Generic Methimazole

Common use

Methimazole is an antithyroid medication used to treat hyperthyroidism, a condition where the thyroid gland produces excessive hormones. It is often prescribed for Graves’ disease, the most common cause of overactive thyroid. Methimazole works by inhibiting thyroid hormone synthesis, helping to restore normal thyroid levels. In some cases, it is used before surgery or radioactive iodine treatment.

Dosage and direction

The dosage of methimazole varies based on the severity of hyperthyroidism, typically starting at 5–30 mg daily divided into multiple doses. Once thyroid levels begin to normalize, the dose is usually reduced for maintenance. Tablets should be taken at the same time each day, with or without food. Follow your doctor’s instructions carefully and do not adjust the dose without medical advice.

Precautions

Before using methimazole, inform your doctor if you have liver disease, blood disorders, or a history of allergic reactions. Regular blood tests are necessary to monitor thyroid function and blood cell counts during treatment. Be alert for signs of infection, fever, or sore throat, as the drug may affect white blood cells. It is not typically recommended during the first trimester of pregnancy unless no alternatives are available.

Contraindications

Methimazole is contraindicated in individuals with a known hypersensitivity to the drug. It should not be used during the first trimester of pregnancy due to the risk of birth defects, unless specifically advised by a physician. Patients with serious blood disorders or preexisting liver problems should avoid methimazole. Always consult a healthcare provider before starting or stopping treatment.

Possible side effect

Common side effects include skin rash, nausea, headache, and joint pain. More serious but rare side effects include agranulocytosis (a dangerous drop in white blood cells), hepatitis, or vasculitis. Immediate medical attention is required if you experience symptoms like fever, sore throat, or unusual bruising. Most side effects are reversible if detected early.

Drug interaction

Methimazole may interact with blood thinners (like warfarin), beta-blockers, and theophylline, potentially requiring dose adjustments. It can also alter the effects of digoxin and other thyroid medications. Let your doctor know about all medications and supplements you're taking. Avoid iodine-containing supplements unless directed by a healthcare provider.

Missed dose

If you forget a dose, take it as soon as you remember. If it's nearly time for your next dose, skip the missed one—do not double the dose. Keep taking the medication consistently to maintain stable thyroid hormone levels. Setting a daily reminder can help prevent missed doses.

Overdose

An overdose may lead to hypothyroidism, with symptoms like fatigue, weight gain, or cold intolerance. Seek medical attention if you suspect an overdose. Treatment is usually supportive and based on symptoms. Never take more than the prescribed amount.

Storage

Store methimazole at room temperature (20°C to 25°C / 68°F to 77°F), away from light, moisture, and heat. Keep the medication in its original container and tightly closed. Keep out of reach of children and pets. Discard any unused or expired medication according to local guidelines.

Disclaimer

We provide only general information about medications which does not cover all directions, possible drug integrations, or precautions. Information at the site cannot be used for self-treatment and self-diagnosis. Any specific instructions for a particular patient should be agreed with your health care adviser or doctor in charge of the case. We disclaim reliability of this information and mistakes it could contain. We are not responsible for any direct, indirect, special or other indirect damage as a result of any use of the information on this site and also for consequences of self-treatment.

Clinical Verification

Last Clinically Updated: August 15, 2026

Written By

Dr. Elena Vance, PharmD

Clinical Specialist in Neuropharmacology

Fact Checked By

Marcus Thorne, MS

Biomedical Data & FDA Label Verification

Medically Reviewed By

Dr. Arthur Campbell, MD

Board-Certified Psychiatrist (ABPN)