What is an overactive thyroid?

Do you have symptoms of an overactive thyroid, or have you just received a diagnosis and would like to know more? We explore the causes, symptoms, testing, and treatments.

In this article, we cover: 

• What is an overactive thyroid?
• What causes an overactive thyroid?
• Signs and symptoms
• How is hyperthyroidism diagnosed?
• How to treat an overactive thyroid
• Associated health complications 
• How to test for an overactive thyroid

What is an overactive thyroid?
 

An overactive thyroid is where the thyroid gland makes too many thyroid hormones, which can include thyroxine (T4) and triiodothyronine (T3). This condition is also commonly known as hyperthyroidism.

Thyroid hormones play a part in many bodily functions, from heat regulation to metabolism. So, an excess of these hormones can lead to wide-ranging symptoms including weight loss, heat sensitivity, and an irregular or rapid heartbeat.

Thyrotoxicosis and hyperthyroidism: are they the same?

Although the terms are sometimes used interchangeably, thyrotoxicosis and hyperthyroidism don’t mean exactly the same thing.

Thyrotoxicosis is a term used to describe the clinical state of having too many circulating thyroid hormones. Hyperthyroidism, on the other hand, is an umbrella diagnosis. It covers a range of potential causes for having a thyroid gland that produces too many thyroid hormones. These include Grave’s disease, medication-induced hyperthyroidism, and thyroid gland inflammation (thyroiditis), but there are many more.

What causes an overactive thyroid?
 

There are several reasons why your thyroid might become overactive.

Causes of hyperthyroidism include: 

• Graves’ disease — an autoimmune thyroid condition where the immune system makes antibodies that cause the thyroid to overproduce thyroid hormones. This is the most common cause of hyperthyroidism (about four in five people with an overactive thyroid have Graves’ disease) [1].
• Thyroiditis — inflammation of the thyroid gland, which can cause excess thyroid hormone production. 
• Thyroid lumps (nodules) — lumps containing thyroid tissue that can make extra thyroid hormones. 
• Excess iodine — too much iodine can cause temporary hyperthyroidism. Foods, such as fish and dairy, contain iodine, and it’s also present in some medications like amiodarone, which is used to treat an irregular heartbeat.
• High levels of human chorionic gonadotrophin — this can happen in early pregnancy, a multiple pregnancy, or molar pregnancy (a lump of abnormal cells that grows in the womb instead of a foetus).
• Pituitary adenoma — a non-cancerous (benign) pituitary gland tumour.
• Thyroid cancer — rarely, a cancerous thyroid tumour can cause excess production of thyroid hormones.

Is an overactive thyroid hereditary?

A family history of hyperthyroidism can put you at increased risk of developing the condition. Graves’ disease has a strong genetic component and tends to run in families [2].

However, environmental and lifestyle factors also play a part. For example, studies show that smoking can increase the risk of Graves’ disease, and the condition occurs twice as frequently in smokers compared to non-smokers.

Other risk factors for hyperthyroidism include:

• Sex — an overactive thyroid can affect anyone, but it’s about ten times more common in women than men and typically happens between 20 and 40 years old [1].
• Age — the risk of developing an overactive thyroid increases with age, especially if you’re over 60.
• Pregnancy ­— a pregnancy can trigger hyperthyroidism, with risks to mother and baby if it isn’t well managed.
• Having another health condition — e.g. type 1 diabetes, adrenal insufficiency, or pernicious anaemia.

Signs and symptoms
 

Early signs of a thyroid condition can develop gradually or suddenly. For some people, symptoms are mild, while for others, they can be severe, significantly impacting their life. 

Common symptoms of an overactive thyroid include: 

• Anxiety and irritability 
• A rapid or irregular heartbeat
• A swelling in your neck from an enlarged thyroid gland (goitre) 
• Feeling tired all the time but finding it difficult to sleep
• Heat sensitivity and sweating 
• Nausea and frequent bowel movements 
• Weight loss, often with increased appetite 

These symptoms can have several causes. If you have symptoms, we recommend you see your doctor. A blood test can help determine whether your symptoms are caused by a thyroid condition.

How is hyperthyroidism diagnosed?
 

A hyperthyroidism diagnosis is typically based on symptoms and blood test results that show whether your thyroid is working properly.

A blood test to measure thyroid hormones is an accurate method of diagnosing hyperthyroidism. If your thyroid is overactive, your results typically show:

• Low levels of thyroid-stimulating hormone (TSH) and
• High levels of T4 and/or T3

If you’re diagnosed with hyperthyroidism, your doctor may refer you for further tests to identify the cause. A blood test to measure TSH receptor antibodies helps indicate if Graves’ disease is the likely cause of an overactive thyroid [3]. Your doctor may also request an ultrasound scan to check for problems such as lumps on the thyroid. 

