Mercaptopurine adverse event reports that FDA received

Name: Reaction terms in FDA adverse event reports that name Mercaptopurine
Creator: Reported Reactions
License: https://creativecommons.org/publicdomain/zero/1.0/

Name type: Generic name
Class: Nucleoside metabolic inhibitor
Also reported as: Mercaptopurine Tablets Usp 50mg, 6 Mercaptopurine, Mercaptopurine Tab 50mg

What a report is

A report is not proof that the drug was the cause of the event.

FDA says:

Adverse event reports submitted to FDA do not undergo extensive validation or verification. Therefore, a causal relationship cannot be established between product and reactions listed in a report. While a suspected relationship may exist, it is not medically validated and should not be the sole source of information for clinical decision making or other assumptions about the safety or efficacy of a product. Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product.
Source: openFDA, Drug Adverse Event Overview, section "Responsible use of the data". The site read the page on 2 Oct 2026. The data have the reports that FDA received through 30 Jun 2026.

FDA also says:

There is no certainty that the reported event (adverse event or medication error) was actually due to the product. FDA does not require that a causal relationship between a product and event be proven, and reports do not always contain enough detail to properly evaluate an event. The information in these reports has not been scientifically or otherwise verified as to a cause and effect relationship and cannot be used to estimate the incidence of these events.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

Do not rely on openFDA to make decisions regarding medical care. While we make every effort to ensure that data is accurate, you should assume all results are unvalidated.
Source: openFDA, Response of the drug event API (meta.disclaimer). The site read the page on 2 Oct 2026.

Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.

Drug reports received through 30 Jun 2026. Device reports have a separate cutoff, 30 Sep 2026. Why a report count is not a rate.

Reports on file

From January 2004 to June 2026, FDA received 10,540 adverse event reports that name Mercaptopurine. In these reports the drug is a suspect or interacting product.

In the same period, 6,879 further reports name it only as a concomitant medicine. The counts on this page do not include these reports.

FDA received 507 reports in the 12 months to June 2026 and 677 in the 12 months before. FDA releases FAERS data every quarter, so the newest months are not complete. They grow in later releases.

Of the 1,332,454 drug reports that FDA received in the 12 months to June 2026, 507 (under 0.1%) name Mercaptopurine. Reports from consumers or other non-health professionals were 7% of the reports that name Mercaptopurine and 45.8% of all drug reports.

The number of people who use the product is not in the data. A count is not a rate. A count of reports is not a count of events or of patients, because one event can have more than one report.

There are many instances of duplicative reports and some reports do not contain all the necessary information.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of 11 Mar 2026. The site read the page on 2 Oct 2026.

Suspect product

FDA records each drug in a report as suspect, concomitant or interacting. This page counts the reports in which Mercaptopurine is suspect or interacting. FDA says:

Any number of the drugs may be marked as suspect if thought to be responsible for one or more of the reactions, but that information is not validated.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

Data version

openFDA FAERS release of 29 Oct 2026. Reports received through 30 Jun 2026.

Since the last update

FDA says:

Many factors can influence whether or not an event will be reported, such as the time a product has been marketed and publicity about an event.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

The information in these reports cannot be used to estimate the incidence (occurrence rates) of the events reported.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of 11 Mar 2026. The site read the page on 2 Oct 2026.

The latest update of the FDA data, recorded on 28 Oct 2026, changed no count of this page.

In April to June 2026, FDA received 137 reports that name Mercaptopurine.
In January to March 2026, FDA received 104.
In April to June 2025, FDA received 138.

April to June 2026 is the latest closed quarter in the data. A closed quarter is a quarter for which the FDA files have most of the reports.

All updates Feed of updates (RSS)

Reaction lookup

These are the reaction terms that the reports record, with the number of reports for each term. Type a term or a plain word to find its count.

What this list leaves out

The table lists the 858 reaction terms that 5 or more reports record. A term with fewer than 5 reports is not in the table.

The site keeps reaction terms for 10,501 of the 10,540 reports (99.6%).

The reports of the other years are not in the counts.

So a count in the table can be lower than the count of FDA.

Find a reaction term

The table shows the first 50 of 858 terms.

