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This is an information resource — not medical advice.

PillCodex provides general educational information about medications. This content is not a substitute for professional medical advice, diagnosis, or treatment. Never start, stop, or change a medication based on what you read here. Always speak to your doctor, pharmacist, or qualified healthcare provider with questions about your medications.

🚨 If you are experiencing a medical emergency or think you may have taken too much of a medication, call emergency services (911 in the US) or go to your nearest emergency room immediately.

Antithyroid Agent🔒 Prescription only

What Is Carbimazole Used For?

Brand names: Neo-Mercazole

Carbimazole is the main medication used to treat hyperthyroidism (overactive thyroid) and Graves' disease by reducing the amount of thyroid hormone the thyroid gland produces.

What is Carbimazole used for?

  • Hyperthyroidism (overactive thyroid)
  • Graves' disease
  • Toxic nodular goitre
  • Preparing for thyroid surgery or radioactive iodine treatment
  • Long-term management of mild hyperthyroidism

How does Carbimazole work?

Carbimazole is converted in the body to methimazole, which blocks the enzyme thyroperoxidase — the enzyme the thyroid needs to produce thyroid hormone. By blocking this enzyme, thyroid hormone production falls over several weeks.

Dosage information

💊Available forms
  • 5mg tablets
  • 20mg tablets
📏Typical dosage

Usually 15–40mg daily in divided doses when starting, reduced to 5–15mg daily as thyroid levels normalise. Takes 4–8 weeks to see significant effect.

⚠️ Dosage varies by individual. Always follow your doctor's or pharmacist's instructions — never self-dose based on general information.

Side effects

Common

  • Rash and itching
  • Nausea
  • Headache
  • Joint pain
  • Hair thinning

⚠️ Serious — contact your doctor

  • Agranulocytosis — dramatic fall in white blood cells causing life-threatening infection risk (STOP IMMEDIATELY and seek urgent care for fever, sore throat, or mouth ulcers)
  • Liver damage (rare)
  • Vasculitis (rare)

Important warnings

⚠️ URGENT: If you develop a fever, sore throat, or mouth ulcers while taking carbimazole, STOP the medication immediately and go to A&E/ER — this may indicate agranulocytosis, a potentially fatal blood disorder
Do NOT take during first trimester of pregnancy (different drug — propylthiouracil — used instead)
Regular thyroid function tests are required to adjust dose
Carry a warning card explaining the agranulocytosis risk

Drug interactions

These substances may interact with Carbimazole. This is not a complete list — always tell your doctor and pharmacist ALL medications and supplements you take.

Warfarin (thyroid levels affect warfarin dose needs)TheophyllineBeta-blockers (dose adjustments needed as thyroid normalises)Digoxin (dose adjustments needed)

Pregnancy & breastfeeding

🤰 Avoid in first trimester — specialist management required throughout pregnancy

Always consult your doctor or obstetrician before taking any medication during pregnancy or while breastfeeding.

Frequently asked questions

What is carbimazole used for?

Carbimazole treats hyperthyroidism (overactive thyroid) and Graves' disease by blocking thyroid hormone production. It takes 4–8 weeks to work and is often used for 12–18 months.

What is agranulocytosis and why is it dangerous with carbimazole?

Agranulocytosis is a sudden severe drop in white blood cells, leaving the body unable to fight infection. It occurs in about 0.1–0.5% of carbimazole users. Symptoms — fever, sore throat, mouth ulcers — require immediate emergency care. Never dismiss these symptoms while on carbimazole.

How long do I need to take carbimazole?

A course typically lasts 12–18 months. After stopping, about 50% of Graves' disease patients remain in remission. Others may need to restart, or choose radioactive iodine or surgery as a more permanent solution.

Can I take carbimazole during pregnancy?

Carbimazole is avoided in the first trimester due to a small risk of birth defects. Propylthiouracil (PTU) is used instead in early pregnancy. After the first trimester, carbimazole is generally used. This requires careful specialist management.

What are the symptoms of an overactive thyroid that carbimazole treats?

Hyperthyroidism causes rapid heartbeat, tremor, weight loss despite good appetite, heat intolerance, anxiety, sweating, and sometimes a swollen thyroid (goitre) or protruding eyes (in Graves' disease). Carbimazole gradually reverses these symptoms as hormone levels fall.

Related medications

💊LevothyroxineThyroid Hormone Replacement💊MetoprololBeta-Blocker💊PrednisoneCorticosteroid
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This is an information resource — not medical advice.

PillCodex provides general educational information about medications. This content is not a substitute for professional medical advice, diagnosis, or treatment. Never start, stop, or change a medication based on what you read here. Always speak to your doctor, pharmacist, or qualified healthcare provider with questions about your medications.

🚨 If you are experiencing a medical emergency or think you may have taken too much of a medication, call emergency services (911 in the US) or go to your nearest emergency room immediately.

Information on this page is sourced from general pharmaceutical references and is provided for educational purposes only. Drug information may change — always verify with your pharmacist or prescriber. PillCodex.com is not affiliated with any pharmaceutical company.