Carbimazole

Carbimazole is suitable for most adults and children, but always check before taking it.

Carbimazole is not suitable for some people. For example, check with your doctor if you have liver problems or cannot have regular blood tests.

Carbimazole comes as tablets that you take 2 to 3 times a day. Follow the instructions that come with your medicine.

Side effects of carbimazole include headaches and feeling sick. More serious side effects can happen in rare cases.

Most adults (aged 18 years old and over), children and babies can take carbimazole.

Carbimazole is not suitable for some people. To make sure it's safe for you, tell your doctor or pharmacist if you:

• have ever had an allergic reaction to carbimazole, other thyroid medicines like propylthiouracil or any other medicine
• have had severe pancreas problems (acute pancreatitis) after taking carbimazole in the past
• are receiving or are due to have radioactive iodine treatment for your overactive thyroid
• have liver problems
• have a problem with your blood
• have a swollen thyroid (goitre)
• cannot have regular blood tests
• are trying for a baby, pregnant or breastfeeding, or there's a chance you could get pregnant

Carbimazole comes as 5mg, 10mg, 15mg and 20mg tablets. You may need to take more than 1 tablet to make up your dose.

Doses vary depending on your symptoms, your thyroid hormone levels and whether you have any other health conditions. Your doctor will tell you how many tablets to take.

The usual starting dose for adults is between 20mg and 60mg a day.

When you first start taking carbimazole, you will take it 2 or 3 times a day. Try to space the doses evenly throughout the day. If you take it 3 times a day, you could take it first thing in the morning, in the middle of the afternoon and at bedtime.

The starting dose for children depends on their age and weight. Children may take it once a day, or divided into 2 or 3 smaller doses.

How to take it

Swallow the tablets whole, with a drink of water.

You can take carbimazole with or without food.

Side effects usually improve as your body gets used to carbimazole. There are things you can do to help cope with them:

Stick to simple meals and try not to eat rich or spicy food. It may help to take your carbimazole with food or just after eating to avoid feeling sick.

If you're being sick, try small frequent sips of water to avoid dehydration. Signs of dehydration include peeing less than usual or having strong-smelling pee.

Contact a doctor if feeling or being sick lasts for more than a few days.

Tell your doctor if you are vomiting due to a stomach bug or illness that lasts for more than 2 days.

If you take the combined pill or progestogen-only pill and you're being sick, your contraception may not protect you from pregnancy. Check the pill packet for advice.

Lie down until the dizziness passes, then get up slowly. Move slowly and carefully. Avoid coffee, cigarettes, alcohol and recreational drugs. Do not drive, cycle or operate machinery until you feel OK again.

If the dizziness does not get better, or this keeps happening, speak to a doctor.

Make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Ask your pharmacist to recommend a painkiller.

Headaches should usually go away. Talk to your doctor if they do not go away or are severe.

Cooling treatments can help with joint pain. Try putting an ice pack wrapped in a cloth on the joint for about 15 to 20 minutes, and repeat several times a day. Avoid keeping the joint still and take gentle exercise to stop it becoming stiff. Ask a pharmacist to recommend a painkiller.

Speak to your doctor if the pain does not go away or is severe.

Use unperfumed moisturiser or skin lotion, wear loose cotton clothing, keep your nails clean, short and smooth, and pat or tap the skin instead of scratching it. Ask your pharmacist to recommend an antihistamine.

No one knows if taking carbimazole causes this or if it's the changes in your thyroid hormone levels. Hair usually grows back, but this may take a little while because the natural cycle of hair growth takes several months.

Talk to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.

It's important to correctly treat a thyroid problem in pregnancy. If your thyroid hormone levels are too high or too low, this can cause problems for your baby.

Carbimazole is not often recommended during pregnancy. You'll usually be switched to another thyroid medicine called propylthiouracil (PTU).

This is because carbimazole can very occasionally cause problems for your baby's development in early pregnancy. However, not everyone can take PTU and in some cases, continuing carbimazole may be the safest option.

If you become pregnant while taking carbimazole, keep taking it and speak to your doctor as soon as possible. You will be invited to see a pregnancy specialist (obstetrician) and a hormone specialist (endocrinologist). They can advise you on the best treatment options for you and your baby.

If you continue taking carbimazole in pregnancy, you'll need regular blood tests to check you're on the right dose. You may also have extra scans to check the health of your growing baby.

If your baby is healthy, it's usually OK to take carbimazole while you are breastfeeding, and it's important to treat your thyroid problem.

Carbimazole gets into breast milk in small amounts. It's unlikely to cause any side effects in your baby or affect their thyroid hormones.

It's very rare for breastfed babies to have side effects from medicines you're taking. But it's important to keep monitoring your baby if you're taking any medicine while breastfeeding.

Contact your healthcare professional or call 111 as soon as possible if you notice that your baby:

• is not feeding as well as usual or not putting on weight as you would expect
• is unusually sleepy or irritable
• has a rash
• has difficulty pooing (constipation)
• gets infections regularly

Your doctor may take a blood test from your baby to check everything is OK.

If your baby has any symptoms that are not listed, or if you're worried about them, you can also call 111 or contact any healthcare professional.

Carry on taking the medicine, and keep breastfeeding as usual until you've got advice about your baby's symptoms.

Taking carbimazole can affect the way certain medicines work, while some medicines are affected by your thyroid hormone levels. These levels will change as carbimazole starts to work.

For this reason, your doctor will want to review the medicines you take and possibly change the dosage.

Tell your doctor before starting treatment with carbimazole if you take any other medicines, including:

• digoxin, a heart medicine
• erythromycin, an antibiotic
• theophylline, used to treat breathing problems
• bladder medicines for urinary incontinence and other bladder problems
• blood pressure medicines called beta blockers – these are often prescribed together with carbimazole and your doctor will tell you how much to take
• medicines that help prevent blood clots (anticoagulants) such as warfarin
• steroids such as prednisolone
• clozapine, an antipsychotic

These are not all the medicines that may cause problems if you take them with carbimazole. For a full list, see the leaflet inside your medicine packet.