Reaction terms in the reports that name Mercaptopurine, most reports first
Reaction term (MedDRA) and plain meaning	Reports	Share of the 10,540 reports
Febrile neutropeniafever with low white blood cells	1,779	16.9%
Pyrexiafever	870	8.3%
Off label useused for a purpose or in a way not on the label	607	5.8%
Drug ineffectivethe medicine did not work as expected	576	5.5%
Neutropenialow neutrophils, a type of white blood cell	511	4.8%
Vomitingbeing sick	478	4.5%
Nauseafeeling sick	464	4.4%
Sepsisa severe body-wide response to infection	400	3.8%
Pneumonialung infection	390	3.7%
Bacterial infectiona bacterial infection	355	3.4%
Pancytopenialow counts of all blood cells	355	3.4%
Abdominal painstomach or belly pain	350	3.3%
Anaemialow red blood cells	344	3.3%
Diarrhoealoose or frequent stools	333	3.2%
Myelosuppression	328	3.1%
Headachehead pain	297	2.8%
Viral infectiona viral infection	288	2.7%
Thrombocytopenialow platelets	252	2.4%
Platelet count decreasedlow platelet count	248	2.4%
Clostridium difficile colitisa bowel infection with C. difficile	245	2.3%
Secondary immunodeficiency	239	2.3%
Pancreatitisinflammation of the pancreas	234	2.2%
Alanine aminotransferase increasedraised liver enzyme (ALT)	231	2.2%
Deaththe patient died; cause not stated by this term	222	2.1%
Fatiguetiredness	218	2.1%
Hepatotoxicityliver injury	210	2%
Hypotensionlow blood pressure	210	2%
Cough	200	1.9%
Neutrophil count decreased	195	1.9%
Rhinovirus infection	195	1.9%
Drug interactionan interaction between medicines	186	1.8%
Product use in unapproved indicationused for a purpose not on the label	186	1.8%
White blood cell count decreasedlow white cell count	186	1.8%
Condition aggravatedthe condition being treated got worse	178	1.7%
Crohn's disease	176	1.7%
Bronchopulmonary aspergillosis	175	1.7%
Venoocclusive liver disease	175	1.7%
Pseudomonal sepsis	169	1.6%
Cellulitisa skin infection	168	1.6%
Haematotoxicity	168	1.6%
Parainfluenzae virus infection	167	1.6%
Tachycardiafast heart rate	166	1.6%
Infectionan infection, type not specified	165	1.6%
Mycobacterium chelonae infection	164	1.6%
Human herpesvirus 6 infection	163	1.5%
Mucosal inflammation	162	1.5%
Leukopenialow white blood cells	161	1.5%
Osteonecrosis	159	1.5%
Respiratory failurethe lungs could not supply enough oxygen	159	1.5%
Septic shockshock arising from infection	154	1.5%

Download all 858 terms of Mercaptopurine (CSV)

The counts add to more than 10,540 reports, because one report can record more than one term. FDA says:

No individual drug is connected to any individual reaction. When a report lists multiple drugs and multiple reactions, there is no way to conclude from the data therein that a given drug is responsible for a given reaction.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

The CSV file has the same rows and the same limits. Its last row is a note that says so.

MedDRA term

The person who codes a report selects the preferred term that agrees best with the description of the reporter. The words under a term are the plain meaning that this site gives.

Not the label

The FDA-approved label of a product lists its adverse reactions. See the official pages at the end of this page.

Same ingredient, other names

Reporters write a brand name or a generic name. Each name has its own page and its own count.

Names of Mercaptopurine with a page, in the order generic names, brand names, names as reported
Name	Name type	Reports
Mercaptopurine (this page)	Generic name	10,540
Mercaptopurine monohydrate	Generic name	327

Sum of the separately reported names: 10,867. A report that names two of these names is in the sum two times. The sum is not the number of reports for the ingredient.

FDA says:

Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

Importantly, the AEMS data by themselves are not an indicator of the safety profile of the drug or biologic.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of 11 Mar 2026. The site read the page on 2 Oct 2026.

Outcomes by year

The table gives the outcomes that the reporters gave, in the terms of FDA.

Outcomes in the reports that name Mercaptopurine, by the year of the openFDA file that holds the report

The table continues to the right.

