Carbimazole for hyperthyroidism

node leader
Share this page: 

Carbimazole for hyperthyroidism

This leaflet is about the use of carbimazole for hyperthyroidism (overactive thyroid gland).

Information-Standard-logoThis leaflet has been written for parents and carers about how to use this medicine in children. Our information sometimes differs from that provided by the manufacturers, because their information is usually aimed at adult patients. Please read this leaflet carefully. Keep it somewhere safe so that you can read it again.

Name of drug


Why is it important for my child to take this medicine?

Hyperthyroidism means that the thyroid gland is overactive and makes too much thyroid hormone. Thyroid hormone helps to control energy levels and growth. Too much thyroid hormone can make it difficult for your child to gain weight and grow well, and may make them feel tired and anxious. Carbimazole works by decreasing the amount of thyroid hormone released from the thyroid gland.

What is carbimazole available as?

  • Tablets: 5 mg, 20 mg; these may contain lactose.

If you have any concerns or questions, speak with your child's doctor or pharmacist.

When should I give carbimazole?

Carbimazole may be given once, twice or three times each day. Your doctor will tell you how often to give it.

  • Once a day: this can be in the morning OR the evening.
  • Twice a day: this should be once in the morning and once in the evening. Ideally, these times are 10–12 hours apart, for example some time between 7 and 8 am, and between 7 and 8 pm.
  • Three times each day: this should be once in the morning, once in the early afternoon and once in the evening. Ideally, these times are at least 6 hours apart, for example 8 am, 2 pm and 8 pm.

Give the medicine at about the same time each day so that this becomes part of your child’s daily routine, which will help you to remember.

How much should I give?

Your doctor will work out the amount of carbimazole (the dose) that is right for your child. The dose will be shown on the medicine label.

Your doctor may suggest that your child has a low dose to start with. They may then increase the dose as your child gets used to the medicine and depending on how your child responds to it.

It is important that you follow your doctor’s instructions about how much to give.

How should I give it?

This medicine works best when the stomach is empty, so try to give it to your child about an hour before they eat. However, if your child has an upset stomach, you can give it with a small amount of food.

Tablets should be swallowed with a glass of water, milk or juice. Your child should not chew the tablet. You can crush the tablet and mix it with a small amount of water. Make sure your child swallows it straight away.

When should the medicine start working?

The medicine will start to work within 1–2 hours but it may be several weeks before your child’s symptoms start to improve. However, you may not see much difference in your child if they didn’t have any obvious symptoms of hyperthyroidism. Continue to give the medicine to your child during this time. If you are worried about whether it is helping, contact your doctor.

What if my child is sick (vomits)?

  • If your child is sick less than 30 minutes after having a dose of carbimazole, give them the same dose again. 
  • If your child is sick more than 30 minutes after having a dose of carbimazole you do not need to give them another dose. Wait until the next normal dose.

If your child is sick again, seek advice from your GP, pharmacist or hospital. They will decide what to do based on your child’s condition and the specific medicine involved.

What if I forget to give it?

  • If you usually give it once a day in the morning: Give the missed dose when you remember during the day, as long as this is at least 12 hours before the next dose is due. 
  • If you usually give it once a day in the evening: If you remember before bedtime, give the missed dose. You do not need to wake up a sleeping child to give a missed dose. You can give the missed dose in the morning, as long as this is at least 12 hours before the evening dose is due.
  • If you usually give it twice a day: If you remember up to 4 hours after you should have given a dose, give your child the missed dose. For example, if you usually give a dose at about 7 am, you can give the missed dose at any time up to 11 am. If you remember after that time, do not give the missed dose. Just give the next dose as usual.
  • If you usually give it three/four times a day: Do not give the missed dose. Just give the next dose as usual.

What if I give too much?

You are unlikely to do harm if you give an extra dose of carbimazole by mistake. If you are concerned that you may have given too much, contact your doctor or local NHS services (111 in England and Scotland; 0845 4647 in Wales). Have the medicine or packaging with you if you telephone for advice.

Are there any possible side-effects?

We use medicines to make our children better, but sometimes they have other effects that we don’t want (side-effects).

Side-effects that you must do something about

If your child is short of breath or is wheezing, or their face, lips or tongue start to swell, or they develop a rash, they may be allergic to carbimazole. Take your child to hospital or call an ambulance straight away.

If your child develops a fever (temperature above 38°C), sore throat or mouth ulcers, or unusual bruising or bleeding, or feels unusually tired, contact your doctor straight away.

If your child has muscle pains or you notice yellowing of their skin or eyes, contact your doctor.

Other side-effects you need to know about

Your child may get some of the following side effects with carbimazole. Any side-effects that do occur are likely to be mild and wear off after a week or so. If they are still a problem after 2 weeks, or you are worried, contact your doctor but continue to give carbimazole.

  • Your child may feel sick (nausea) or have symptoms of mild stomach upset. Giving the medicine with some food or milk may help. 
  • Headache, or painful joints – it is safe to give ibuprofen and/or paracetamol.
  • Changes in taste – eating citrus fruits (e.g. oranges), taking sips of water or sucking on sugar-free boiled sweets may help.
  • Your child may develop itchiness or a mild skin rash – try applying a moisturising cream or itch relief cream. If this doesn’t help, contact your doctor, in case your child is allergic to carbimazole.
  • Your child’s hair may become thinner and some may fall out. If this happens, discuss it with your doctor at your next visit..

These effects usually occur within the first 8 weeks of treatment and tend to improve with time.

There may, sometimes, be other side-effects that are not listed above. If you notice anything unusual and are concerned, contact your doctor. You can report any suspected side-effects to a UK safety scheme at http://www.mhra.gov.uk/yellowcard.

More information on side-effects can be found in the following leaflet http://www.medicinesforchildren.org.uk/side-effects-childrens-medicines

Can other medicines be given at the same time as carbimazole?

  • You can give your child medicines that contain paracetamol or ibuprofen, unless your doctor has told you not to.
  • Carbimazole should not be taken with some medicines that you get on prescription. Tell your doctor and pharmacist about any other medicines your child is taking before giving carbimazole.
  • Check with your doctor or pharmacist before giving any other medicines to your child. This includes herbal or complementary medicines.

Is there anything else I need to know about carbimazole?

Your doctor will test your child’s blood regularly, to measure the levels of thyroid hormone and make sure that your child is on the right dose of carbimazole.

If your daughter thinks that she may be pregnant, it is important that she sees her doctor as soon as possible. She should keep taking her medicine until she sees her doctor.

General advice about medicines

  • Try to give medicines at about the same times each day, to help you remember. 
  • If you are not sure a medicine is working, contact your doctor but continue to give the medicine as usual in the meantime. Do not give extra doses, as you may do harm.
  • Only give this medicine to your child. Never give it to anyone else, even if their condition appears to be the same, as this could do harm. 
  • If you think someone else may have taken the medicine by accident, contact your doctor for advice.
  • Make sure that the medicine you have at home has not reached the ‘best before’ or ‘use by’ date on the packaging. Give old medicines to your pharmacist to dispose of.

Where should I keep this medicine?

  • Keep the medicine in a cupboard, away from heat and direct sunlight. It does not need to be kept in the fridge.
  • Make sure that children cannot see or reach the medicine.
  • Keep the medicine in the container it came in.

Who to contact for more information

Your child’s doctor, pharmacist or nurse will be able to give you more information about carbimazole and about other medicines used to treat hyperthyroidism.

You can also get useful information from: 
Publication date: