Azathioprine side effects: what 2,501 FDA adverse event reports show
Who reports
2,501 reports · 99% serious · 753 with death outcome · 65% female
Used for
Azathioprine tablets are indicated as an adjunct for the prevention of rejection in renal homotransplantation. It is also indicated for the management of active rheumatoid arthritis to reduce signs and symptoms. Renal Homotransplantation: Azathioprine tablets are indicated as an adjunct for the prevention of rejection in renal homotransplantation.
What it is
DESCRIPTION Azathioprine, an immunosuppressive antimetabolite, is available in tablet form for oral administration. Each scored tablet contains 50 mg azathioprine, USP and the inactive ingredients corn starch, lactose monohydrate, magnesium stearate, povidone and stearic acid.
Boxed warning
- MALIGNANCY Chronic immunosuppression with azathioprine, a purine antimetabolite increases risk of malignancy in humans. Reports of malignancy include post-transplant lymphoma and hepatosplenic T-cell lymphoma (HSTCL) in patients with inflammatory bowel disease.
Causality screen of the 40 strongest signals
What the badges mean
- Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
- Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
- Lab value / disease marker A laboratory result, investigation or disease-activity marker (antibody positive, CRP abnormal, swollen joint count) not described in the label. These usually mirror the monitored disease or testing protocol rather than a drug effect; not screened further.
- Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.
Strongest disproportionality signals
Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 249 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Hand deformity | 385 | 254.3 231.6–279.3ROR 300.4 · χ² 94,066 / p <1e-300 | 243.8 EB05 224.0 · IC025 +7.4 3/3 methods agree | Not in label — unassessed | serious PRR 156.2 · ♀ 98% (drug 65%) · 91% clinician | no trial data cached |
| Helicobacter infection | 286 | 242.1 216.7–270.5ROR 273.3 · χ² 66,522 / p <1e-300 | 231.6 EB05 210.0 · IC025 +7.2 3/3 methods agree | Not in label — unassessed | serious PRR 144.7 · ♀ 100% (drug 65%) · 91% clinician | no trial data cached |
| Folliculitis | 285 | 238.0 213.0–266.0ROR 268.5 · χ² 65,186 / p <1e-300 | 227.9 EB05 206.5 · IC025 +7.2 3/3 methods agree | Not in label — unassessed | serious PRR 158.3 · ♀ 100% (drug 65%) | no trial data cached |
| Pemphigus | 326 | 225.9 203.8–250.3ROR 259.6 · χ² 70,873 / p <1e-300 | 217.1 EB05 198.0 · IC025 +7.2 3/3 methods agree | Not in label — unassessed | serious PRR 128.4 · ♀ 100% (drug 65%) · 92% clinician | no trial data cached |
| Coeliac disease | 253 | 221.9 197.1–249.9ROR 246.8 · χ² 53,999 / p <1e-300 | 212.7 EB05 191.6 · IC025 +7.0 3/3 methods agree | Not in label — unassessed | serious PRR 156.6 · ♀ 100% (drug 65%) · 91% clinician | no trial data cached |
| Bursitis | 257 | 182.6 162.4–205.3ROR 203.4 · χ² 45,251 / p <1e-300 | 176.3 EB05 158.9 · IC025 +6.8 3/3 methods agree | Not in label — unassessed | serious PRR 122.4 · ♀ 100% (drug 65%) · 90% clinician | no trial data cached |
