methimazole Side Effects
Also known as: Tapazole
Analysis of 7,411 adverse event reports submitted to the FDA from 2004 to 2025.
Total Reports
7,411
Death-Related
615
8.3% of reports
Hospitalizations
2,710
36.6% of reports
Top Indication
Product Used For Unknown Indication
Most Reported Adverse Reactions
Who Reports Side Effects
Gender Distribution
Age Distribution
Reporting Trend by Year
Reactions in Death Reports
Top reactions reported in 615 reports where death was an outcome. These are voluntarily reported and do not establish causation.
| Reaction | Reports |
|---|---|
| DEATH | 172 |
| CARDIAC ARREST | 50 |
| MULTIPLE ORGAN DYSFUNCTION SYNDROME | 38 |
| PNEUMONIA | 37 |
| DRUG INEFFECTIVE | 33 |
| OFF LABEL USE | 33 |
| RESPIRATORY FAILURE | 31 |
| AGRANULOCYTOSIS | 26 |
| ACUTE KIDNEY INJURY | 24 |
| CARDIOGENIC SHOCK | 23 |
| SEPTIC SHOCK | 23 |
| NEUTROPENIA | 22 |
| FATIGUE | 21 |
| COMPLETED SUICIDE | 19 |
| DYSPNOEA | 19 |
| SEPSIS | 19 |
| ATRIAL FIBRILLATION | 18 |
| DIARRHOEA | 18 |
| CARDIO-RESPIRATORY ARREST | 17 |
| HYPERTHYROIDISM | 17 |
Reactions in Hospitalization Reports
Top reactions in 2,710 reports where hospitalization was an outcome.
| Reaction | Reports |
|---|---|
| DRUG INEFFECTIVE | 254 |
| HYPERTHYROIDISM | 206 |
| AGRANULOCYTOSIS | 185 |
| DYSPNOEA | 138 |
| FATIGUE | 133 |
| OFF LABEL USE | 128 |
| NAUSEA | 123 |
| PYREXIA | 115 |
| DIARRHOEA | 113 |
| ASTHENIA | 107 |
| FALL | 100 |
| PNEUMONIA | 99 |
| HEADACHE | 95 |
| THYROTOXIC CRISIS | 95 |
| DIZZINESS | 92 |
| PAIN | 90 |
| ANAEMIA | 89 |
| CARDIAC FAILURE | 88 |
| ATRIAL FIBRILLATION | 87 |
| WEIGHT DECREASED | 83 |
Nearby — Related Medications
What the FAERS Data Reveals About methimazole Side Effects
The FDA Adverse Event Reporting System (FAERS) contains 7,411 voluntary reports linked to methimazole and its brand equivalents (Tapazole), spanning 2004 through 2025. Of those, 615 (8.3%) listed death as an outcome and 2,710 (36.6%) involved hospitalization. The most common indication reported alongside adverse events was Product Used For Unknown Indication.
Demographic breakdowns help contextualize who is being exposed to the drug. Of reports with known sex, 72% were female and 28% male; age distribution skews toward 45-64, with 1,729 reports in that bracket. The single most reported reaction is drug ineffective with 607 submissions, followed by off label use and fatigue.
FAERS is a signal-detection tool, not a scorecard. Reports are voluntary, and a single case may list multiple suspect drugs, so numbers above should not be read as incidence rates or per-patient risk. Widely prescribed drugs naturally accumulate more reports than niche therapies even when individual risk is low. These aggregates are useful for spotting patterns that merit further pharmacovigilance, not for choosing between medications. This page is for educational reference only and is not medical advice — speak with a licensed clinician about any side-effect concerns.
Read our methodology — how this data is sourced, computed, and verified.