Hyperthyroidism (overactive thyroid): symptoms, causes and treatment

The NHS says an overactive thyroid can cause a wide range of symptoms, although it is unlikely you will have all of them. They may develop gradually or suddenly, and for some people they are mild while for others they are severe and significantly affect life. The NHS lists symptoms and physical signs separately.

The thyroid is a small butterfly-shaped gland in the neck, just in front of the windpipe. The NHS says it produces hormones that affect things such as your heart rate and body temperature, and having too much of them can cause unpleasant and potentially serious problems that may need treatment. An overactive thyroid is also known as hyperthyroidism or thyrotoxicosis.

The NHS says an overactive thyroid is usually treatable and that you will usually be referred to a hormone specialist (endocrinologist) who will plan treatment. Each treatment has benefits and drawbacks.

The NHS says that during the first couple of months some people get side effects of thionamides such as feeling sick, high temperature, headaches, aching joints, altered taste, upset stomach or an itchy rash, which should pass. A less common but serious side effect is a sudden drop in white blood cells (agranulocytosis), which can make you very vulnerable to infections. Contact your doctor immediately if you get symptoms such as a high temperature, sore throat or a persistent cough.

After radioactive iodine treatment the NHS says to avoid prolonged close contact with children and pregnant women for about 3 weeks, women should avoid getting pregnant for at least 6 months, and men should not father a child for at least 4 months.

The NHS says there are several reasons the thyroid can become overactive:

• Graves' disease: an autoimmune condition where the immune system produces antibodies that cause the thyroid to make too much hormone. About 4 in every 5 people with an overactive thyroid have it.

• Lumps (nodules) on the thyroid, where the extra thyroid tissue produces hormones.

• Some medicines, such as amiodarone, which can be used to treat an irregular heartbeat.

The NHS says to see a GP if you think you may have an overactive thyroid. Diagnosis is based on your symptoms and a blood test that assesses how well the thyroid is working. A thyroid function test checks levels of thyroid-stimulating hormone (TSH), triiodothyronine (T3) and thyroxine (T4). A low level of TSH and high levels of T3 and/or T4 usually means you have an overactive thyroid.

If levels are high, you may be referred to a specialist for further tests to find the cause, such as a blood test for anti-thyroid antibodies (usually found with Graves' disease), an ESR test to check for inflammation (a sign of thyroiditis), or a thyroid scan to look for nodules.

The NHS says it is very important to use contraception if you are taking carbimazole or have had radioactive iodine treatment in the last 6 months, because both can harm an unborn baby. Tell your doctor immediately if you are planning a pregnancy or become pregnant while taking carbimazole or within 6 months of radioactive iodine.

If you have an overactive thyroid during pregnancy and it is not well controlled, the NHS says it can increase the risk of pre-eclampsia, miscarriage, premature labour and birth, and low birthweight. Your doctor will check that your condition is under control, and if you take carbimazole they may recommend switching to propylthiouracil, which will not affect your baby.

The NHS lists eye problems (thyroid eye disease), which affect around 1 in 4 people with an overactive thyroid caused by Graves' disease, an underactive thyroid after radioactive iodine, pregnancy problems and, rarely, a thyroid storm. It also says an overactive thyroid can increase the chance of atrial fibrillation, weakened bones (osteoporosis) and heart failure.

A thyroid storm is a sudden flare-up of symptoms that can be triggered by an infection, pregnancy, not taking your medicine correctly or damage to the thyroid. Symptoms include a rapid heartbeat, high temperature, high blood pressure, jaundice, severe agitation and confusion, and loss of consciousness. The NHS says it is a medical emergency and to call 999 to ask for an ambulance immediately.

On the NHS, a GP can arrange the thyroid blood test and refer you to an endocrinologist for treatment planning. The three main treatments are the same in private care; the main differences are waiting times and cost.

If you have private tests, share the results with your GP. If you are planning a pregnancy, tell your doctor early, because the choice of treatment can change.