How does carbimazole work?
When you have an overactive thyroid, also known as hyperthyroidism or thyrotoxicosis, your thyroid gland produces too much of the thyroid hormones. When these hormone levels are too high, you can have mood swings and weight loss.
Your thyroid gland uses a chemical called iodine to produce these hormones. Carbimazole blocks the way your body processes iodine and reduces the amount of thyroid hormones produced. This can then help your symptoms.
When will I feel better?
Carbimazole starts working straight away. You may start to feel better after 1 to 3 weeks but it can take 1 to 2 months before the medicine works fully.
Are there any long-term side effects?
Carbimazole is generally safe to take for a long time, even many years.
It's important to have regular blood tests during treatment, to make sure your dose is not too high or too low. Your doctor will make sure you're on the lowest dose that works for you.
Your doctor will be able to explain the risks and benefits of taking carbimazole, compared with the risks of not having treatment for your overactive thyroid.
Are there other medicines for an overactive thyroid?
The main treatments for an overactive thyroid are:
- medicines such as carbimazole and propylthiouracil
- a combination of medicines such as carbimazole (for overactive thyroid) and levothyroxine (for underactive thyroid) to help find the right hormone balance (block and replace regimen)
- radioactive iodine treatment
- surgery
You will usually be referred to a specialist in hormonal conditions (endocrinologist). They will be able to help you manage your condition and discuss the best treatment option for you.
Do I need to avoid people with viruses while I'm taking it?
Generally, there is no problem with being around other people, including someone with a virus, when taking carbimazole.
However, there's one uncommon side effect with carbimazole, which may lower the number of white cells in your blood. This can make you more likely to get an infection.
Tell your doctor if you think you are getting a sore throat or if you have a high temperature.
Will it make me lose or put on weight?
One of the symptoms of an overactive thyroid is weight loss. Once you start taking carbimazole, you will stop losing weight as your hormone levels stabilise.
Once you are on the right dose of carbimazole, and your thyroid hormone levels have returned to normal, the treatment will no longer affect your weight.
Do I need to stop taking carbimazole before surgery or before tests?
No, carry on taking carbimazole, following the instructions that come with your medicine.
However, if you're having radioactive iodine treatment, your doctor may tell you to stop taking carbimazole for a while.
If you need to make any changes, a doctor will talk to you about it before the surgery.
Will it affect my contraception?
It's important to use reliable contraception while taking carbimazole. You can discuss contraception with your doctor, sexual health or family planning clinic.
Carbimazole will not affect any contraception, including the combined pill, progestogen-only pill and emergency contraception.
If carbimazole make you sick (vomit), your contraceptive pills may not protect you from pregnancy. Look at the leaflet that comes with your contraceptive pills to find out what to do.
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Can I drive or ride a bike?
For most people, carbimazole does not affect their ability to drive or ride a bike.
However if carbimazole makes you feel dizzy, do not drive a car, cycle, use tools or operate machinery until you feel OK again.
It's an offence to drive a car if your ability to drive safely is affected. It's your responsibility to decide if it's safe to drive. If you're in any doubt, do not drive.
Talk to your doctor or pharmacist if you're unsure whether it's safe for you to drive while taking carbimazole. GOV.UK has more information on the law on drugs and driving.
Can I drink alcohol while taking carbimazole?
Yes, you can drink alcohol while taking carbimazole. Alcohol does not affect how this medicine works.
However, if carbimazole makes you feel dizzy then it's best to stop drinking alcohol as it can make this side effect worse.
Is there any food or drink I need to avoid?
Carbimazole is not usually affected by what you eat or drink.
However, to keep your thyroid healthy, your doctor may suggest a low iodine diet. This is because the thyroid gland needs iodine to make the thyroid hormones. Eating foods that are high in iodine can make your symptoms worse.
Your doctor may recommend avoiding processed foods, cheese, eggs and salt with added iodine (iodised salt).
If carbimazole makes you feel dizzy, it's best to avoid alcohol, coffee and other drinks containing caffeine as these can also make the dizziness worse.
Can lifestyle changes help an overactive thyroid?
In addition to taking carbimazole, there are some lifestyle changes that can help with your symptoms. These include weight management, exercise and dealing with stress.
Taking carbimazole will stop the weight loss caused by an overactive thyroid. Your doctor may give you a meal plan to help you gain or lose weight while taking this medicine.
They may also recommend a low iodine diet. This is because the thyroid gland needs iodine to make thyroid hormones. Eating foods that are high in iodine can make your symptoms worse. This may mean avoiding processed foods, cheese, eggs and salt with added iodine (iodised salt).
Regular exercise and managing stress can help with other symptoms such as anxiety, irritability, difficulty sleeping and hyperactivity.