| Hypercholesterolaemia | 196 | 175.4 153.1–201.0ROR 190.3 · χ² 33,130 / p <1e-300 | 169.0 EB05 150.0 · IC025 +6.7 3/3 methods agree | Not in label — unassessed | serious PRR 106.3 · ♀ 99% (drug 65%) | no trial data cached |
| Back injury | 217 | 171.5 150.8–195.1ROR 187.8 · χ² 35,897 / p <1e-300 | 165.7 EB05 148.0 · IC025 +6.7 3/3 methods agree | Not in label — unassessed | serious PRR 129.5 · ♀ 99% (drug 65%) | no trial data cached |
| Pericarditis | 328 | 168.4 152.1–186.5ROR 193.7 · χ² 53,373 / p <1e-300 | 163.5 EB05 149.2 · IC025 +6.9 3/3 methods agree | Not in label — unassessed | serious PRR 96.8 · ♀ 100% (drug 65%) · 91% clinician | no trial data cached |
| Synovitis | 353 | 167.3 151.7–184.5ROR 194.7 · χ² 57,094 / p <1e-300 | 162.6 EB05 148.9 · IC025 +6.9 3/3 methods agree | Not in label — unassessed | serious PRR 100.0 · ♀ 98% (drug 65%) · 91% clinician | no trial data cached |
| Wound infection | 178 | 139.6 121.1–161.1ROR 150.3 · χ² 23,972 / p <1e-300 | 135.4 EB05 119.5 · IC025 +6.4 3/3 methods agree | Not in label — unassessed | serious PRR 85.7 · ♀ 99% (drug 65%) | no trial data cached |
| Glossodynia (burning tongue/mouth pain) | 365 | 139.2 126.5–153.2ROR 162.8 · χ² 49,173 / p <1e-300 | 136.0 EB05 124.7 · IC025 +6.7 3/3 methods agree | Not in label — unassessed | serious PRR 115.4 · ♀ 100% (drug 65%) · 92% clinician | no trial data cached |
| Adverse reaction | 206 | 132.3 115.9–150.9ROR 144.1 · χ² 26,305 / p <1e-300 | 128.7 EB05 114.6 · IC025 +6.4 3/3 methods agree | Reporting / coding artifact | serious n=206 · ♀ 100% (drug 65%) · 91% clinician | no trial data cached |
| Joint range of motion decreased | 180 | 114.5 99.4–131.9ROR 123.3 · χ² 19,874 / p <1e-300 | 111.6 EB05 98.6 · IC025 +6.2 3/3 methods agree | Not in label — unassessed | serious PRR 83.8 · ♀ 100% (drug 65%) | no trial data cached |
| Wound | 320 | 97.7 88.1–108.3ROR 111.8 · χ² 30,201 / p <1e-300 | 96.0 EB05 87.5 · IC025 +6.2 3/3 methods agree | Not in label — unassessed | serious PRR 66.9 · ♀ 100% (drug 65%) · 91% clinician | no trial data cached |
| Contraindicated product administered | 347 | 97.6 88.5–107.7ROR 113.2 · χ² 32,745 / p <1e-300 | 96.0 EB05 87.8 · IC025 +6.2 3/3 methods agree | Reporting / coding artifact | serious PRR 70.0 · ♀ 95% (drug 65%) · 93% clinician | no trial data cached |
| Liver function test increased | 239 | 95.1 84.2–107.3ROR 105.0 · χ² 21,919 / p <1e-300 | 93.3 EB05 83.8 · IC025 +6.1 3/3 methods agree | Not in label — unassessed | serious PRR 85.4 · ♀ 99% (drug 65%) | no trial data cached |
| Obesity | 156 | 82.8 71.1–96.5ROR 88.3 · χ² 12,412 / p <1e-300 | 81.2 EB05 71.1 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious PRR 55.4 · ♀ 100% (drug 65%) | no trial data cached |
| Systemic lupus erythematosus | 339 | 81.1 73.5–89.6ROR 93.7 · χ² 26,541 / p <1e-300 | 80.0 EB05 73.1 · IC025 +6.0 3/3 methods agree | Not in label — unassessed | serious PRR 48.0 · ♀ 100% (drug 65%) · 91% clinician | no trial data cached |
| Hepatitis (liver inflammation) | 238 | 78.7 69.7–88.9ROR 86.9 · χ² 18,035 / p <1e-300 | 77.5 EB05 69.6 · IC025 +5.9 3/3 methods agree | Not in label — unassessed | serious PRR 46.2 · ♀ 96% (drug 65%) | no trial data cached |
