Thyroid hormone plays an important role in our body’s metabolism, growth and development. However, an excessive level of thyroid hormone might bring harmful effects to our body. Carbimazole is a common medication used to treat overactive thyroid glands (hyperthyroidism). It works by reducing the level of thyroid hormone in our body. In this article, we will look into detail on what carbimazole does to the body.

What is hyperthyroidism?

Hyperthyroidism is a condition in which your thyroid gland produces excessive thyroid hormone. It will accelerate your body’s metabolism, leading to symptoms such as rapid heart rate, weight loss, anxiety, tiredness and heat intolerance.

Several complications might develop if the condition is not treated in time. Below are the potential complications of hyperthyroidism:

  • Thyroid eye disease
    • Bulging eyes are the characteristic feature of thyroid eye disease which might lead to dry and gritty eyes, blurred vision or double vision.
  • Heart problem
    • Excessive thyroid hormone might cause your heart to beat irregularly with a fast heart rate. In the long run, your heart might fail due to overworking.
  • Weakened bone (osteoporosis)
    • Thyroid hormone might speed up the process of bone erosion, leading to weakened and fragile bones.
  • Pregnancy problem
    • An uncontrolled hyperthyroidism is dangerous for pregnant mum and also the baby. It might lead to high blood pressure in the pregnant mum, miscarriage, premature labour and baby might born with low birthweight.
  • Thyroid storm
    • A life-threatening condition in which there is a sudden flare up of symptoms of hyperthyroidism.

What does Carbimazole do to the body?

Thyroperoxidase is the enzyme that couples iodine to thyroglobulin to form thyroid hormone. Carbimazole reduces the uptake of iodine by the thyroid gland and converts into a chemical known as methimazole which blocks the enzyme thyroperoxidase, hence lowering the level of thyroid hormone.


Carbimazole is an oral tablet which is required to be consumed daily for patients with hyperthyroidism. The dosage will be adjusted based on the individual’s condition and thyroid hormone level. It might take 1-2 months before symptoms are relieved and the thyroid hormone level returns back to normal. During treatment, the doctor might perform several blood tests to monitor thyroid hormone level and also the side effects. Compliance to the medication is important to control the condition and overall long-term health.


Carbimazole is used in treatment for confirmed cases of hyperthyroidism. It is also used to prepare patients going for thyroid removal surgery (thyroidectomy) aimed to normalise the level of thyroid hormone. Carbimazole is also used as a temporary treatment before patients undergo radio-iodine therapy.

Side effects

Side effects might be present within 8 weeks of starting treatment. The side effects are usually mild and might heal by itself. 

Listed below are the common side effects that patients might experience:

  • Dizziness
  • Headache
  • Joint pain
  • Stomach upset
  • Rashes
  • Itchy rash

Rare but serious side effects

Treatment with carbimazole should be stopped immediately if any of the side effects listed below are noted.

  • Bone marrow suppression- can cause a sudden drop in levels of red blood cells, white blood cells and platelets, which can make one vulnerable to infections. Patients should notify the doctor immediately if they experience fever, mouth ulcers, sore throats, bruising or bleeding.
  • Liver dysfunction- might present itself with loss of appetite, weight loss, pain in upper abdomen, whole body itchiness, or yellowing of skin or eyes.
  • Severe skin reaction due to hypersensitivity to carbimazole.
  • Inflammation of pancreas (Acute pancreatitis)


Carbimazole is one of the treatments for hyperthyroidism. It works by blocking the enzyme thyroperoxidase in the thyroid gland, hence reducing the level of thyroid hormone. However, in certain cases, it might bring serious side effects. It is important to notify your doctor if you experience any unpleasant side effects during your treatment.