Overactive thyroid (hyperthyroidism)

Your health expert: Mr Robert Hardy, Consultant Surgeon and Dr Yasmin Rahman, Bupa Clinics GP
Content editor review by Dr Kristina Routh, Freelance Health Editor, December 2020.
Next review due December 2023.

If you have an overactive thyroid, it means your thyroid gland is making too much thyroid hormone. This is also known as hyperthyroidism or thyrotoxicosis.

Having an overactive thyroid can cause a wide range of symptoms. These may include feeling weak and tired, being anxious or irritable, and losing weight. Treatment can lower your thyroid hormone levels and usually ease your symptoms.

An image showing the location of the thyroid gland and surrounding structures

About overactive thyroid

Your thyroid gland is in your neck, in front of your windpipe. It produces two hormones called thyroxine (T4) and triiodothyronine (T3).

Thyroid hormones affect tissues throughout your body, helping to control your metabolism. Your metabolism is the combination of all the chemical processes that happen in your body including those that change the food you eat into energy. Too much thyroid hormone speeds up your body’s metabolism. When your metabolism speeds up, you may lose weight even though you’re eating more, and have other symptoms such as a fast heart rate.

If you’re a woman, you’re up to 10 times more likely to have an overactive thyroid than if you were a man.

Symptoms of overactive thyroid

Overactive thyroid symptoms can vary – you might just have mild symptoms or they may be severe. Your symptoms can depend on your age and on what’s causing your overactive thyroid. And how bad your symptoms are doesn’t always reflect how high your thyroid hormones are. For example, you may feel fairly well even if your thyroid hormones are quite high.

The main symptoms of overactive thyroid include:

  • feeling tired with weak muscles
  • feeling hot and less able to cope with heat
  • losing (or sometimes gaining) weight without intending to
  • feeling hungry and eating more than is usual for you
  • diarrhoea
  • sweating more than usual
  • feeling emotionally up and down, restless and irritable
  • a feeling of pressure in your neck or difficulty swallowing
  • a swelling or a lump in the front of your neck (this is called a goitre and can be caused by a large thyroid gland)
  • feeling anxious
  • shaking (tremors)
  • a fast or irregular heart rate (palpitations)
  • feeling breathless
  • losing your hair, which may become generally sparse (but usually grows back with treatment)
  • in women, irregular or no periods
  • in men, less interest in having sex (a reduced libido) and swollen breast tissue (gynaecomastia)

If you have any of these symptoms, contact your GP.

Some people with overactive thyroid get problems with their eyes. For more information about this, see our FAQ: Can an overactive thyroid gland cause eye problems?

Diagnosis of overactive thyroid

Your GP will ask about your symptoms and examine you. They may ask you about your medical history and if anyone in your family has an overactive thyroid gland.

If your GP thinks you may have an overactive thyroid, they’ll ask you to have one or more blood tests. This is to check the level of thyroid hormones in your body. The main hormones measured in blood tests are:

  • TSH (thyroid-stimulating hormone), which is made by your pituitary gland to control your thyroid gland
  • FT4 – free T4 (the active part of thyroxine)
  • FT3 – free T3 (the active part of triiodothyronine)

You may hear these blood tests referred to as ‘thyroid function tests’. If you have an overactive thyroid, you’ll have a low TSH level with a high FT4 level and a high FT3 level.

If the results of the blood tests show you have an overactive thyroid, your GP will refer you to see a specialist. This will be an endocrinologist, a doctor who specialises in treating hormone problems such as thyroid conditions.

Treatment of overactive thyroid

Treatment for overactive thyroid depends on what has caused it and how severe your symptoms are. Any treatment you have aims to lower your thyroid hormones levels, ease your symptoms and prevent complications.

There are three main treatments for an overactive thyroid:

  • medicines
  • radioactive iodine
  • surgery

Ask your doctor to explain which would be the best option for you in your particular circumstances.


When you’re first diagnosed as having an overactive thyroid, your doctor may recommend you take beta-blockers. These help to ease symptoms such as a fast heartbeat (palpitations) or shaking. You may need to take these until your thyroid hormone levels come down. If you can’t take a beta-blocker, you may be offered a medicine called a calcium channel blocker.

Your doctor may offer you antithyroid drugs, either carbimazole or propylthiouracil. These help to reduce the amount of hormone your thyroid gland produces. These medicines usually work quite quickly but it may be two to three weeks until you get the full benefit. You’ll be asked to take these medicines for 12 to 18 months. You may be able to stop taking them but for about one in two people, symptoms come back when they stop. If this happens, you may need to try a different treatment.

It’s very important to read the patient information that comes with your medicines carefully. This will give you information about possible side-effects and what you should do if you get them. If you have any queries about taking your medicine, you can ask your pharmacist.

