Methimazole adverse event reports that FDA received

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

Name type: Generic name
Class: Thyroid hormone synthesis inhibitor
Also reported as: Methimazole Tablets Usp, Methimazole Tablets

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 March 2004 to June 2026, FDA received 2,516 adverse event reports that name Methimazole. In these reports the drug is a suspect or interacting product.

In the same period, 5,389 further reports name it only as a concomitant medicine. The counts on this page do not include these reports.

FDA received 240 reports in the 12 months to June 2026 and 329 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, 240 (under 0.1%) name Methimazole. Reports from consumers or other non-health professionals were 15.2% of the reports that name Methimazole 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 Methimazole 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 54 reports that name Methimazole.
In January to March 2026, FDA received 48.
In April to June 2025, FDA received 69.

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 222 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 2,455 of the 2,516 reports (97.6%).

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 222 terms.

Reaction terms in the reports that name Methimazole, most reports first
Reaction term (MedDRA) and plain meaning	Reports	Share of the 2,516 reports
Drug ineffectivethe medicine did not work as expected	310	12.3%
Agranulocytosis	253	10.1%
Hyperthyroidismoveractive thyroid	182	7.2%
Off label useused for a purpose or in a way not on the label	131	5.2%
Foetal exposure during pregnancythe unborn baby was exposed to the medicine	93	3.7%
Thyrotoxic crisis	90	3.6%
Hypothyroidismunderactive thyroid	84	3.3%
Neutropenialow neutrophils, a type of white blood cell	76	3%
Drug-induced liver injury	74	2.9%
Pyrexiafever	68	2.7%
Rashskin rash	66	2.6%
Condition aggravatedthe condition being treated got worse	63	2.5%
Product use in unapproved indicationused for a purpose not on the label	60	2.4%
Pruritusitching	60	2.4%
Exposure during pregnancythe medicine was taken during pregnancy	58	2.3%
Product use issuea problem in how the product was used	57	2.3%
Maternal exposure during pregnancythe mother took the medicine during pregnancy	56	2.2%
Premature babya baby born early	56	2.2%
Treatment noncompliancethe treatment was not taken as directed	55	2.2%
Arthralgiajoint pain	50	2%
Pancytopenialow counts of all blood cells	43	1.7%
Febrile neutropeniafever with low white blood cells	41	1.6%
Nauseafeeling sick	41	1.6%
Drug hypersensitivityan allergic-type reaction (the term names a medicine)	40	1.6%
Drug interactionan interaction between medicines	40	1.6%
Headachehead pain	37	1.5%
Leukopenialow white blood cells	36	1.4%
Urticariahives	36	1.4%
Dyspnoeashortness of breath	35	1.4%
Diarrhoealoose or frequent stools	34	1.4%
Pleural effusionfluid around the lung	34	1.4%
Cardiac arrestthe heart stopped	33	1.3%
Septic shockshock arising from infection	33	1.3%
Oropharyngeal painsore throat	32	1.3%
Stevens-Johnson syndromea severe skin and mucous-membrane reaction	32	1.3%
Astheniaweakness or lack of energy	31	1.2%
Fatiguetiredness	31	1.2%
Dizzinesslight-headedness or unsteadiness	30	1.2%
Premature delivery	30	1.2%
Therapy non-responderthe treatment did not work	29	1.2%
Acute kidney injurysudden loss of kidney function	28	1.1%
Drug exposure during pregnancythe medicine was taken during pregnancy	28	1.1%
Jaundice cholestatic	28	1.1%
Liver injury	28	1.1%
Drug ineffective for unapproved indication	26	1%
Myalgiamuscle pain	26	1%
Polyarthritis	26	1%
Jaundiceyellowing of the skin or eyes	25	1%
Multiple organ dysfunction syndromeseveral organs failing	25	1%
Antithyroid arthritis syndrome	24	1%

Download all 222 terms of Methimazole (CSV)

The counts add to more than 2,516 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.

