Carbimazole Dosage Guide: How Much to Take and What to Watch For

When your thyroid goes into overdrive, carbimazole, a thionamide drug used to treat overactive thyroid conditions like Graves’ disease. Also known as neo-Mercazole, it works by blocking the production of excess thyroid hormones. It’s not a cure, but it’s one of the most common first-line treatments for hyperthyroidism, a condition where the thyroid gland makes too much hormone, leading to weight loss, rapid heartbeat, and anxiety. Many people start on carbimazole after a blood test shows high T3 and T4 levels, and it’s often the go-to choice because it’s effective, affordable, and well-studied.

There’s no one-size-fits-all dose. Most adults begin with 10 to 30 mg per day, split into one or two doses. If your thyroid is really overactive, your doctor might start you higher—up to 40 mg daily. After 4 to 8 weeks, they’ll check your thyroid levels again and lower the dose to a maintenance level, usually 5 to 15 mg a day. Some people stay on low doses for months or even years. Kids and older adults often get lower doses, and pregnant women need careful monitoring because carbimazole can cross the placenta. It’s not the same as methimazole, a similar drug used more often in the U.S., with slightly different dosing and side effect profiles. In the UK and many other countries, carbimazole is preferred over methimazole simply because it’s been the standard for decades.

Side effects are usually mild—itchy skin, nausea, joint pain—but you need to watch for rare but serious ones like low white blood cell counts (agranulocytosis), which can cause fever or sore throat. If you get those, stop taking it and get blood work done right away. Most people tolerate carbimazole fine, especially once the dose is lowered. It’s not a quick fix; it takes weeks to feel better. And it’s not the only option—radioactive iodine or surgery are alternatives, but carbimazole lets you try a non-invasive route first.

Below you’ll find real-world comparisons, dosage charts, and insights from people who’ve used carbimazole for thyroid issues. You’ll see how it stacks up against other treatments, what doctors actually recommend in practice, and how to manage the day-to-day stuff—like missed doses, drug interactions, and when to push back if you’re not feeling right. This isn’t theory. It’s what works for real patients.