Medicines for overactive thyroid and pregnancy

If you’re taking medicine for an overactive thyroid and you want to get pregnant, speak to your doctor. If at all possible, it’s best to plan your pregnancy and work with your doctor to manage your thyroid levels. Your doctor may recommend changing your medicine while you’re trying to get pregnant and during your first trimester (the first three months of your pregnancy). This is to make sure your baby has the fewest possible effects from your medicine.

Radioiodine treatment

Radioactive iodine aims to destroy tissue in your thyroid gland so that it produces fewer hormones. You take radioactive iodine as a drink. It takes around three to four months to work fully. Only the thyroid gland takes up the radioactive iodine, so it doesn’t harm other parts of your body.

You can’t have radioactive iodine treatment if you’re pregnant or breastfeeding. You should also use contraception for at least six months after your treatment. For more information about precautions you should take after radioactive iodine treatment, see our FAQ section.

After radioactive iodine treatment, most people won’t be able to make enough of the thyroid hormone their body needs to stay healthy. This is called hypothyroidism. So, if you’ve had radioactive iodine treatment, you’ll probably need to take replacement thyroid hormone (levothyroxine) for the rest of your life.


Another option for treating an overactive thyroid is to have all or most of your thyroid gland removed. Your doctor may suggest surgery if:

  • medicines and radioactive iodine treatments haven’t worked or you can’t take them
  • you have a very large goitre (swollen thyroid gland) which is putting pressure on your neck
  • you’re pregnant and unwilling or unable to take medicines

After the operation, depending on how much of your thyroid gland was removed, your body may not produce enough thyroid hormones. This means you might need to take replacement thyroid hormone (levothyroxine) for the rest of your life.

Monitoring your thyroid levels

During and after treatment for an overactive thyroid, you may need to have regular blood tests and check-ups. This is to measure the amount of thyroid hormones in your body and to check that treatment has worked. How often you’ll need these will depend on what caused your condition and what treatment you had. Your doctor will explain what you need to do.

Need a GP appointment? Telephone or Video GP service

With our GP services, we aim to give you an appointment the same day, subject to availability.

To book or to make an enquiry, call us on 0343 253 8381

Causes of overactive thyroid

Lots of things can cause overactive thyroid. The most common cause is a condition called Graves’ disease, which is an autoimmune disease. This means that your body mistakenly attacks your thyroid gland and it responds by producing too much hormone. Other causes of an overactive thyroid include:

  • conditions which produce swellings (nodules) on your thyroid gland
  • thyroiditis, which is inflammation of your thyroid gland sometimes caused by a viral infection
  • taking some medicines – for example, amiodarone and lithium

Complications of overactive thyroid

Most people with an overactive thyroid recover well after treatment. But some people may develop complications, some of which can be serious or life-threatening. The main complications are listed below.

  • Heart problems, such as heart failure or an irregular and fast heartbeat (atrial fibrillation).
  • Sight problems – if you have Graves’ disease, you may develop a condition called thyroid eye disease. You can find out more about this in our FAQ section.
  • Thyroid storm – this is a severe condition that needs emergency treatment. The symptoms include a fever, heart problems and restlessness.
  • If you’re pregnant, an uncontrolled overactive thyroid could affect your baby. They may be born early or underweight. An overactive thyroid can also lead to miscarriage. Tell your doctor if you’re planning a baby or think you might be pregnant.

After treatment for overactive thyroid

Treatment for overactive thyroid lowers the level of thyroid hormone in your body. It’s important to make sure that this doesn’t become too low because you could develop hypothyroidism. This is when you don’t have enough thyroid hormone in your body.

Your doctor will recommend that you have regular blood tests to check your thyroid hormone level. How often you need these will depend on your treatment and the results of previous tests. Ask your doctor to explain the plan for monitoring your thyroid hormone level.

The main symptoms of hypothyroidism are:

  • putting on weight
  • feeling the cold
  • dry skin and hair
  • lack of energy
  • constipation

If you’ve had treatment for overactive thyroid and you develop any of these symptoms, contact your GP.

The iodine used for this treatment is radioactive, but it’s generally very safe for you to have. After you’ve taken radioactive iodine, most of it leaves your body in your urine. Some also leaves your body in your sweat, tears, poo and saliva. This takes a few days to a week and as time goes on, the amount of radioactive iodine in your body gets less and less.

For a short time while your body is getting rid of the radioactive iodine, you’ll be asked to take precautions to keep others safe. These include being careful about what contact you have with other people, and for how long. Your doctor will give you clear advice about what you should do. Ask questions if you’re not sure about anything.

The advice will probably include:

  • limiting contact with babies, young children and pregnant women
  • staying away from crowded places where you’d be close to others for a long time (for example, in cinemas)
  • not sharing a bed
  • instructions about washing, laundry, and preparing food for others

You’ll be told how long you need to follow the precautions in your particular circumstances.