| Fibromyalgia | 224 | 78.1 68.9–88.5ROR 85.7 · χ² 16,827 / p <1e-300 | 76.9 EB05 68.8 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious PRR 59.2 · ♀ 100% (drug 65%) | no trial data cached |
| C-reactive protein increased | 319 | 74.2 67.0–82.3ROR 84.9 · χ² 22,804 / p <1e-300 | 73.3 EB05 66.8 · IC025 +5.9 3/3 methods agree | Lab value / disease marker | serious PRR 44.6 · ♀ 97% (drug 65%) · 96% clinician | no trial data cached |
| Drug-induced liver injury | 265 | 72.7 64.8–81.5ROR 81.2 · χ² 18,528 / p <1e-300 | 71.7 EB05 64.7 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious PRR 42.3 · ♀ 100% (drug 65%) · 92% clinician | no trial data cached |
| Type 2 diabetes mellitus | 286 | 71.6 64.2–79.9ROR 80.8 · χ² 19,709 / p <1e-300 | 70.7 EB05 64.1 · IC025 +5.8 3/3 methods agree | Not in label — unassessed | serious PRR 43.6 · ♀ 100% (drug 65%) | no trial data cached |
| Irritable bowel syndrome | 180 | 71.3 61.9–82.1ROR 76.7 · χ² 12,305 / p <1e-300 | 70.1 EB05 62.0 · IC025 +5.6 3/3 methods agree | Not in label — unassessed | serious PRR 52.2 · ♀ 100% (drug 65%) | no trial data cached |
| Vasculitis | 89 | 64.5 52.6–79.2ROR 66.9 · χ² 5,462 / p <1e-300 | 63.2 EB05 52.9 · IC025 +5.2 3/3 methods agree | Not in label — unassessed | serious PRR 40.1 · ♀ 12% (drug 65%) | no trial data cached |
| Liver injury | 176 | 61.5 53.3–70.9ROR 66.1 · χ² 10,347 / p <1e-300 | 60.7 EB05 53.5 · IC025 +5.5 3/3 methods agree | Not in label — unassessed | serious PRR 36.8 · ♀ 100% (drug 65%) | no trial data cached |
| Taste disorder | 143 | 60.3 51.4–70.7ROR 63.9 · χ² 8,225 / p <1e-300 | 59.4 EB05 51.7 · IC025 +5.4 3/3 methods agree | Not in label — unassessed | serious PRR 70.0 · ♀ 100% (drug 65%) | no trial data cached |
| Gait inability | 236 | 60.2 53.3–68.0ROR 66.4 · χ² 13,608 / p <1e-300 | 59.5 EB05 53.4 · IC025 +5.5 3/3 methods agree | Not in label — unassessed | serious PRR 43.3 · ♀ 99% (drug 65%) | no trial data cached |
| Therapeutic product effect decreased | 316 | 60.1 54.2–66.7ROR 68.7 · χ² 18,226 / p <1e-300 | 59.5 EB05 54.2 · IC025 +5.6 3/3 methods agree | Reporting / coding artifact | serious PRR 68.6 · 91% clinician | no trial data cached |
| Full blood count abnormal | 75 | 60.1 48.0–75.1ROR 61.9 · χ² 4,270 / p <1e-300 | 58.8 EB05 48.5 · IC025 +5.0 3/3 methods agree | Lab value / disease marker | serious PRR 46.1 · ♀ 5% (drug 65%) | no trial data cached |
| Arthropathy | 378 | 57.2 52.1–62.8ROR 67.2 · χ² 20,736 / p <1e-300 | 56.7 EB05 52.0 · IC025 +5.6 3/3 methods agree | Not in label — unassessed | serious PRR 40.2 · ♀ 99% (drug 65%) · 92% clinician | no trial data cached |
| Blood cholesterol increased | 313 | 56.7 51.1–62.9ROR 64.6 · χ² 16,982 / p <1e-300 | 56.1 EB05 51.1 · IC025 +5.5 3/3 methods agree | Lab value / disease marker | serious PRR 49.7 · ♀ 100% (drug 65%) | no trial data cached |
| Psoriatic arthropathy | 269 | 56.5 50.4–63.3ROR 63.2 · χ² 14,532 / p <1e-300 | 55.9 EB05 50.5 · IC025 +5.5 3/3 methods agree | Not in label — unassessed | serious PRR 41.1 · ♀ 100% (drug 65%) | no trial data cached |
| Hepatic enzyme increased | 447 | 55.5 51.0–60.4ROR 67.4 · χ² 23,800 / p <1e-300 | 55.0 EB05 50.9 · IC025 +5.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 46.5 · ♀ 95% (drug 65%) | no trial data cached |