Year of the openFDA file	Reports	Serious	Death	Life-threatening	Hospitalization (initial or prolonged)	Disability or Permanent Damage	Congenital Anomaly/Birth Defect	Other Serious (Important Medical Events)	Not serious
2004	58	56	10	7	23	5	0	26	2
2005	75	57	20	1	29	1	0	24	18
2006	109	107	19	4	53	2	0	57	2
2007	119	115	42	1	45	2	0	47	4
2008	105	95	16	9	51	0	1	35	10
2009	207	195	32	12	135	3	0	76	12
2010	315	277	47	13	160	7	1	117	38
2011	217	191	22	8	103	0	2	91	26
2012	334	315	54	11	120	5	0	186	19
2013	212	199	37	14	95	4	0	102	13
2014	416	398	51	25	130	3	2	255	18
2015	356	335	100	16	144	1	0	166	21
2016	363	329	68	11	170	3	1	161	34
2017	601	570	83	26	266	3	0	368	31
2018	718	692	118	42	355	6	0	464	26
2019	833	777	194	40	376	7	8	465	56
2020	753	735	150	63	403	7	2	391	18
2021	965	941	80	107	564	8	0	548	24
2022	1,021	1,006	119	170	685	21	5	569	15
2023	951	928	106	123	516	4	2	632	23
2024	890	874	102	154	530	2	2	578	16
2025	646	633	72	91	354	9	0	499	13
2026	276	272	42	36	129	3	0	198	4

An outcome in a report is not proof that the drug was the cause. The reporter gives the outcome, and FDA does not verify it. FDA says:

The information in these reports has not been scientifically or otherwise verified as to a cause and effect relationship and cannot be used to estimate the incidence of these events.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

The six headings with the names of FDA are the outcome terms of FDA. A report can have more than one outcome. The columns Serious and Not serious are the two values of the openFDA field serious. For the value serious, openFDA gives this description:

The adverse event resulted in death, a life threatening condition, hospitalization, disability, congenital anomaly, or other serious condition
Source: openFDA, Drug adverse event fields (YAML reference). The site read the page on 2 Oct 2026.

The year is the year of the openFDA file that holds the latest version of the report. It is not always the year in which FDA first received the report. The chart of the next section uses the year of first receipt. The latest year is not complete.

Reports by year and month

Reports that name Mercaptopurine, by the year in which FDA received them

The column of 2026 has an outline, because the year is not complete. It has the reports that FDA received through June 2026 only.

Show the figures of the chart as a table

Reports that name Mercaptopurine, by the year in which FDA received them
Year	Reports
2004	53
2005	78
2006	110
2007	125
2008	103
2009	204
2010	329
2011	224
2012	353
2013	209
2014	423
2015	358
2016	374
2017	710
2018	901
2019	883
2020	797
2021	893
2022	1,020
2023	848
2024	775
2025	529
2026	241

Reports that name Mercaptopurine, by month, five years to June 2026

FDA releases FAERS data every quarter, so the newest months are not complete. They grow in later releases.

Why a count moves

A count moves for many reasons. The guide gives FDA's words about them.

Patients and reporters

Age of the patient in the reports that name Mercaptopurine
Age	Reports	Share
Under 2	297	2.8%
2 to 11	2,639	25%
12 to 17	1,391	13.2%
18 to 44	1,852	17.6%
45 to 64	897	8.5%
65 to 74	307	2.9%
75 and over	98	0.9%
Age not given	3,059	29%

Sex of the patient in the reports that name Mercaptopurine
Sex	Reports	Share
Female	3,733	35.4%
Male	4,861	46.1%
Unknown or not given	1,946	18.5%

Type of reporter in the reports that name Mercaptopurine
Reporter	Reports	Share
Physician	3,977	37.7%
Pharmacist	408	3.9%
Other health professional	4,248	40.3%
Lawyer	1	under 0.1%
Consumer or non-health professional	738	7%
Not given	1,168	11.1%

Age and sex are as the report gives them. The reporter is the primary source in the report. 45.3% of the reports give the United States as the country.

