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What the label lists and what reports show

Methimazole side effects

Methimazole's FDA label lists its adverse reactions in its own words. FAERS holds 7,805 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is fatigue (445 reports).

  • Generic listed

Check it at the source: the methimazole FDA label on DailyMed (effective August 20, 2026, AiPing Pharmaceutical, Inc.); the FDA FAERS public dashboard.

What does the label list?

From the label: adverse reactions

Major adverse reactions (which occur with much less frequency than the minor adverse reactions) include inhibition of myelopoiesis (agranulocytosis, granulocytopenia, thrombocytopenia, and aplastic anemia), drug fever, a lupus-like syndrome, insulin autoimmune syndrome (which can result in hypoglycemic coma), hepatitis (jaundice may persist for several weeks after discontinuation of the drug), periarteritis, and hypoprothrombinemia. Nephritis occurs very rarely. There have been postmarketing case reports of acute pancreatitis. There are reports of a vasculitis, often associated with the presence of anti-neutrophilic cytoplasmic antibodies (ANCA), resulting in severe complications [see WARNINGS ]. …

Source: FDA drug label, AiPing Pharmaceutical, Inc., effective August 20, 2026 (SPL set 06bb4bcc-5e47-48b6-a76c-648f846704e8), via openFDA; the full label on DailyMed

What do FAERS reports show?

7,805 reports list methimazole among the medicines taken, each a report of something that happened, not proof the medicine caused it; 641 are coded as a death and 2,871 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 19 reactions below, 9 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

  • Drug Ineffective (a use or a product term, not a reaction)644
  • Off Label Use (a use or a product term, not a reaction)487
  • Fatigue445
  • Hyperthyroidism (a use or a product term, not a reaction)407
  • Nausea (named in the label)381
  • Diarrhoea335
  • Headache (named in the label)330
  • Pain310
  • Dizziness306
  • Dyspnoea (named in the label)277
  • Agranulocytosis (named in the label)259
  • Asthenia222
  • Arthralgia (named in the label)221
  • Anxiety213
  • Rash (named in the label)212
  • Condition Aggravated (a use or a product term, not a reaction)206
  • Pruritus (named in the label)205
  • Product Use In Unapproved Indication (a use or a product term, not a reaction)202
  • Weight Decreased193
  • Death (an outcome recorded in the report)182
  • Muscle Spasms178
  • Pyrexia178
  • Fall171
  • Malaise (named in the label)169
  • Vomiting (named in the label)168

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Methimazole: the full record
label, generics, price, shortages, recalls
Side effects hub
the most reported medicines and reactions