If your doctor mentioned methimazole for an overactive thyroid, you probably want plain answers: why it’s used, what risks to expect, and how to stay safe. Methimazole is an antithyroid drug commonly prescribed for Graves' disease and other causes of hyperthyroidism. It slows thyroid hormone production so symptoms like racing heart, sweating, and anxiety calm down.
Methimazole blocks the thyroid’s ability to make T3 and T4 hormones. Doctors use it to control hyperthyroid symptoms before a more permanent treatment (like radioactive iodine or surgery), or to push the disease into remission. Typical starting doses vary with how severe the problem is—often between 10–40 mg daily—and doctors usually lower the dose once hormone levels improve. Your provider will check TSH and free T4 regularly to guide dosing changes.
Before starting, you’ll usually get baseline blood tests: thyroid tests, liver function tests, and sometimes a complete blood count (CBC). These help spot rare but serious reactions early.
Most people tolerate methimazole, but watch for a few things. Common side effects include mild stomach upset and a skin rash. Two issues deserve urgent attention: fever or sore throat (could signal agranulocytosis, a drop in white blood cells) and yellowing of the skin or dark urine (possible liver injury). If you get a fever, sore throat, mouth sores, or jaundice, stop the drug and contact your doctor or seek urgent care.
Monitoring is key. Many doctors check thyroid levels every 4–6 weeks when you start treatment, and repeat liver tests or CBC if symptoms appear. Don’t skip follow-up—early checks let your doctor reduce dose or switch therapy if needed.
Pregnancy and breastfeeding require extra caution. Methimazole is often avoided in the first trimester because of rare birth defect reports; propylthiouracil (PTU) is sometimes preferred early in pregnancy. If you’re pregnant, planning pregnancy, or breastfeeding, talk with your clinician about the safest option for you and your baby.
Practical tips: take methimazole at the same time each day, with or without food as your doctor advises. If you miss a dose, take it when you remember unless the next dose is imminent—don’t double up. Store the medicine at room temperature, out of reach of children.
Finally, methimazole requires a prescription. Be careful buying drugs online—use licensed pharmacies and keep your doctor in the loop. If you ever feel unsure about symptoms or tests, call your healthcare provider; catching problems early keeps treatment safe and effective.