How to treat an overactive thyroid
 

Although an overactive thyroid is usually a lifelong condition, it is treatable. Treatment will depend on the cause and severity of the condition. 

The three main treatments for hyperthyroidism: 

• Medication — anti-thyroid medications stop the thyroid from making excess hormones. The most common anti-thyroid drugs are called thionamides. You usually need to take this medication for several months before you notice any benefit. You may also be prescribed beta-blockers, which can help relieve some of your symptoms in the meantime.
• Radioactive iodine (or radioiodine) — a type of radiotherapy that destroys the cells in the thyroid that make thyroid hormones. It’s usually taken as an oral tablet or liquid, and is very effective, safe, and has minimal side effects. 
• Surgery — a thyroidectomy involves the removal of all or part of the thyroid. It may be recommended in certain situations, including where symptoms don’t respond to other treatment methods. If the thyroid gland is fully removed, you’ll need to take a thyroid hormone replacement, such as levothyroxine, for the rest of your life. 

Each treatment has its pros and cons. You’ll usually see a specialist in hormone-related health conditions (an endocrinologist) to discuss which treatment is best for you.

Can I manage hyperthyroidism naturally?

Although hyperthyroidism cannot be effectively managed without treatment, diet and lifestyle changes can complement treatment and help manage symptoms. 

Ways to support overactive thyroid treatment:

• Follow a thyroid-friendly diet — a low-iodine diet can help keep thyroid hormone levels in check. Healthy levels of vitamins and minerals including iron, selenium, vitamin D, and calcium are also essential for thyroid function.
• Take regular exercise — staying active can help manage your symptoms and reduce your risk of complications such as osteoporosis.
• Stop smoking — smoking not only increases the risk of Graves’ disease, but in people living with the condition, it’s linked to faster disease progression, a greater risk of developing eye problems, and a poorer response to treatment.
• Find ways to relax – stress can interfere with hormone balance, including thyroid function, so it’s important to find ways to relax and make sure you get good-quality sleep.

Can an overactive thyroid be cured? 

Hyperthyroidism is usually a lifelong condition, but there are situations where thyroid conditions can self-resolve. These include post-partum thyroiditis, which happens when the thyroid becomes inflamed after having a baby.

Although most cases of hyperthyroidism will not get better by themselves, effective treatments are available that can restore healthy thyroid function.

Associated health complications
 

An overactive thyroid can cause complications if it’s not treated appropriately or early enough.

Complications of hyperthyroidism include: 

• Eye problems — about a quarter of people with Graves’ disease develop thyroid eye disease (TED), also known as Graves’ ophthalmopathy. Symptoms include irritation, double vision, and bulging eyes.
• An underactive thyroid — radioactive iodine treatment for an overactive thyroid can make thyroid hormone levels too low. This is an underactive thyroid (or hypothyroidism). This is treatable with a daily thyroid hormone replacement.
• Pregnancy complications — these can happen when people have an existing thyroid condition or develop an overactive thyroid during pregnancy. High thyroid hormone levels can increase the risk of pre-eclampsia, premature birth, and miscarriage. Regular thyroid hormone checks during pregnancy can help detect any potential issues.
• Weakened bones (osteoporosis) — high levels of thyroid hormone can weaken your bones, making them more likely to break. Taking vitamin D and calcium supplements during treatment can help strengthen your bones. 
• Heart problems — an overactive thyroid can make it harder for your heart to pump blood around your body and increase your risk of atrial fibrillation — a heart condition that causes an irregular or abnormally fast heart rate.
• Thyroid storm — a rare health condition that usually occurs with undiagnosed or poorly controlled hyperthyroidism. A thyroid storm is a sudden and potentially life-threatening flare-up of symptoms, including a rapid heart rate, high blood pressure, and fever. 

How to test for an overactive thyroid
 

If you want to check your thyroid function, a blood test is a great first step. Our range of Thyroid Blood Tests can help you investigate your symptoms and monitor thyroid hormone levels with regular testing.

Not sure which test is right for you? Read our Thyroid Blood Test Buying Guide. You can also find more information in our Thyroid Hub.

The good news is that hyperthyroidism is very treatable, and you can live a healthy life with an overactive thyroid. Early diagnosis and management can improve symptoms and prevent future health complications.

References 

1. NHS (2023) Overactive thyroid (hyperthyroidism). Available at: <https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/> (Accessed: 26 March 2024). 
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3271308/
3. British Thyroid Foundation (2022) Hyperthyroidism. Available at: <https://www.btf-thyroid.org/hyperthyroidism-leaflet> (Accessed: 25 March 2024). 
4. Healthline (2022) Hyperthyroidism: Causes, Symptoms, Treatment, Diagnosis & More. Available at: <https://www.healthline.com/health/hyperthyroidism> (Accessed: 25 March 2024).