What it is used for
- Overactive thyroid (hyperthyroidism), including Graves' disease
- Preparing for thyroid surgery or radioactive iodine treatment
How it works
It reduces how much thyroid hormone the overactive thyroid gland produces, helping bring high hormone levels back toward normal.
How it is taken
Taken as a tablet, usually once or several times a day depending on the plan, and converted in the body to its active form (methimazole). Take it exactly as your doctor directs, attend regular blood tests, and do not stop without advice.
No doses here on purpose. The right strength and schedule depend on you — only a doctor or pharmacist should set them. Always follow your prescription and the label.
Common side effects
- Nausea
- Headache
- Mild stomach upset
- Skin rash or itching
- Joint aches
- Altered taste
Serious effects — get help
- Sore throat, mouth ulcers, fever, or signs of infection (possible serious drop in white blood cells, needs urgent blood test)
- Yellowing of the skin or eyes or severe abdominal pain (liver problems)
- Unusual bruising or bleeding
- Signs of a severe allergic reaction
If a reaction is severe — for example trouble breathing, swelling of the face or throat, or collapse — go to the nearest emergency room now or call your local emergency number. Do not wait for an online consultation.
Interactions to watch
- Other medicines affecting the thyroid or blood counts
- Blood-thinning medicines may need monitoring
- Tell your clinician about all medicines, including those for the heart
Who should take care
- Report any sore throat, fever, or infection symptoms straight away and stop until you have had a blood test, as advised
- Dose and choice of antithyroid drug may change in pregnancy, so tell your clinician if you are or could be pregnant
- Regular blood tests are needed to monitor thyroid levels and blood counts
- Tell your clinician about any liver problems