Hyperthyroidism (overactive thyroid)

Written by Emily Whitton
Emily Whitton
Nutritionist Resource Content Team

Last updated 9th April 2024 | Next update due 9th April 2027

Hyperthyroidism, or an overactive thyroid, is where the thyroid gland produces too much of the thyroid hormones, thyroxine and triiodothyronine. It is a medical condition that needs to be treated. Nutrition can also play a role in managing weight fluctuations - a key symptom of the condition. 

Here, we explore what hyperthyroidism is and how it can be managed, including with the support of a nutrition professional. 

What is hyperthyroidism? 

Hyperthyroidism, also known as an overactive thyroid, is a medical condition in which the butterfly-shaped thyroid gland (located at the base of the neck) makes and releases excess amounts of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3).

What does the thyroid gland do? 

The thyroid gland and the hormones within it help to control the body’s metabolism and the rate at which energy is burned. It also plays a crucial role in stabilising heart rate and body temperature. 

Having too much thyroid hormone (or too little) can cause an imbalance in the body. An excess amount can result in a fast metabolism, leading to a number of symptoms such as unexplained weight loss, a rapid or irregular heartbeat, and anxiety. It's therefore crucial that hyperthyroidism is treated. Below are some of the symptoms to look out for. 

Symptoms of hyperthyroidism

In the event that the body does begin to produce too many thyroid hormones, individuals may suffer from a variety of side effects which may include one or more of the following:

  • tiredness
  • mood swings, irritability
  • sleep disturbance/poor sleep
  • shakes/tremors
  • nervousness
  • anxiety
  • hair loss or thinning
  • muscle weakness
  • problems with conception

They may also experience:

  • palpitations and or increased heart rate
  • goitre, otherwise known as swelling of the thyroid gland
  • excessive sweating and/or an intolerance to heat
  • unexplained weight loss despite an increase in appetite (please note, a small number of individuals with hyperthyroidism will actually gain weight)
  • diarrhoea, and or an increase in the frequency of bowel movements
  • eye concerns such as swollen or red irritated eyes, and or double vision
  • shortness of breath, particularly during exercise or strenuous activity
  • infrequent or light periods, or periods stopping completely

If you are experiencing any of the above symptoms, the best course of action is to visit your GP who will be able to assess your symptoms, diagnose your condition and provide advice on the most appropriate medical care.

Diagnosing hyperthyroidism

Diagnosis of the condition will usually begin with the GP performing a standard examination as well as asking a series of questions about your symptoms to see if they can immediately identify any physical signs and telling factors. Below are some common indicative factors of hyperthyroidism that your GP may be looking out for:

  • swollen neck (which is caused by swelling of the thyroid gland)
  • inconsistencies in the coordination of your pulse and the rhythm of your heart
  • shaking/tremors
  • red palms
  • loosening of the nails from the nail bed
  • warm and moist skin
  • facial twitches and twitching limbs
  • hair loss and thinning
  • itchy skin

If your GP does suspect you may have an overactive thyroid, they may refer you for a blood test which will check the levels of your thyroid hormones. The different levels of hormones within the blood may also help your doctor determine the actual cause of your hyperthyroidism.

The test, known as a thyroid function test, involves taking a sample of your blood to test for levels of thyroid-stimulating hormone (TSH) and the thyroid hormones thyroxine (T4) and triiodothyronine (T3).

If the levels of thyroxine and triiodothyronine in the blood are normal, the pituitary gland will halt its production of TSH, and when the level of thyroxine and triiodothyronine drops, the pituitary gland will up its production of TSH in a bid to increase their levels.

If you are suffering from an overactive thyroid, the thyroid function test will usually identify lower-than-normal levels of TSH in your blood. These depleted levels mean that the thyroid gland is overproducing thyroid hormones, thus speeding up the metabolism and causing various unwanted symptoms and side effects.

If your thyroid function test does confirm that you have an overactive thyroid, your GP should be able to let you know whether it is what is known as an overt overactive thyroid or a subclinical overactive thyroid. The former term is used to describe the condition when it has reached its fully developed stage and will usually involve low levels of TSH and high levels of thyroid hormones and the latter describes the condition before it has developed fully. Here, levels of TSH are low and levels of the thyroid hormones are normal. In some cases, a subclinical overactive thyroid progresses into an overt overactive thyroid.

As well as undertaking tests to diagnose hyperthyroidism, your GP may also decide to refer you to an endocrinologist to try and establish the cause of your hyperthyroidism. An endocrinologist is a hormone specialist, who will be able to perform further tests which may reveal the cause of your overactive thyroid. Further tests may involve the following:

Ultrasound scan

An ultrasound scan will enable the endocrinologist to gauge the size of a goitre (swollen thyroid gland). It will also allow them to see whether it is putting pressure on the surrounding tissues in the neck.

