Mercaptopurine: adverse event reports filed with FDA

10,540

reports as suspect product

0.1% of all reports · about 469 a year

507

reports, 12 months to June 2026

677 in the 12 months before

95.8%

marked serious by the reporter

92.2% across the class

15%

record death among outcomes, as reported

1,584 reports · not verified by FDA

Reports by month, five years

Reports by the month FDA received them. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.

By year received

2026 covers reports received through June 2026 only.

Reactions recorded in the reports

share of Mercaptopurine reports recording the termmedian drug in nucleoside metabolic inhibitor

1. Febrile neutropeniafever with low white blood cells16.9%1,779
2. Pyrexiafever8.3%870
3. Off label useused for a purpose or in a way not on the label5.8%607
4. Drug ineffectivethe medicine did not work as expected5.5%576
5. Neutropenialow neutrophils, a type of white blood cell4.8%511
6. Vomitingbeing sick4.5%478
7. Nauseafeeling sick4.4%464
8. Sepsisa severe body-wide response to infection3.8%400
9. Pneumonialung infection3.7%390
10. Bacterial infectiona bacterial infection3.4%355
11. Pancytopenialow counts of all blood cells3.4%355
12. Abdominal painstomach or belly pain3.3%350
13. Anaemialow red blood cells3.3%344
14. Diarrhoealoose or frequent stools3.2%333
15. Myelosuppression3.1%328
16. Headachehead pain2.8%297
17. Viral infectiona viral infection2.7%288
18. Thrombocytopenialow platelets2.4%252
19. Platelet count decreasedlow platelet count2.4%248
20. Clostridium difficile colitisa bowel infection with C. difficile2.3%245
21. Secondary immunodeficiency2.3%239
22. Pancreatitisinflammation of the pancreas2.2%234
23. Alanine aminotransferase increasedraised liver enzyme (ALT)2.2%231
24. Deaththe patient died; cause not stated by this term2.1%222
25. Fatiguetiredness2.1%218
26. Hepatotoxicityliver injury2%210
27. Hypotensionlow blood pressure2%210
28. Coughcough1.9%200
29. Neutrophil count decreased1.9%195
30. Rhinovirus infection1.9%195

Top 30 of 1,585 MedDRA preferred terms recorded across these reports, with a plain-language gloss where one is available. One report can record several terms. The hollow bar is the median share across the 19 drugs in the nucleoside metabolic inhibitor class; it describes the reports, not the patients. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Outcomes recorded

Outcome flags as the reporter set them; a report can carry several, and "other serious" is FDA's own category for serious reports outside the named outcomes. Grey bar: all 313,386 reports in the class. FDA has not verified any outcome and states that the reports "cannot be used to estimate the incidence of these events."

Patients and reporters

Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 45.3% of reports give the United States as the country of the event or reporter.

Reason for use recorded

The indication field is filled in by the reporter and is often blank; shares are of all 10,540 reports.

Drugs most often listed in the same reports

Other products listed in reports where Mercaptopurine is a suspect product, whatever their own role. Co-listing means the two were recorded together; it says nothing about either product's part in the event. Only the 2,500 most-reported names are counted here.

In context

Shares are of reports, not of patients treated. The number of people taking a product is not in the data, so none of these figures is a rate, and differences between columns reflect who takes a product, who reports and how long it has been sold. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Other drugs in the nucleoside metabolic inhibitor class

Ordered by report count for navigation only. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic." A brand and its generic are separate rows because reporters name them separately.

Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. A report counts here when it lists Mercaptopurine as a suspect or interacting product; reports listing it only as a concomitant medication (6,879) are excluded. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.