Hyperthyroidism (Overactive Thyroid): Symptoms, Causes, and Treatment

Hyperthyroidism, or overactive thyroid, is when the thyroid gland in the neck makes more thyroid hormone than the body needs. Thyroid hormone sets the speed of the body, so an excess causes weight loss despite a normal or bigger appetite, a fast or irregular heartbeat, feeling hot and sweaty, shaky hands, anxiety, poor sleep and more frequent bowel movements. In the United States, the United Kingdom and Australia the most common cause is an autoimmune condition called Graves' disease, which causes about 8 in 10 cases. It is far more common in women. Diagnosis is a blood test showing a low (suppressed) TSH with a high free T4 or T3. Treatment options are anti-thyroid medicine (carbimazole or methimazole, sometimes propylthiouracil), radioactive iodine, or surgery to remove the thyroid; a beta blocker is often added to control the heart rate and tremor while other treatment takes effect. Overt hyperthyroidism affects roughly 5 in 1,000 adults.

In plain words

Hyperthyroidism means your thyroid gland makes too much thyroid hormone. The thyroid is a small gland in the neck. This hormone sets how fast your body works. When it is too high, your body speeds up. You may lose weight without trying. Your heart may beat fast or pound. You may feel hot, sweaty, shaky, or on edge. You may sleep badly and go to the toilet more often. The main cause is Graves' disease. In Graves' disease the immune system makes the thyroid work too hard. It is much more common in women. A blood test finds it. The test checks a hormone called TSH and the thyroid hormones. There are three main treatments: tablets that slow the thyroid down, a drink of radioactive iodine, or surgery to remove the thyroid. A beta blocker tablet is often added to slow a fast heart while the main treatment starts to work. Most people do well with treatment.

What is Hyperthyroidism (Overactive Thyroid): Symptoms, Causes, and Treatment?

Symptoms

Early symptoms

Weight loss with a normal or bigger appetite: Losing weight without trying, even while eating the same amount or more, because the body burns energy faster. (1) (3) (8)
Fast, pounding or irregular heartbeat: A resting pulse often above 100 beats per minute, a feeling of the heart racing or skipping, or palpitations. Some people develop an irregular rhythm called atrial fibrillation. (3) (8) (2)
Feeling hot and sweating easily: Being uncomfortably warm when others are not, sweating more than usual, and warm, moist skin. (1) (3) (7)
Shaky hands and feeling on edge: A fine tremor of the hands, restlessness, anxiety, irritability and mood swings. (1) (3) (8)
Trouble sleeping and tiredness: Difficulty falling or staying asleep, along with tiredness and muscle weakness, especially in the thighs and upper arms. (1) (3) (8)
More frequent or looser bowel movements: The gut speeds up, so bowel movements become more frequent and sometimes loose. (3) (2)
Neck swelling (goitre): The thyroid may enlarge and show as a swelling at the front of the lower neck. (1) (7)
Lighter or less frequent periods, and reduced fertility: In women, periods may become lighter, shorter or less frequent, and it can be harder to conceive. (3) (8)
Eye changes (in Graves' disease): Gritty, dry or bulging eyes, double vision or swollen eyelids can occur when Graves' disease affects the tissues around the eyes. This is called thyroid eye disease. (3) (7) (8)

Serious or emergency symptoms

A sudden, severe flare (thyroid storm): Thyroid storm is a rare, life-threatening surge of an overactive thyroid. Signs are a high fever, a very fast or irregular heartbeat, agitation, confusion or reduced consciousness, vomiting or diarrhoea, and sometimes yellowing of the skin. It is usually set off by an infection, surgery, injury, childbirth, or stopping anti-thyroid medicine, most often in someone whose overactive thyroid was untreated or poorly controlled. Call the emergency services now: 911 in the United States, 999 in the United Kingdom, or 000 in Australia. Thyroid storm needs intensive hospital treatment and is fatal in a significant share of cases, with a higher risk in older people. (3) (8) (1)
A new fast, irregular heartbeat with chest pain or breathlessness: An overactive thyroid can trigger atrial fibrillation or strain the heart, causing a fluttering irregular pulse, chest pain, dizziness or shortness of breath. Seek same-day medical care, or call the emergency services if the chest pain is severe or you feel faint. (8) (2)
Sudden severe sore throat, mouth ulcers or fever on anti-thyroid medicine: Carbimazole, methimazole and propylthiouracil can rarely cause a sharp drop in infection-fighting white blood cells, called agranulocytosis. A severe sore throat, mouth ulcers or a high fever can be the first sign. Do not take the next dose, contact a doctor or an urgent-care service the same day, and ask for an urgent blood count. Do not wait for a routine appointment. (3) (1) (8)

