Azathioprine is an immunosuppressant medication that calms an overactive immune system to treat autoimmune diseases and prevent organ transplant rejection.

If your doctor has prescribed Azathioprine — or you've seen it mentioned in connection with a condition you're managing — you probably have questions. What exactly does it do? Is it safe? How much will it cost? This guide covers everything you need to know in plain language.

What Is Azathioprine?

Azathioprine is a prescription medication in the purine antimetabolite class of immunosuppressants. It's been in use since the 1960s, making it one of the longest-standing immunosuppressive drugs available.

It's sold under two brand names:

• Imuran — originally made by Prometheus Laboratories, now marketed by Sebela Pharmaceuticals
• Azasan — made by Salix Pharmaceuticals (Bausch Health)

Generic Azathioprine is widely available from multiple manufacturers, and it's the form most patients receive. It is not a controlled substance — no special DEA scheduling or restrictions apply.

What Is Azathioprine Used For?

Azathioprine has two FDA-approved uses:

1. Prevention of organ transplant rejection — primarily kidney transplants, used alongside other immunosuppressants like Cyclosporine or Tacrolimus (Prograf)
2. Severe rheumatoid arthritis — in adults whose disease hasn't responded to conventional treatments

However, Azathioprine is also widely used off-label for many other autoimmune and inflammatory conditions:

• Inflammatory bowel disease — both Crohn's disease and ulcerative colitis, typically as a steroid-sparing agent
• Systemic lupus erythematosus (SLE)
• Myasthenia gravis
• Autoimmune hepatitis
• Multiple sclerosis
• Pemphigus and other autoimmune skin disorders
• Vasculitis
• Dermatomyositis and polymyositis
• Severe eczema/atopic dermatitis (refractory cases)
• Uveitis
• Neuromyelitis optica (Devic's disease)
• Interstitial lung disease

The off-label uses are well-established in clinical practice, even though they don't appear on the official FDA label. Many medical guidelines recommend Azathioprine for these conditions.

How Is Azathioprine Taken?

Azathioprine comes in several forms:

• Oral tablets: 50 mg (Imuran and generic — scored, so you can split them), 75 mg (Azasan), and 100 mg (Azasan)
• Injectable solution: 100 mg/vial (azathioprine sodium, used in hospital settings)

Most patients take the oral tablet form. Here's what to know about taking it:

• Take with food or after meals to reduce nausea — the most common side effect
• Can be taken once daily or split into two doses
• Swallow whole with a full glass of water (do not crush non-scored tablets)
• Take at the same time each day for consistent blood levels

Typical Dosing

Dosing depends on the condition being treated and your body weight:

• Rheumatoid arthritis: Start at 1 mg/kg/day (usually 50-100 mg), may increase by 0.5 mg/kg/day every 6-8 weeks, up to a maximum of 2.5 mg/kg/day
• Transplant rejection prevention: Start at 3-5 mg/kg/day, maintenance dose typically 1-3 mg/kg/day
• IBD and other off-label uses: Generally 1-2.5 mg/kg/day

Your doctor will adjust your dose based on your response, lab results, and any side effects you experience.

Required Monitoring

Before starting Azathioprine, your doctor should order:

• TPMT and NUDT15 genetic testing — these enzymes affect how your body metabolizes Azathioprine. Certain genetic variants mean you need a lower dose or shouldn't take the drug at all.
• Baseline blood work — complete blood count (CBC) and liver function tests

Once you start, expect blood work every 1-2 weeks initially, then monthly once your dose is stable. This monitoring is non-negotiable — it catches potentially serious problems like bone marrow suppression before they become dangerous.

Who Should Not Take Azathioprine?

Azathioprine is not appropriate for everyone. You should not take it if you:

• Are allergic to Azathioprine or 6-Mercaptopurine (its active metabolite)
• Have TPMT or NUDT15 homozygous deficiency — this genetic condition causes dangerously high drug levels and severe bone marrow suppression
• Are pregnant and taking it for rheumatoid arthritis (Pregnancy Category D — may be used in transplant or lupus patients when benefits clearly outweigh risks)
• Have been previously treated with alkylating agents (Cyclophosphamide, Chlorambucil, Melphalan) for rheumatoid arthritis

Elderly patients and those with kidney impairment may need dose adjustments. Always provide your doctor with a complete list of medications and supplements you take, since Azathioprine has several important drug interactions.

How Much Does Azathioprine Cost?

The cost varies significantly depending on whether you have insurance, use coupons, and which pharmacy you visit:

• Generic Azathioprine 50 mg (30 tablets): $40-$70 without a coupon; as low as $13-$17 with a GoodRx coupon
• Generic Azathioprine 100 mg (100 tablets): Up to $464 at retail
• Brand-name Imuran and Azasan: Significantly more expensive than generic

Most insurance plans cover generic Azathioprine as a Tier 1 or Tier 2 medication, which means relatively low copays. Prior authorization may be required for certain off-label uses.

For a complete breakdown of savings options, including coupon cards, patient assistance programs, and online pharmacies, read our guide to saving money on Azathioprine.

Final Thoughts

Azathioprine is a time-tested immunosuppressant that remains a cornerstone of treatment for transplant patients and people with serious autoimmune conditions. It requires more monitoring than some medications, but that monitoring is what makes it safe to use long-term.

If your doctor has recommended Azathioprine, the next steps are genetic testing, baseline labs, and starting at a low dose with gradual adjustments. To understand how it actually works in your body, check out our guide on Azathioprine's mechanism of action explained in plain English.

Need to fill your prescription? Medfinder can help you find Azathioprine in stock at pharmacies near you.