctor is aware of all your other medications to avoid interactions.
Patients with reduced TPMT (thiopurine S-methyltransferase) or NUDT15 (nucleotide diphosphatase) enzyme activity metabolize azathioprine differently, leading to higher levels of toxic metabolites in the body. This dramatically increases the risk of severe bone marrow suppression. Genetic testing before starting Azasan identifies these patients so that the dose can be adjusted — or an alternative medication selected.
Managing side effects is a key part of successful Azasan therapy. Here are practical strategies:
Azasan is a proven, effective immunosuppressant that has helped millions of patients manage organ transplant rejection, rheumatoid arthritis, and autoimmune conditions for over 60 years. While the list of potential side effects may seem daunting, most patients tolerate it well with proper monitoring. The key is regular blood work, open communication with your doctor, and knowing which symptoms to watch for.
If you're currently taking Azasan or about to start, stay informed:
Need to find a pharmacy that has Azasan in stock? Medfinder can help you locate it near you — without calling every pharmacy in town.
You focus on staying healthy. We'll handle the rest.
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