Causes

Primary causes

Graves' disease: An autoimmune condition in which antibodies switch the whole thyroid on, so it makes too much hormone. It is the most common cause in the United States, the United Kingdom and Australia, at roughly 8 in 10 cases, is far more common in women, often runs in families, and is the cause that can also affect the eyes. (1) (3) (8) (2)
Overactive thyroid nodules: One overactive lump (a toxic adenoma) or several (a toxic multinodular goitre) can make hormone on their own, outside the body's normal control. This is a more common cause in older people and in areas with low dietary iodine. (3) (8) (7)
Thyroiditis (thyroid inflammation): Inflammation of the thyroid, for example after a viral illness or after childbirth, can make stored hormone leak into the blood. This usually causes a temporary overactive phase that settles on its own, sometimes followed by a spell of underactivity. (3) (7) (8)

Contributing factors

Too much iodine: A large iodine load, for example from kelp or seaweed supplements, some cough medicines, or an iodine-based X-ray contrast dye, can push a susceptible thyroid into overactivity. (8) (7)
Medicines, especially amiodarone: The heart-rhythm drug amiodarone is iodine-rich and causes an overactive thyroid in roughly 1 in 10 people who take it. Lithium and some cancer immunotherapy drugs can also disturb the thyroid. (8) (1)
Taking too much thyroid hormone: Taking more levothyroxine than the body needs, whether by prescription error or deliberately, produces the same picture as an overactive thyroid. (3) (8)
Overactive thyroid in pregnancy: A pregnancy hormone (hCG) can mildly stimulate the thyroid in early pregnancy, and Graves' disease can first appear or flare around pregnancy. This needs specialist care. (8) (3)

Risk factors

Being a woman

Hyperthyroidism, and Graves' disease in particular, is several times more common in women than in men. (8) (7)

Family history of thyroid or autoimmune disease

Having a close relative with Graves' disease, another thyroid problem or another autoimmune condition raises your risk. (1) (7)

Smoking

Smoking makes Graves' disease and, especially, thyroid eye disease more likely and more severe. (7) (8)

Another autoimmune condition

Type 1 diabetes, coeliac disease, vitiligo and pernicious anaemia are linked with a higher chance of Graves' disease. (8) (2)

Recent pregnancy

The year after giving birth carries a higher risk of thyroiditis and of Graves' disease appearing or flaring. (8) (7)

A high iodine intake or amiodarone treatment

Large amounts of iodine, or the heart drug amiodarone, can trigger an overactive thyroid in people whose thyroid is prone to it. (8) (1)

Diagnosis

Hyperthyroidism is confirmed with a blood test. The first test is thyroid-stimulating hormone (TSH). When the thyroid is overactive the pituitary gland switches TSH off, so a low or undetectable TSH is the key finding. The laboratory then measures free thyroxine (free T4) and often triiodothyronine (T3). A low TSH with a high free T4 or T3 confirms overt hyperthyroidism. A low TSH with normal free T4 and T3 is called subclinical hyperthyroidism. To find the cause, doctors use a TSH-receptor antibody blood test (TRAb or TSI), which is positive in Graves' disease, and, if that is unclear, a radioactive-iodine uptake scan or a thyroid ultrasound with blood-flow imaging. This approach is the same in United States guidance from the American Thyroid Association, United Kingdom guidance from the NHS and NICE, and Australian guidance from the RACGP.

TSH, free T4 and T3

A low TSH with a high free T4 or T3 confirms an overactive thyroid and shows how severe it is. (3) (8) (1)

TSH-receptor antibodies (TRAb or TSI)

A positive result confirms Graves' disease, the most common cause, and often removes the need for a scan. (3) (8)

Radioactive-iodine uptake scan

Shows whether the whole gland is overactive (Graves'), one or more nodules are overactive, or the gland is barely taking up iodine (thyroiditis or too much iodine). (3) (8) (2)

Thyroid ultrasound

Shows the size of the gland, any nodules, and, with blood-flow imaging, helps tell Graves' disease from thyroiditis. (7) (8)