| Obstructive airways disorder | 69 | 52.2 41.3–65.9ROR 53.6 · χ² 3,392 / p <1e-300 | 51.2 EB05 41.8 · IC025 +4.8 3/3 methods agree | Not in label — unassessed | serious PRR 31.4 · ♀ 0% (drug 65%) | no trial data cached |
| Inflammation | 312 | 51.3 46.2–56.9ROR 58.5 · χ² 15,276 / p <1e-300 | 50.8 EB05 46.3 · IC025 +5.4 3/3 methods agree | Not in label — unassessed | serious PRR 39.6 · ♀ 93% (drug 65%) | no trial data cached |
| Impaired healing | 189 | 48.5 42.3–55.7ROR 52.4 · χ² 8,717 / p <1e-300 | 48.1 EB05 42.6 · IC025 +5.2 3/3 methods agree | Reporting / coding artifact | serious PRR 34.0 · ♀ 100% (drug 65%) | no trial data cached |
| Infusion related reaction (reaction during infusion) | 365 | 46.6 42.4–51.3ROR 54.4 · χ² 16,202 / p <1e-300 | 46.2 EB05 42.4 · IC025 +5.3 3/3 methods agree | Not in label — unassessed | serious PRR 34.0 · ♀ 95% (drug 65%) · 91% clinician | no trial data cached |
| Osteoarthritis | 231 | 45.9 40.5–51.9ROR 50.4 · χ² 10,057 / p <1e-300 | 45.5 EB05 40.7 · IC025 +5.2 3/3 methods agree | Not in label — unassessed | serious PRR 29.8 · ♀ 100% (drug 65%) | no trial data cached |
Trial evidence (ClinicalTrials.gov)
Most frequently reported reactions
By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Off label use (used outside approved label) | 931 | 9.0 8.6–9.5ROR 13.8 · χ² 6,897 / p <1e-300 | 9.0 EB05 8.5 · IC025 +3.1 3/3 methods agree | Reporting / coding artifact | serious PRR 9.8 · 94% clinician | no trial data cached |
| Drug ineffective (drug did not work) | 759 | 4.8 4.6–5.1ROR 6.5 · χ² 2,460 / p <1e-300 | 4.8 EB05 4.5 · IC025 +2.2 3/3 methods agree | Reporting / coding artifact | serious PRR 7.9 | no trial data cached |
| Condition aggravated | 695 | 19.3 18.2–20.6ROR 26.4 · χ² 12,222 / p <1e-300 | 19.3 EB05 18.1 · IC025 +4.1 3/3 methods agree | Reporting / coding artifact | serious PRR 17.1 | no trial data cached |
| Fatigue (tiredness) | 535 | 5.8 5.4–6.2ROR 7.1 · χ² 2,190 / p <1e-300 | 5.7 EB05 5.4 · IC025 +2.4 3/3 methods agree | Not in label — unassessed | serious PRR 6.4 · 91% clinician | no trial data cached |
| Arthralgia (joint pain) | 534 | 10.8 10.0–11.7ROR 13.5 · χ² 4,840 / p <1e-300 | 10.8 EB05 10.0 · IC025 +3.3 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 11.5 | no trial data cached |
| Drug intolerance | 462 | 40.5 37.2–43.9ROR 49.4 · χ² 17,732 / p <1e-300 | 40.2 EB05 37.2 · IC025 +5.1 3/3 methods agree | Reporting / coding artifact | serious PRR 38.2 · ♀ 95% (drug 65%) | no trial data cached |
| Headache | 454 | 6.1 5.6–6.6ROR 7.2 · χ² 1,982 / p <1e-300 | 6.0 EB05 5.6 · IC025 +2.4 3/3 methods agree | Not in label — unassessed | serious PRR 7.4 · ♀ 92% (drug 65%) | no trial data cached |
| Hepatic enzyme increased | 447 | 55.5 51.0–60.4ROR 67.4 · χ² 23,800 / p <1e-300 | 55.0 EB05 50.9 · IC025 +5.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 46.5 · ♀ 95% (drug 65%) | no trial data cached |
| Alopecia (hair loss) | 428 | 18.3 16.8–19.9ROR 21.9 · χ² 7,025 / p <1e-300 | 18.2 EB05 16.8 · IC025 +4.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 22.7 · ♀ 100% (drug 65%) · 91% clinician | no trial data cached |
