Methimazole
The first-line antithyroid medicine for Graves' disease.
VIDEO LESSON
How it's taken
• Once daily, adjusted to thyroid levels
• Often paired with a beta-blocker early on for symptoms
Side effects at a glance
• Rash or itching
• Joint aches
• Altered taste
Rare but serious
• Agranulocytosis (very low white cells)
• Liver injury
Monitoring
Free T4 and T3 every 4 to 6 weeks while adjusting, a baseline blood count and liver tests, and TSH receptor antibodies before stopping.
Good to know
Plan pregnancy with your clinician: current guidance favors switching to PTU before conception.
AT A GLANCE
Class
Thyroid
Brand names
Tapazole
Status
FDA-approved
Reviewed by
Farhan Tahir, MD
Is this medicine right for you?
Prescription medicines need individual medical advice. Dr. Tahir’s team offers consults through Youthful Medicine.
MECHANISM
How it works
Methimazole blocks thyroid peroxidase, the enzyme that builds thyroid hormone, so the gland makes less T4 and T3. Stored hormone is unaffected, so improvement takes weeks.
THE EVIDENCE
What the research actually shows.
EVIDENCE SUMMARY
Recommended first-line drug therapy for Graves' disease in ATA and ETA guidelines. A 12 to 18 month course leads to lasting remission in some people; longer low-dose treatment is an option.
KEY TRIALS
ATA 2016 and ETA 2018 Graves' guidelines
TYPICAL RESULT
Thyroid levels usually improve over several weeks.
SAFETY
Risks, side effects and who should avoid it
Rare but serious agranulocytosis: stop and get a blood count for fever or sore throat. Rash and liver injury can occur. In early pregnancy, PTU is preferred because of birth defect risk.
This summary is not a complete list of risks. Read the official prescribing information and discuss your own history with your clinician.
KEY REFERENCE
Ross DS, et al. 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism. Thyroid. 2016
Educational content only, reviewed by Farhan Tahir, MD. Not individual medical advice. Medicines named here require a prescription and medical supervision.