Treatment

Medication options

Anti-thyroid medicine

Carbimazole and methimazole (methimazole is carbimazole's active form) block the thyroid from making new hormone. One of them is usually the first treatment, especially for Graves' disease. Propylthiouracil is a third option, kept for the first three months of pregnancy, for thyroid storm, and for people who cannot take the others, because it has a higher risk of serious liver injury. Hormone levels usually improve over 4 to 8 weeks, and a course often lasts 12 to 18 months for Graves' disease, after which about half of people stay well. (1) (3) (8) (7)

Beta blocker

A beta blocker such as propranolol, atenolol or metoprolol quickly eases a fast heartbeat, palpitations, tremor and anxiety while the main treatment takes effect. It does not lower thyroid hormone levels or treat the cause. (3) (1) (2)

Radioactive iodine

A single drink or capsule of radioactive iodine is taken up by the overactive thyroid cells and gradually destroys them over weeks to months. It cures the overactive thyroid in about 8 in 10 people with Graves' disease and is a common definitive treatment. (3) (1) (8)

Surgery (thyroidectomy)

An operation to remove most or all of the thyroid quickly and reliably cures an overactive thyroid. It is chosen for a large goitre, when there are pressure symptoms, when there is significant thyroid eye disease, when other treatments cannot be used, or by preference. (3) (1) (7)

Lifestyle and self-care

Take medicine exactly as prescribed and keep blood tests: The dose of anti-thyroid medicine is guided by regular thyroid blood tests. Missing doses or tests can let the overactive thyroid rebound. (1) (3)
Know the warning signs to act on: Learn the signs of agranulocytosis (severe sore throat, mouth ulcers, fever) and of liver problems (yellow skin or eyes, dark urine). If they happen, hold the next dose and get urgent same-day medical care with a blood test. (3) (1)
Stop smoking: Smoking makes Graves' disease and thyroid eye disease worse. In Australia the Quitline (13 7848) can help; similar services exist in the US and UK. (7) (8)
Look after your eyes if you have thyroid eye disease: Use lubricating eye drops, wear sunglasses outdoors, and sleep with the head raised. Report new double vision, eye pain or reduced vision to an eye specialist urgently. (3) (1)
Avoid extra iodine and tell clinicians about your thyroid: Do not take kelp, seaweed or high-dose iodine supplements. Tell any doctor arranging a scan with contrast dye, or considering amiodarone, that you have thyroid disease. (8) (7)
Plan pregnancy with your specialist: If you might become pregnant, discuss which treatment is safest first. Anti-thyroid medicine choice changes in pregnancy and thyroid levels are checked often. (3) (8)

Always discuss dosing and treatment changes with your own prescriber.

Possible complications

Irregular heartbeat and heart failure: An untreated overactive thyroid raises the risk of atrial fibrillation, which itself raises the risk of stroke, and can weaken the heart muscle, causing heart failure. Both usually improve once the thyroid is controlled. (8) (2) (3)
Thinning bones (osteoporosis): Excess thyroid hormone speeds up bone loss, raising the risk of osteoporosis and fractures, particularly in women after the menopause. (7) (8) (2)
Thyroid eye disease (Graves' ophthalmopathy): In Graves' disease, swelling of the tissues around the eyes can cause bulging, grittiness, double vision and, rarely, threat to sight. Smoking makes it worse. It is managed by an eye specialist. (3) (7)
Pregnancy problems: Poorly controlled hyperthyroidism in pregnancy raises the risk of miscarriage, pre-eclampsia, premature birth, low birth weight and thyroid problems in the baby. With specialist care these risks are much lower. (8) (7) (3)
Thyroid storm: A rare, life-threatening surge with high fever, a very fast heartbeat and confusion. It needs emergency hospital treatment and carries a real risk of death, higher in older people. (3) (8)

When to see a doctor

Routine follow-up

Book an appointment if you have symptoms such as unexplained weight loss, a fast or pounding heartbeat, feeling hot and sweaty, shaky hands, anxiety or looser bowels for more than a week or two, so a thyroid blood test can be done. (1) (7)
See your doctor if you are being treated for an overactive thyroid and symptoms return or change, or if you develop new eye symptoms such as bulging, double vision or eye pain. (3) (7)
Contact your specialist promptly if you have an overactive thyroid and are pregnant or planning a pregnancy, because treatment needs to be reviewed. (3) (8)

Seek emergency care

Call the emergency services now, 911 in the United States, 999 in the United Kingdom or 000 in Australia, if a person with an overactive thyroid has a high fever with a very fast or irregular heartbeat and becomes agitated, confused or hard to rouse. This may be thyroid storm, a medical emergency. (3) (8) (1)
Seek urgent same-day care and ask for a blood count if you are taking carbimazole, methimazole or propylthiouracil and develop a severe sore throat, mouth ulcers or a high fever, as this can be a sign of a dangerously low white blood cell count. (3) (1) (8)

Frequently asked questions

What is the difference between hyperthyroidism and hypothyroidism?