Reason for use

Reason for use (indication) that the reports of Mercaptopurine record
Indication as recorded (MedDRA)	Reports	Share
Acute lymphocytic leukaemia	3,583	34%
Crohn's disease	465	4.4%
Colitis ulcerative	438	4.2%
B precursor type acute leukaemia	434	4.1%
B-cell type acute leukaemia	276	2.6%
Crohn's disease	247	2.3%

The reporter fills in the indication, and the field is often empty. Each share is of all 10,540 reports.

Drugs in the same reports

Other drugs that the reports of Mercaptopurine name, in any role, in order of name
Drug	Reports that name the two
Asparaginase	1,394
Cyclophosphamide	4,035
Cytarabine	4,864
Daunorubicin	1,670
Dexamethasone	2,987
Methotrexate	6,728
Pegaspargase	1,577
Prednisone	2,779
Vincristine	3,377
Vincristine sulfate	2,826

The table has the 10 drug names that these reports name most. Two names in one report says only that the report recorded the two. It says nothing about the part of a product in the event.

FDA says:

Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

Importantly, the AEMS data by themselves are not an indicator of the safety profile of the drug or biologic.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of 11 Mar 2026. The site read the page on 2 Oct 2026.

Pages near this one

Mercaptopurine monohydrate same ingredient
Inqovi same class
Nelarabine same class
Inlexzo same class
Onureg same class
Gemcitabine hydrochloride same class
Pentostatin same class
Mepronizine next in the A to Z list
Mepron next in the A to Z list
Mercaptopurine/Mercaptopurine Anhydrous next in the A to Z list
Meprobamate next in the A to Z list
Mercilon next in the A to Z list

These links are for navigation. No count selected them. The class page lists each drug of the class.

Official pages

DailyMed labels for MercaptopurineThe labels (prescribing information) that have this name, at the National Library of Medicine.
MedWatch Online Voluntary Reporting FormThe online form of FDA for a voluntary report.
MedWatch: The FDA Safety Information and Adverse Event Reporting ProgramThe page of the FDA program that receives reports about drugs and devices.
FDA Adverse Event Monitoring System (AEMS) Public DashboardThe public dashboard of FDA for adverse event reports on drugs and biologics.

The site checked these addresses on 2 Oct 2026. The links open in a new tab.

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Reported Reactions. Mercaptopurine: adverse event reports that FDA received. https://reportedreactions.com/drug/mercaptopurine/ Source: U.S. Food and Drug Administration, openFDA Drug Adverse Event (FAERS) files, release of 29 Oct 2026. Reports received through 30 Jun 2026.

Where the data come from

The counts come from the openFDA Drug Adverse Event (FAERS) bulk files, release of 29 Oct 2026. The files have the reports that FDA received through 30 Jun 2026. A drug name is the name on the report. The site matches it to a brand name or a generic name of the National Drug Code Directory of 2 Nov 2026. A class is the pharmacologic class (EPC) of the FDA label.

A report is in the count when it names Mercaptopurine as a suspect or interacting product. The 6,879 reports that name it only as a concomitant medicine are not in the count. The site does not publish a report narrative, a lot number, a detail of a patient or the identity of a reporter. The record of FDA is the authority. See how the site counts reports, the data sources and the corrections page.

Questions

Do these reports show that Mercaptopurine was responsible for the reactions?

No. FDA says:

For any given report, there is no certainty that a suspected drug caused the event.
Source: FDA, FDA Adverse Event Monitoring System (AEMS) Public Dashboard. Content current as of 11 Mar 2026. The site read the page on 2 Oct 2026.

A reaction can relate to the condition that the drug treats, to other medicines, or to something else.

Is this the list of reactions on the label of Mercaptopurine?

No. It is a count of what people reported to FDA: 10,540 reports from January 2004 to June 2026. The FDA-approved label of a product lists its adverse reactions. The official pages at the end of this page link to the labels.

Who sent these reports?

Other health professional (40.3%), physician (37.7%) and consumer or non-health professional (7%). These are the types of reporter for the reports that name this drug.

If a manufacturer receives an adverse event report, it is normally required to send the report to FDA.
Source: openFDA, Drug Adverse Event Overview. The site read the page on 2 Oct 2026.

How does a person report an adverse event?

FDA runs MedWatch, a program that takes voluntary reports from health professionals, patients and consumers. The guide on how to report has the links.

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