Overactive thyroid (hyperthyroidism) means your thyroid gland is releasing too much thyroid hormone. This speeds up your body's metabolism, leading to symptoms such as shaking, weight loss and anxiety.
If you have overactive thyroid it means your thyroid gland is producing too much thyroid hormone.
Your thyroid gland is in your neck, in front of your windpipe. It releases two hormones to control how quickly your body uses its energy stores and how sensitive your body is to other hormones. The two main hormones are known as thyroxine (T4) and triiodothyronine (T3).
In the UK, about one in 100 people have overactive thyroid and it’s about six times more common in women than men.
Symptoms of overactive thyroid can include:
These symptoms aren’t always caused by overactive thyroid but if you have them it’s best to see your GP.
If left untreated, overactive thyroid can increase your risk of heart failure. You may also develop problems with your vision. Rarely, you may develop a life-threatening reaction called a thyroid storm (thyrotoxic crisis). The symptoms of a thyroid storm include having a very fast heart beat, fever and jaundice. This is where your skin and the whites of your eyes appear yellow in colour.
If you’re a woman, having an overactive thyroid can increase your risk of:
If you become pregnant, having overactive thyroid may increase your risk of having a miscarriage, premature birth or a baby with low birth weight.
The most common causes of overactive thyroid are described below.
Your GP will ask about your symptoms and examine you, and may ask you about your medical history. They may also ask if you have a family history of autoimmune disease or thyroid disease.
Your GP may take a blood sample. Often, the blood test begins by measuring your levels of thyroid stimulating hormone (TSH). TSH is made in the pituitary gland in your brain and controls the production of thyroxine and triiodothyronine.
If your thyroid gland is overactive, your level of TSH will be low. If this is shown in your blood test, your thyroid hormone levels will also be measured.
If blood tests show high levels of either T4 or T3 (or both) and a low level of TSH , this confirms an overactive thyroid. Your GP will either advise you about your treatment options or refer you to an endocrinologist (a specialist in identifying and treating thyroid conditions).
You may need to have a radioisotope scan. This involves having a small amount of a radioactive substance injected into your blood, which is taken up by your thyroid gland. Scans of your thyroid gland will show up any overactive areas.
Treatment aims to return your levels of thyroid hormones to normal.
Your doctor may prescribe you antithyroid medicines (either carbimazole or propylthiouracil) to reduce the production of thyroid hormone in your thyroid gland. You will need to take these medicines for 12 to 18 months. These medicines can sometimes lead to an underactive thyroid (hypothyroidism), so you will need regular blood tests to check your levels of thyroid hormones.
Your doctor may also prescribe you beta-blockers, such as propranolol, to help manage the symptoms of overactive thyroid until your hormone levels return to normal. If you have asthma, you should never take a beta-blocker as this can make your asthma worse. Your doctor may instead offer you calcium-channel blockers, such as verapamil or diltiazem, to slow down a fast heart rate caused by an overactive thyroid. These medicines are usually only prescribed if you’re having symptoms or during a thyroid storm.
Beta blockers (or calcium channel blockers) don’t treat the underlying problem. But they should protect your heart from high levels of thyroid hormone while other treatments lower your thyroid hormone levels back to normal.
When you’re diagnosed with hyperthyroidism and receiving treatment, you’ll need regular blood tests. This helps manage your condition and ensures you’re receiving the right dosage of antithyroid medicines. Thyroid function tests measure levels of thyroid-stimulating hormones (TSH) in your blood and may include tests of T4 and T3 levels. Your blood tests will usually be:
Be aware that results from different labs can vary so aren’t always comparable. Plus, there are different ranges used if you’re pregnant. If you have a specific query about your blood test results and what they mean, speak to your doctor.
If antithyroid medicines aren’t effective for you, then your doctor might suggest radioiodine treatment. This involves taking iodine as a tablet or drink, which is taken up by your thyroid gland. As the radioactivity builds up, it destroys some of your thyroid tissue, so the gland produces less thyroid hormones. Usually, you will be given a single dose of radioiodine sufficient to stop all your thyroid activity. If radioiodine treatment successfully reduces the activity of your thyroid gland, you will need to take levothyroxine every day for the rest of your life. Levothyroxine is a thyroid hormone replacement medicine.
Radioiodine treatment is usually offered as an alternative to surgery when antithyroid medicines aren’t suitable or are ineffective. However, radioactive iodine isn’t suitable if you’re pregnant or breastfeeding. It also isn’t practical if you have young children to care for because your contact with them will be restricted for four weeks after receiving radioactive iodine.
Your doctor may suggest having an operation to remove all or part of your thyroid gland (called a thyroidectomy). Before surgery, your thyroid hormone levels will need to be controlled. This is because an overactive thyroid can increase your risk of complications when you have a general anaesthetic.
After surgery, you may need to take levothyroxine every day for the rest of your life. Surgery is offered as an alternative to medicines and radioactive iodine when they are either ineffective or not practical. Surgery may also be a good option if you need a more immediate response to treatment. This is because surgery is immediately effective. Radioactive iodine can take up to 12 months to take effect and doesn’t work every time. If you need more information, speak to your doctor.
Reviewed by Alice Rossiter, Bupa Health Information Team, May 2014.
For answers to frequently asked questions on this topic, see FAQs.
For sources and links to further information, see Resources.
This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.
Get checked out with Bupa Health Assessments
Choose from our extensive range of health assessments to identify any health issues and help you take positive steps to put them right.
Bupa Health Finder
Find health information and more while on the move with our free Bupa Health Finder app.