Hyperthyroidism means the thyroid makes too much hormone, which speeds the body up and causes weight loss, a fast heartbeat and feeling hot. Hypothyroidism is the opposite: too little hormone slows the body down, causing tiredness, weight gain and feeling cold. A blood test tells them apart. (1) (2) (3)

What are the first signs of an overactive thyroid?

Common early signs are losing weight without trying, a fast or pounding heartbeat, feeling hot and sweating easily, shaky hands, feeling anxious or irritable, poor sleep and more frequent bowel movements. There may also be a swelling in the neck. (1) (3) (8)

Is hyperthyroidism the same as Graves' disease?

No. Graves' disease is an autoimmune condition and the most common single cause of an overactive thyroid, about 8 in 10 cases. Other causes are overactive thyroid nodules, thyroid inflammation, too much iodine and some medicines. Testing shows which one you have. (1) (3) (8)

How is hyperthyroidism diagnosed?

With a blood test. A low or undetectable TSH is the key sign, and the diagnosis is confirmed by a high free T4 or T3. A TSH-receptor antibody test (TRAb or TSI) confirms Graves' disease, and a radioactive-iodine uptake scan or ultrasound is used if the cause is unclear. (3) (8) (1)

What are the treatment options?

There are three main treatments: anti-thyroid medicine (carbimazole or methimazole, sometimes propylthiouracil), radioactive iodine, and surgery to remove the thyroid. A beta blocker is often added early to settle the heart rate and tremor. The best choice depends on the cause, its severity, your age, whether you have eye disease, and whether you are or may become pregnant. (3) (1) (7)

How long does treatment take to work?

A beta blocker eases symptoms within hours to days. Anti-thyroid medicine usually brings hormone levels down over 4 to 8 weeks, and a course for Graves' disease often lasts 12 to 18 months. Radioactive iodine and surgery work over weeks but often lead to an underactive thyroid that then needs a daily levothyroxine tablet for life. (3) (1) (8)

Can hyperthyroidism go away on its own?

Some causes are temporary, such as thyroid inflammation after a viral illness or after childbirth, and can settle without specific treatment. Graves' disease and overactive nodules usually do not go away on their own and need treatment. (3) (7) (8)

What is a thyroid storm?

Thyroid storm is a rare, life-threatening surge of an overactive thyroid, with a high fever, a very fast or irregular heartbeat and confusion. It is usually triggered by an infection, surgery, injury or stopping anti-thyroid medicine, and needs emergency hospital care. Call 911, 999 or 000. (3) (8) (1)

Which anti-thyroid medicine warning signs should I act on?

Get urgent same-day medical care, and hold the next dose until a doctor has reviewed you, if you get a severe sore throat, mouth ulcers or a high fever (possible low white blood cell count), or yellow skin or eyes, dark urine or severe tummy pain (possible liver injury). Ask for an urgent blood test. Do not wait for a routine appointment. (3) (1) (8)

Can I get pregnant if I have hyperthyroidism?

Yes, but it should be planned with a specialist. Uncontrolled hyperthyroidism raises risks for mother and baby. The choice of anti-thyroid medicine changes in pregnancy: propylthiouracil is generally used in the first three months and carbimazole or methimazole after that. Thyroid levels are checked often. (3) (8) (2)

Will I need to take levothyroxine after treatment?

Often, yes. Radioactive iodine and surgery, and sometimes anti-thyroid medicine, can leave the thyroid underactive. If that happens you take a daily levothyroxine tablet, with blood tests to set the dose, as for hypothyroidism. (3) (1)

References

NHS — Overactive thyroid (hyperthyroidism) source 1
MedlinePlus (US National Library of Medicine) — Hyperthyroidism source 2
American Thyroid Association — Hyperthyroidism (patient information) source 3
Mayo Clinic — Hyperthyroidism: Symptoms & causes source 4
Mayo Clinic — Hyperthyroidism: Diagnosis & treatment source 5
Cleveland Clinic — Hyperthyroidism source 6
healthdirect (Australia) — Hyperthyroidism source 7
StatPearls / NCBI Bookshelf — Hyperthyroidism source 8