If you’re pregnant or breastfeeding, you shouldn’t have radioactive iodine. This is because radiation can pass through the placenta and into breast milk, so it may harm your baby. Ideally, wait six months after having your treatment before you try to get pregnant. Men should wait at least four months after treatment before trying for a baby.

If you have any concerns or questions about radioiodine treatment, talk to your doctor.

If you have an overactive thyroid caused by Graves’ disease, you could develop problems with your eyes. Around a quarter of all people with Graves’ disease develop a condition called Graves’ ophthalmopathy, also known as Graves' orbitopathy or thyroid eye disease. It’s more common in people who smoke.

The main symptoms of thyroid eye disease are:

  • bulging or staring eyes
  • swollen and red eyelids
  • watery eyes
  • an aching feeling behind your eye, which gets worse in the morning and when you move your eyes
  • red and irritated eyes
  • sensitivity to light
  • double vision, especially when you look upwards and to the side

Most people who have thyroid eye disease have mild eye problems, which may get better on their own or may need treatment. But it’s possible to develop more serious problems including ulceration of your cornea (the outer layer at the front of your eye) or even loss of sight.

So, if you have any of these symptoms it’s important to see your GP as soon as you can. Your GP may refer you to an ophthalmologist (a doctor who specialises in eye health, including eye surgery).

The type of treatment you have for thyroid eye disease depends on your symptoms and how severe they are. Treatments include eye drops, medicines (such as corticosteroids) and surgery.

If you have an overactive thyroid, it can affect your periods and your ability to get pregnant. Your periods may be shorter and happen more or less often. Or you may have no periods at all. Some thyroid conditions – for example, Graves’ disease – are also linked to conditions like endometriosis and polycystic ovary syndrome. These conditions can make getting pregnant even more difficult.

If you have problems getting pregnant, your doctor may do a blood test to measure your level of thyroid hormone. Treating any thyroid condition may help improve your chances of getting pregnant and having a healthy pregnancy.

You don’t need to follow any special diet if you have an overactive thyroid, just aim to eat healthily. After you’ve had treatment, you might want to consider what and how much you eat. For tips and advice about healthy eating and portion sizes, see our section: Related information. While your thyroid was producing too much hormone, you may have felt hungry and eaten more to keep your weight up. After your treatment, you may need to eat less to avoid putting on weight.

More on this topic

Did our Overactive thyroid (hyperthyroidism) information help you?

We’d love to hear what you think. Our short survey takes just a few minutes to complete and helps us to keep improving our health information.

This information was published by Bupa's Health Content Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals and deemed accurate on the date of review. Photos are only for illustrative purposes and do not reflect every presentation of a condition.

Any information about a treatment or procedure is generic, and does not necessarily describe that treatment or procedure as delivered by Bupa or its associated providers.

The information contained on this page and in any third party websites referred to on this page is not intended nor implied to be a substitute for professional medical advice nor is it intended to be for medical diagnosis or treatment. Third party websites are not owned or controlled by Bupa and any individual may be able to access and post messages on them. Bupa is not responsible for the content or availability of these third party websites. We do not accept advertising on this page.

  • Graves’ disease. BMJ Best practice., last reviewed October 2020
  • Toxic multinodular goitre. BMJ Best practice., last reviewed October 2020
  • Hyperthyroidism and thyrotoxicosis. Medscape., updated October 2020
  • Hyperthyroidism. Patient., last edited February 2020
  • Hyperthyroidism in pregnancy. Patient., last edited March 2020
  • Hypothyroidism. Patient., last edited February 2020
  • Thyroid eye disease. Patient., last edited December 2015
  • Hyperthyroidism. MSD Manuals., last full review/revision September 2020
  • Hyperthyroidism. NICE Clinical Knowledge Summaries., last revised February 2020
  • Hyperthyroidism. NICE British National Formulary., accessed November 2020
  • Carbimazole. NICE British National Formulary., accessed December 2020
  • Thyroid. Oxford Handbook of Endocrinology and Diabetes. Oxford Medicine Online., published online March 2014
  • Metabolism. Encyclopaedia Britannica., last updated October 2020
  • Hair loss and thyroid disorders. British Thyroid Foundation., accessed November 2020
  • Hyperthyroidism. British Thyroid Foundation., accessed November 2020
  • Radioactive iodine (I-131) therapy., reviewed January 2018
  • After radioactive iodine treatment. Cancer Research UK., last reviewed July 2018
  • Jeffreys A, Vanderpump M, Yasmin E. Thyroid dysfunction and reproductive health. The Obstetrician & Gynaecologist, 2015; 17:39–45. doi: 10.1111/tog.12161
  • Endometriosis. Patient., last edited September 2020
  • Polycystic ovary syndrome. Patient., last edited June 2016
  • Personal communication, Mr Robert Hardy, Consultant Surgeon, December 2020
The Patient Information Forum tick

Our information has been awarded the PIF tick for trustworthy health information.

Content is loading