Azathioprine (Imuran)

Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.

About Azathioprine

What it is

Azathioprine is an immunosuppressant of the thiopurine group: the body turns it into mercaptopurine, which slows the multiplication of immune cells. It is used after organ transplants, and for autoimmune and inflammatory conditions such as rheumatoid arthritis, inflammatory bowel disease and autoimmune hepatitis. It is sold as Imuran, among other names.

How genes come into it

Because azathioprine becomes mercaptopurine in the body, the same two genes matter. TPMT and NUDT15 make enzymes that inactivate the thiopurines; people with low-activity versions of either build up more of the active form, and the bone marrow is affected more strongly. Low-activity TPMT is most common in people of European and African ancestry, low-activity NUDT15 in people of East Asian and Hispanic ancestry. CPIC and DPWG have published guidelines on both genes, and the US drug label discusses them. Other genes such as ITPA have been studied, with weaker evidence.

Published guidelines

Clinical guidelines that name a gene for Azathioprine. They sort people into groups by the gene copies they carry.

CPIC guideline: NUDT15, TPMT. TPMT: Normal Metabolizer, Intermediate Metabolizer, Poor Metabolizer, Indeterminate, No Result, Possible Intermediate Metabolizer · NUDT15: Normal Metabolizer, Intermediate Metabolizer, Poor Metabolizer, Indeterminate, No Result, Possible Intermediate Metabolizer. Strong. 2026.

DPWG guideline: NUDT15. Normal Metabolizer · Intermediate Metabolizer · Poor Metabolizer · Indeterminate · Possible Intermediate Metabolizer. 2025.

DPWG guideline: TPMT. Normal Metabolizer · Intermediate Metabolizer · Poor Metabolizer · Indeterminate · Possible Intermediate Metabolizer. 2025.

US FDA: NUDT15, TPMT. TPMT: Normal Metabolizer, Intermediate Metabolizer, Poor Metabolizer, Indeterminate, No Result, Possible Intermediate Metabolizer · NUDT15: Normal Metabolizer, Intermediate Metabolizer, Poor Metabolizer, Indeterminate, No Result, Possible Intermediate Metabolizer.

What research found

Every published finding on gene variants and Azathioprine. Upload your DNA file to see which of these rows apply to you.

Rated evidence (21 rated variants)

PharmGKB weighs all studies of a variant and rates how strong the evidence is, from 1A (strongest) to 4.

TPMT TPMT*1, TPMT*2, TPMT*3A, TPMT*3B, TPMT*3C, TPMT*6: Level 1A · replicated. Toxicity: Leukopenia, Myelosuppression. 37.

NUDT15 rs116855232: Level 1A · replicated. Toxicity: Inflammatory Bowel Diseases, Myelosuppression. 17.

TPMT TPMT*1, TPMT*2, TPMT*3A, TPMT*3B, TPMT*3C: Level 1A · replicated. 9.

TPMT TPMT*1, TPMT*3A, TPMT*3C: Level 1A · replicated. Metabolism/PK. 3.

Metabolism (8 findings)

Studies of how quickly the body processes this medication.

GSTM1 GSTM1 non-null, GSTM1 null: GSTM1 null is associated with increased dose of azathioprine in people with Inflammatory Bowel Diseases as compared to GSTM1 non-null.

ITPA rs1127354: Genotype AC is associated with increased metabolism of azathioprine in people with Inflammatory Bowel Diseases as compared to genotype CC.

ITPA rs1127354: Genotypes AA + AC is associated with decreased metabolism of azathioprine or mercaptopurine in people with Inflammatory Bowel Diseases as compared to genotype CC.

TPMT TPMT low activity: TPMT low activity phenotype is associated with decreased metabolism of azathioprine and mercaptopurine as compared to TPMT high activity phenotype.

Response (10 findings)

Studies of how well it worked in people carrying a variant.

AOX1 rs55754655: Allele G is associated with decreased response to azathioprine in people with Inflammatory Bowel Diseases as compared to allele A.

GSTM1 GSTM1 non-null, GSTM1 null: GSTM1 null is associated with decreased clinical benefit to azathioprine in children with Colitis, Ulcerative or Crohn Disease as compared to GSTM1 non-null.

ITPA rs1127354: Genotypes AA + AC is associated with increased response to azathioprine in people with Lupus Erythematosus, Systemic as compared to genotype CC.

PACSIN2 rs2413739: Genotypes CT + TT is associated with decreased response to azathioprine in children with Irritable Bowel Syndrome as compared to genotype CC.

Dosing (17 findings)

Studies of how much of the drug people needed or tolerated.

AOX1 rs55754655: Genotypes AG + GG is associated with increased dose of azathioprine in people with Kidney Transplantation as compared to genotype AA.

MOCOS rs594445: Genotypes AA + AC is associated with decreased dose of azathioprine in people with Kidney Transplantation as compared to genotype CC.

NUDT15 rs116855232: Genotypes CT + TT are associated with decreased dose of azathioprine in people with Colitis, Ulcerative, Crohn Disease and Hepatitis, Autoimmune as compared to genotype CC.

NUDT15 rs116855232: Genotype CT is associated with decreased dose of azathioprine and mercaptopurine in people with Inflammatory Bowel Diseases as compared to genotype CC.

Side effects (3 findings)

Studies of side effects in people carrying a variant.

ITPA rs7270101: Genotypes AC + CC is associated with increased metabolism of azathioprine or mercaptopurine in people with Inflammatory Bowel Diseases or Precursor Cell Lymphoblastic Leukemia-Lymphoma as compared to genotype AA.

NUDT15 rs116855232: Genotype CT is associated with increased discontinuation of azathioprine or mercaptopurine in people with Inflammatory Bowel Diseases as compared to genotype CC.

NUDT15 rs116855232: Genotype TT is associated with decreased dose of azathioprine in people with Leukopenia as compared to genotype CC.

Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.

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Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.

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Content updated September 2026.

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