Radioisotope (radionuclide scan)

This test involves a very small and harmless dose of a radioactive substance, such as iodine, being injected into the bloodstream. The medical professional performing the test will then pass a scanner over the neck so that overactive areas of the thyroid can be identified.

Causes of hyperthyroidism


Amiodarone is a form of medication which is used to treat heartbeat irregularities. The drug works by correcting the rhythm of the heart and slowing a heart that is beating too fast. Individuals who have non-toxic nodules in their thyroid gland may find that taking amiodarone can induce hyperthyroidism as it contains iodine.

Follicular thyroid cancer

Though cases such as this are rare, some individuals who have thyroid cancer may go on to develop hyperthyroidism as a result of the cancer cells in the thyroid gland beginning to produce thyroxine or triiodothyronine.

Graves' disease

Graves' disease is considered to be the most common cause of hyperthyroidism. This is an autoimmune condition, which weakens the immune system by mistaking healthy substances in the body for dangerous and toxic substances before attacking them. Graves' disease can be genetic and occur at any age.

According to NHS information, the condition is more common among women, notably those who are aged between 20 and 40, and is also more likely to develop in individuals who smoke.

In a healthy and normal immune system, the body manufactures antibodies which protect it from bacteria and infection. In an autoimmune disorder such as Graves' disease, the antibodies begin attacking the healthy tissue instead. The reason for this is unknown but in the case of Graves' disease, it could result in what is known as Graves’ ophthalmopathy. This causes the eyes to bulge out of their sockets, often causing double vision and also commonly leading to the development of hyperthyroidism.

Iodine supplements

The food we eat will usually contain enough iodine to keep the thyroid gland producing thyroid hormones. However, individuals who take extra iodine using supplements can find that this results in overproduction of the thyroid hormones.

This form of hyperthyroidism is known as iodine-induced hyperthyroidism and in most cases will usually only occur if non-toxic nodules are present in the thyroid gland.

Thyroid nodules

Approximately 2% of men and 8% of women develop thyroid lumps or nodules at some point during their lives. In 95% of cases, these lumps are benign, but for a small number of individuals, they are malignant.

Even though for most individuals with thyroid lumps the risk of developing cancer will be minor, the nodules can still contain what is known as ‘abnormal thyroid tissue’, which hinders the regular production of thyroid hormones, subsequently resulting in an overactive thyroid.

If only a single thyroid nodule or lump develops in your thyroid gland, this is known as a toxic thyroid nodule. If two thyroid lumps or nodules develop, this is known as a toxic multinodular goitre which, after Graves' disease, is said to be the second most common cause of hyperthyroidism, accounting for approximately 5% of cases.

Thyroid nodules are more common among those with a history of thyroid cancer so it is worth making yourself aware of your family medical history.

The nodules themselves may cause slight discomfort though in most cases, individuals either spot them in the mirror or are alerted to them by friends or family before they become aware of persistent pain.


The primary aim of treatment for hyperthyroidism is to ensure that the level of thyroid hormones in the blood returns to within what is considered to be the normal boundaries. Treatment may also be aimed at alleviating any associated conditions which may have arisen as a result of an overactive thyroid, for example, goitre. 

If you have been diagnosed with a subclinical overactive thyroid then it may be that you don’t require any treatment at all, as this strain of the condition sometimes returns to normal within a few months. However, if a subclinical overactive thyroid does progress into an overt overactive thyroid then treatment will be required.

Overt overactive thyroid treatment

If you have been diagnosed with overt overactive thyroid, typically, your GP will refer you for specialist treatment. Your specialist will assess your personal case and circumstances before then determining which treatment method is most appropriate. The key treatments are outlined below:


Propranolol and atenolol are two different types of beat-blockers which could help to relieve some of the symptoms of hyperthyroidism such as tremors, shakes, a rapid heartbeat and over-activity.

Beta-blockers are sometimes prescribed to those who are still going through the diagnostic process, or to those who are yet to see the benefits of thioamides (see below). Beta-blockers should not be taken by individuals who suffer from asthma and they could cause nausea, fatigue and sleep difficulties.

Thioamides (carbimazole and propylthiouracil)

This form of medication prevents the thyroid gland from producing excess amounts of thyroid hormones. Because the medication involves the production of the hormones as opposed to impacting their current levels, often individuals find it takes a few weeks before they begin to experience an improvement.