| Pain | 421 | 5.7 5.3–6.3ROR 6.7 · χ² 1,693 / p <1e-300 | 5.7 EB05 5.3 · IC025 +2.4 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 5.3 · ♀ 92% (drug 65%) | no trial data cached |
| Intentional product use issue | 414 | 39.7 36.3–43.3ROR 47.3 · χ² 15,557 / p <1e-300 | 39.4 EB05 36.3 · IC025 +5.1 3/3 methods agree | Reporting / coding artifact | serious PRR 33.8 · 92% clinician | no trial data cached |
| Nausea | 411 | 4.4 4.0–4.8ROR 5.0 · χ² 1,106 / p 7e-243 | 4.3 EB05 4.0 · IC025 +2.0 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 4.9 · ♀ 89% (drug 65%) | no trial data cached |
| Malaise (feeling unwell) | 408 | 7.8 7.1–8.5ROR 9.1 · χ² 2,458 / p <1e-300 | 7.7 EB05 7.1 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 7.6 | no trial data cached |
| Rheumatoid arthritis | 404 | 30.1 27.5–32.9ROR 35.7 · χ² 11,346 / p <1e-300 | 29.9 EB05 27.6 · IC025 +4.7 3/3 methods agree | Labeled — boxed warning exact term | serious PRR 21.3 · ♀ 95% (drug 65%) | no trial data cached |
| Rash | 401 | 7.8 7.1–8.5ROR 9.1 · χ² 2,404 / p <1e-300 | 7.7 EB05 7.1 · IC025 +2.8 3/3 methods agree | Labeled adverse reaction exact term | serious PRR 10.1 · ♀ 90% (drug 65%) | no trial data cached |
Unlabeled candidate signals
These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.
- Hand deformity — n=385, PRR 254.3
- Helicobacter infection — n=286, PRR 242.1
- Folliculitis — n=285, PRR 238.0
- Pemphigus — n=326, PRR 225.9
- Coeliac disease — n=253, PRR 221.9
- Bursitis — n=257, PRR 182.6
- Hypercholesterolaemia — n=196, PRR 175.4
- Back injury — n=217, PRR 171.5
- Pericarditis — n=328, PRR 168.4
- Synovitis — n=353, PRR 167.3
✓ A hand-written Bradford Hill causality assessment exists for this drug: Azathioprine ↔ Bone-marrow suppression (pancytopenia).
Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.
Common questions
What are the most reported side effects of Azathioprine?
In FDA FAERS, the most frequently co-reported reaction terms for Azathioprine are fatigue, arthralgia, headache, hepatic enzyme increased, alopecia, pain. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.
Does Azathioprine have an FDA boxed warning?
Yes. The current FDA label carries a boxed warning: - MALIGNANCY Chronic immunosuppression with azathioprine, a purine antimetabolite increases risk of malignancy in humans. Reports of malignancy include post-transplant lymphoma and hepatosplenic T-cell lymphoma (HSTCL) in patients with inflammatory bowel disease.
Do FAERS signals prove that Azathioprine causes these side effects?
No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.
Sources & methods
- FDA label via openFDA (set ID 2ffa2fce-895d-469e-8667-b078560aec5f, effective 20250204; matched on
openfda.generic_name.exact:"AZATHIOPRINE") - Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
- FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA
count=aggregation, fieldpatient.drug.openfda.generic_name.exact, 289 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction - Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
- Seriousness and sex counts from openFDA
count=serious,patient.patientsex,seriousnessdeath
Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.