Your Side Effects May IncludeMethimazole (Tapazole) side effects
This side effect is printed on the FDA label for Methimazole. It was a question in our daily quiz, where you pick the real side effect from four choices.
A sudden, dangerous drop in infection-fighting white blood cells
It's called agranulocytosis and can appear within hours to days.
From the FDA label
“Agranulocytosis is potentially a life-threatening adverse reaction of methimazole therapy.”
Methimazole label, updated Sep 9, 2026 ·
Read the full label on DailyMed
What to watch for
Call your doctor right away for fever or a sore throat.
259 reports to the FDA's adverse event system mention agranulocytosis. A report is not proof the drug caused it. See the query
From quiz No. 20 · October 14, 2026 · Play that quiz →
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