A specialist will monitor a patient’s development whilst they are taking the medication and when they begin to notice an improvement they may reduce the dosage slightly.

In a small number of cases these drugs do cause side effects such as joint pain and nausea, and in extremely rare cases can result in agranulocytosis - a serious blood condition which triggers a sudden and significant fall in the number of white blood cells. Most cases of agranulocytosis develop within three months of beginning a course of thioamides.

Radioiodine treatment

This treatment is a branch of radiotherapy which is commonly used for the treatment of many overactive thyroid cases. The treatment involves radioactive iodine which develops in the thyroid gland and shrinks it, reducing the volume of thyroid hormone that it can produce.

The treatment itself involves either swallowing a capsule or drinking a drink which contains a very low dosage of radioactive iodine. The quantity is so small that it is harmless, though pregnant women and women who are breastfeeding should note that this treatment is not suitable for them. Men should also note that it is inadvisable to father a child for at least four months after undergoing the treatment.

The aim of this treatment is to cause a build-up of radioactive iodine in the thyroid gland so that some of the tissue is destroyed, subsequently resulting in a reduction in the amount of thyroxine which is made.

Post-treatment, your specialist may advise you against engaging in prolonged contact with friends, family, colleagues, pets and the general public. Though the dosage of radioactive iodine is so low that it is not dangerous, this will ensure that exposure of radioactivity to others is kept to an absolute minimum. Contact with babies, children, pregnant women and pets is not recommended nor is visiting crowded public places such as the cinema or restaurants. These precautions only need to be applied for around two weeks after treatment and your specialist will be able to discuss this aspect of treatment with you in more detail. 

Surgery (thyroidectomy)

This form of treatment involves the removal of part of the thyroid gland. This method is one of the more invasive treatment options, but it does present a permanent solution to the problem of recurrent overactive thyroid.

Usually, this option is recommended to those who are affected by a severe goitre that is causing significant problems in the neck, as well as to individuals who have cancer of the thyroid, toxic multinodular goitre, or toxic thyroid nodule (adenoma).

Removing part of the thyroid gland will help to reduce the overproduction of thyroxine so that levels return to normal once again. Occasionally, too much of the thyroid is unknowingly taken and this could result in an underactive thyroid. Though this is a frustrating outcome, individuals to whom this happens can control their thyroid levels using medication.

Hyperthyroidism and nutrition

As mentioned, problems involving and affecting the thyroid also affect the body’s metabolism, its regulation, and the rate at which energy is burned.

Key symptoms of both hypothyroidism and hyperthyroidism involve sudden and unexplained fluctuations in weight. In some cases, unstable weight may be a result of an insufficient dosage of your current medication, which can be easily solved by paying a visit to your GP who will be able to tell you if this is the case. If not, it may be that some extra dietary advice is required from a professional such as a registered dietitian.

Nutritional professionals who can help with hyperthyroidism

Your GP may decide to refer you for a consultation with a nutritional professional or it may be that you have decided to do this independently. Either way, they will be able to work with you to formulate a personally tailored nutrition programme, which could help you to keep your weight stable, and under control.

Foods to avoid with hyperthyroidism 

The British Thyroid Foundation notes that there are no specific foods or supplements that can treat a thyroid disorder. Instead, eating a healthy, balanced diet is recommended to ensure you are getting a variety of foods in the right amounts. There are, however, some foods that are thought to affect thyroid function, so these should be kept to a minimum. These include: 

  • Seafood (including shellfish and seaweed or kelp) - seafood is high in iodine.
  • Gluten - in some cases, this can cause inflammation of the thyroid.
  • Caffeine - this can heighten some of the symptoms of hyperthyroidism such as nervousness, a rapid heart rate and anxiety.  

Generally, it is recommended to keep the consumption of iodine-rich foods to a minimum if you have hyperthyroidism. A low-iodine diet is one with less than 50 micrograms of iodine per day. 

Beneficial foods for an overactive thyroid 

The below foods are thought to support overall thyroid health for people with hyperthyroidism and may help manage symptoms. 

  • Low-iodine foods - including vegetables, egg whites and jams. 
  • Iron-rich foods (such as dark chocolate, lean meat, beans and spinach) - Iron supports thyroid function. Please note that some iron-rich foods may be high in iodine.
  • Selenium (e.g. Brazil nuts in small amounts) - supports thyroid health. 

Whilst there is no specific diet for hyperthyroidism, minimising and increasing certain foods may help to manage symptoms of an overactive thyroid. It is always recommended to consult a healthcare professional before making any changes to your diet or supplementing. 

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