Easy-to-read medicine information about carbimazole – what is it, how to take carbimazole safely and possible side effects.

Type of medicine Also called
  • Anti-thyroid medicine
  • Neo-Mercazole®

What is carbimazole?

  • Carbimazole is used to control an overactive thyroid gland (hyperthyroidism). 
  • It stops your thyroid gland from making too much thyroid hormone (thyroxine or triiodothyronine).


  • Treatment with carbimazole is started at high doses (15 to 40 milligrams per day) for 4 to 8 weeks, until your thyroid returns to normal activity. The dose is then slowly reduced so that your thyroid gland can maintain its normal activity.
  • Treatment with carbimzaole is usually continued for 12 to 18 months.

How to take carbimazole

  • Swallow your carbimazole tablets whole with a glass of water.
  • Try taking your carbimazole tablets at the same times each day. 
  • You can take carbimazole with or without food. 
  • If you forget to take your dose, take it as soon as you remember. But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
  • Keep taking your carbimazole tablets. It may take 4 to 8 weeks before you notice an improvement.  

Possible side effects

Like all medicines, carbimazole can cause unwanted side effects, although not everyone gets them. Often unwanted effects improve as your body gets used to the new medicine.  

Side effects What should I do?
  • itchy skin rash
  • pain in your joints, bones and muscles
  • stomach upset
  • nausea (feeling sick) 
  • These are quite common when you first start carbimazole, and settle after a few weeks
  • Let your doctor know if troublesome 
  • In rare cases carbimazole can cause a sudden drop in your white cells putting you at risk of picking up infections
  • Signs of an infection such as fever, chills, feeling tired, sore throat, sores in the mouth or on the skin, feeling unwell (like you're getting the flu)
  • Tell your doctor immediately or ring HealthLine 0800 611 116
  • Signs of problems with your liver such as yellowing of the skin or eyes, dark urine, pain in the tummy (abdomen)
  • Tell your doctor immediately or ring HealthLine 0800 611 116


Carbimazole can interact with a few medications and herbal supplements, so check with your doctor or pharmacist

Learn more

Neo-Mercazole Medsafe Consumer Information Sheet 

Credits: Sandra Ponen, Pharmacist.