Drugs › Thyroid hormone synthesis inhibitor
Generic name
Methimazole: adverse event reports filed with FDA
2,516 reports list it as a suspect or interacting product, 2004–2026. Class: Thyroid hormone synthesis inhibitor. Also reported as Methimazole Tablets Usp, Methimazole Tablets.
- 2,516
- reports as suspect product
- 0% of all reports · about 113 a year
- 240
- reports, 12 months to June 2026
- 329 in the 12 months before
- 84.1%
- marked serious by the reporter
- 87.2% across the class
- 7.6%
- record death among outcomes, as reported
- 192 reports · not verified by FDA
2,516 adverse event reports received by FDA list methimazole, a generic name as a suspect or interacting product, from March 2004 to June 2026. A further 5,389 reports list it only as a concomitant medication, and those are not counted in the figures on this page.
In the 12 months to June 2026, 240 reports listed it, down 27% from 329 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Over its reporting history that is about 113 reports a year and 0% of the 20,646,523 reports in the database, and 67.4% of the reports for the thyroid hormone synthesis inhibitor class. How many people take it is not in the data, so a count is not a rate of occurrence.
The MedDRA terms listed most often are drug ineffective (12.3%), agranulocytosis (10.1%) and hyperthyroidism (7.2%). A report can list several reactions, so shares add to more than 100%; 604 different terms appear across these reports. Drug ineffective is recorded in 12.3% of these reports, about the same share as in the median thyroid hormone synthesis inhibitor drug (11.7%).
84.1% of the reports are marked serious by the reporter (87.2% across the class); 7.6% record death among the outcomes and 43.2% record hospitalisation, as reported. 50.1% of the reports came from other health professionals, and the largest patient age group is 18 to 44 (26.8%). FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."
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 Methimazole reports recording the termmedian drug in thyroid hormone synthesis inhibitor
- Drug ineffectivethe medicine did not work as expected12.3%310
- Agranulocytosis10.1%253
- Hyperthyroidismoveractive thyroid7.2%182
- Off label useused for a purpose or in a way not on the label5.2%131
- Foetal exposure during pregnancythe unborn baby was exposed to the medicine3.7%93
- Thyrotoxic crisis3.6%90
- Hypothyroidismunderactive thyroid3.3%84
- Neutropenialow neutrophils, a type of white blood cell3%76
- Pyrexiafever2.7%68
- Rashskin rash2.6%66
- Condition aggravatedthe condition being treated got worse2.5%63
- Product use in unapproved indicationused for a purpose not on the label2.4%60
- Pruritusitching2.4%60
- Exposure during pregnancythe medicine was taken during pregnancy2.3%58
- Product use issuea problem in how the product was used2.3%57
- Maternal exposure during pregnancythe mother took the medicine during pregnancy2.2%56
- Premature babya baby born early2.2%56
- Treatment noncompliancethe treatment was not taken as directed2.2%55
- Arthralgiajoint pain2%50
- Pancytopenialow counts of all blood cells1.7%43
- Febrile neutropeniafever with low white blood cells1.6%41
- Nauseafeeling sick1.6%41
- Drug hypersensitivityan allergic-type reaction to a medicine1.6%40
- Drug interactionan interaction between medicines1.6%40
- Headachehead pain1.5%37
- Leukopenialow white blood cells1.4%36
- Urticariahives1.4%36
- Dyspnoeashortness of breath1.4%35
- Diarrhoealoose or frequent stools1.4%34
Top 30 of 604 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 2 drugs in the thyroid hormone synthesis 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 3,734 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
Patient age
Patient sex
Who reported
Age and sex as stated in the report; the reporter's qualification is the primary source recorded by FDA. 61.1% of reports give the United States as the country of the event or reporter.
Reason for use recorded
| 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 indication field is filled in by the reporter and is often blank; shares are of all 2,516 reports.
Drugs most often listed in the same reports
| Drug (any role in the report) | Reports | Share of Methimazole reports |
|---|---|---|
| Propranolol | 410 | 16.3% |
| Propylthiouracil | 211 | 8.4% |
| Hydrocortisone | 147 | 5.8% |
| Metoprolol | 140 | 5.6% |
| Prednisone | 128 | 5.1% |
| Amiodarone | 127 | 5% |
| Cholestyramine | 87 | 3.5% |
| Atenolol | 82 | 3.3% |
| Aspirin | 75 | 3% |
| Levothyroxine | 69 | 2.7% |
Other products listed in reports where Methimazole 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
| Measure | Methimazole | Thyroid hormone synthesis inhibitor | All reports |
|---|---|---|---|
| Reports as suspect product | 2,516 | 3,734 | 20,646,523 |
| Share of that pool | — | 67.4% | 0% |
| Reports, latest 12 months | 240 | — | 1,332,454 |
| Marked serious | 84.1% | 87.2% | 57.4% |
| Death recorded among outcomes, per 1,000 reports | 76 | 77 | 91 |
| Hospitalisation recorded, per 1,000 reports | 432 | 451 | 213 |
| Consumer-filed share | 15.2% | 12.1% | 45.8% |
| Top term, share of reports | Drug ineffective 12.3% | median 11.7% | 6.3% |
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 thyroid hormone synthesis inhibitor class
| Drug | Name type | Reports | Latest 12 months | Marked serious |
|---|---|---|---|---|
| Propylthiouracil | generic | 1,218 | 111 | 93.6% |
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.
Questions about Methimazole reports
How many adverse event reports has FDA received for Methimazole?
2,516 reports list Methimazole as a suspect or interacting product in the openFDA FAERS release of 28 Sep 2026, covering reports received through June 2026. 240 of them arrived in the latest 12 months. Another 5,389 list it only as a concomitant medication.
What reactions are recorded in Methimazole reports?
drug ineffective (12.3%), agranulocytosis (10.1%), hyperthyroidism (7.2%), off label use (5.2%) and foetal exposure during pregnancy (3.7%). These are MedDRA preferred terms coded from what the reporter described; a report can list several, and a term's presence is not a finding that Methimazole was responsible.
How serious are the reports?
84.1% are marked serious by the reporter. Among the outcomes recorded, 7.6% of reports include death and 43.2% include hospitalisation. FDA has not verified these outcomes and states that the reports "cannot be used to estimate the incidence" of the events.
Who files these reports?
other health professional (50.1%), physician (26.6%) and consumer or non-health professional (15.2%). Most reports reach FDA through the manufacturer, which must forward reports it receives.
Are reports for Methimazole rising?
240 reports in the 12 months to June 2026, down 27% from 329 in the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Counts also move with how many people take a product, its time on the market and publicity.
Do these reports show that Methimazole was responsible for these reactions?
No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event." The reaction may relate to the condition being treated, to other medicines, or to something else.
Is this a list of the side effects of Methimazole?
No. It is a count of what was reported to FDA. The adverse reactions observed in clinical studies are printed on the FDA-approved label, which a pharmacist or clinician can go through with you.
How do I report an adverse event?
Consumers and health professionals can report to FDA through MedWatch (Form FDA 3500 online, or 1-800-FDA-1088), or to the manufacturer, which must pass reports on. See the guide on how to report.
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 Methimazole as a suspect or interacting product; reports listing it only as a concomitant medication (5,389) 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.
Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.