Outcomes by year

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

Outcomes in the reports that name Methimazole, 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	12	11	1	1	7	2	2	1	1
2005	13	12	1	0	4	1	2	5	1
2006	50	48	3	1	30	1	9	13	2
2007	8	7	0	0	7	0	0	0	1
2008	44	38	4	3	14	0	5	16	6
2009	23	17	0	3	12	0	0	7	6
2010	26	21	3	3	14	0	1	6	5
2011	62	50	4	5	25	1	8	24	12
2012	64	55	3	6	27	1	12	31	9
2013	38	29	0	5	14	2	0	15	9
2014	44	35	2	3	18	1	0	20	9
2015	90	76	13	6	41	4	0	41	14
2016	104	75	3	2	24	0	0	59	29
2017	160	129	16	14	60	2	4	91	31
2018	116	92	12	11	37	1	1	67	24
2019	127	96	7	10	43	1	8	66	31
2020	134	97	16	8	44	0	4	68	37
2021	139	113	9	13	48	1	4	86	26
2022	241	196	31	19	90	0	4	140	45
2023	227	208	14	22	99	0	1	146	19
2024	381	333	27	62	188	1	3	222	48
2025	296	272	13	46	175	0	7	185	24
2026	117	106	10	25	66	0	1	64	11

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 Methimazole, 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 Methimazole, by the year in which FDA received them
Year	Reports
2004	11
2005	13
2006	36
2007	20
2008	46
2009	24
2010	23
2011	58
2012	72
2013	40
2014	46
2015	107
2016	113
2017	147
2018	135
2019	132
2020	143
2021	136
2022	228
2023	227
2024	385
2025	272
2026	102

Reports that name Methimazole, 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 Methimazole
Age	Reports	Share
Under 2	19	0.8%
2 to 11	54	2.1%
12 to 17	126	5%
18 to 44	675	26.8%
45 to 64	555	22.1%
65 to 74	236	9.4%
75 and over	185	7.4%
Age not given	666	26.5%

Sex of the patient in the reports that name Methimazole
Sex	Reports	Share
Female	1,524	60.6%
Male	645	25.6%
Unknown or not given	347	13.8%

Type of reporter in the reports that name Methimazole
Reporter	Reports	Share
Physician	669	26.6%
Pharmacist	116	4.6%
Other health professional	1,260	50.1%
Lawyer	1	under 0.1%
Consumer or non-health professional	383	15.2%
Not given	87	3.5%

Age and sex are as the report gives them. The reporter is the primary source in the report. 61.1% of the reports give the United States as the country.

Reason for use

Reason for use (indication) that the reports of Methimazole record
Indication as recorded (MedDRA)	Reports	Share
Hyperthyroidism	834	33.1%
Graves' disease	327	13%
Basedow's disease	296	11.8%
Thyrotoxic crisis	102	4.1%
Basedow's disease	60	2.4%
Thyroid disorder	37	1.5%

The reporter fills in the indication, and the field is often empty. Each share is of all 2,516 reports.

Drugs in the same reports

Other drugs that the reports of Methimazole name, in any role, in order of name
Drug	Reports that name the two
Amiodarone	127
Aspirin	75
Atenolol	82
Cholestyramine	87
Hydrocortisone	147
Levothyroxine	69
Metoprolol	140
Prednisone	128
Propranolol	410
Propylthiouracil	211

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

Propylthiouracil same class
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Methamphetamine hcl next in the A to Z list
Methotrexate next in the A to Z list
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Methadose next in the A to Z list
Methotrexate sodium next in the A to Z list
Methadone hydrochloride 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 MethimazoleThe 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.

Cite this page

Reported Reactions. Methimazole: adverse event reports that FDA received. https://reportedreactions.com/drug/methimazole/ 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 Methimazole as a suspect or interacting product. The 5,389 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 Methimazole 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 Methimazole?

No. It is a count of what people reported to FDA: 2,516 reports from March 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 (50.1%), physician (26.6%) and consumer or non-health professional (15.2%). 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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