Thyroid Disorders: The Complete Guide to Underactive and Overactive Thyroid

Thyroid disorders are among the most common hormone conditions in the world. Hundreds of millions of people live with an underactive or overactive thyroid, thyroid nodules or goitre, and many more do not know they have a problem. Women are several times more likely than men to be affected. Because thyroid hormones influence almost every organ, symptoms are often vague and easily blamed on stress, ageing, menopause or depression.

The good news is that most thyroid conditions are easy to diagnose with a blood test and can be treated effectively. This complete guide explains what the thyroid does, the symptoms of underactive and overactive thyroid, the main causes including Hashimoto’s thyroiditis and Graves’ disease, how to read thyroid blood tests, how to take thyroid medicines properly, what goitre and nodules mean, the role of iodine, thyroid health in pregnancy, and the warning signs that need urgent care.

What does the thyroid do?

The thyroid is a small, butterfly-shaped gland at the front of the neck, just below the Adam’s apple. It produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T4 is the main hormone released, and it is converted in body tissues into T3, the more active form.

Thyroid hormones act like the body’s accelerator. They control the speed of metabolism: how quickly the body uses energy, and how fast the heart beats, the gut moves, the brain processes information and the body produces heat. They are also essential for normal growth and brain development in babies and children.

The thyroid is controlled by the pituitary gland in the brain, which releases thyroid-stimulating hormone (TSH). When thyroid hormone levels fall, the pituitary releases more TSH to stimulate the thyroid. When levels rise, TSH falls. This feedback loop is why TSH is the most useful first test of thyroid function.

The thyroid needs iodine, obtained from the diet, to make its hormones.

Hypothyroidism: underactive thyroid

Hypothyroidism occurs when the thyroid does not produce enough hormone, so body processes slow down. It is one of the most common hormone disorders, especially in women and older adults.

Symptoms

Symptoms usually develop slowly over months or years, and many people have only a few:

• Tiredness and sluggishness.
• Feeling cold.
• Weight gain, usually modest.
• Constipation.
• Dry skin and brittle nails.
• Thinning or coarse hair, and loss of the outer part of the eyebrows.
• Low mood or depression.
• Poor memory and concentration (“brain fog”).
• Muscle aches, cramps and weakness.
• Joint pain and stiffness.
• Heavy or irregular periods, and fertility problems.
• Slow heart rate.
• Puffy face and eyes.
• Hoarse voice.
• Carpal tunnel syndrome (tingling in the hands).
• Raised cholesterol.
• A swelling in the neck (goitre) in some people.

In older adults, symptoms may be subtle and mistaken for ageing or dementia.

Causes

• Hashimoto’s thyroiditis (autoimmune thyroiditis): the most common cause in countries with adequate iodine. The immune system attacks the thyroid, gradually reducing its ability to make hormone. It runs in families and is more common in women and in people with other autoimmune conditions such as type 1 diabetes, coeliac disease, vitiligo and pernicious anaemia.
• Iodine deficiency: still the leading cause of hypothyroidism and goitre worldwide, particularly in regions where soils are low in iodine and salt is not iodised.
• Treatment for hyperthyroidism: radioactive iodine or surgery often leaves the thyroid underactive.
• Thyroid surgery for nodules, goitre or cancer.
• Radiotherapy to the neck.
• Medicines such as lithium, amiodarone, some cancer immunotherapies and interferon.
• Postpartum thyroiditis, which may be temporary.
• Congenital hypothyroidism: present from birth. Many countries screen all newborns with a heel-prick blood test, because early treatment prevents serious problems with growth and brain development.
• Pituitary problems (secondary hypothyroidism), which are rare.

Subclinical hypothyroidism

Subclinical hypothyroidism means TSH is raised but T4 is still within the normal range. It is common, especially in older adults. Many people have no symptoms, and some will return to normal on repeat testing. Treatment depends on the TSH level, symptoms, age, pregnancy plans and whether thyroid antibodies are present. Guidelines generally recommend treatment if TSH is persistently above around 10 milliunits per litre, in pregnancy or when planning pregnancy, and sometimes for younger people with symptoms at lower levels. Older adults with mildly raised TSH often do not benefit from treatment.

Hyperthyroidism: overactive thyroid

Hyperthyroidism occurs when the thyroid produces too much hormone, speeding up body processes. Thyrotoxicosis is the broader term for symptoms caused by excess thyroid hormone from any source.

Symptoms

• Nervousness, anxiety and irritability.
• Feeling hot and sweating excessively.
• Fast or irregular heartbeat (palpitations).
• Weight loss despite a normal or increased appetite.
• Tremor, especially of the hands.
• Difficulty sleeping.
• Tiredness and muscle weakness, especially in the thighs and upper arms.
• Frequent bowel movements or diarrhoea.
• Lighter or less frequent periods.
• Thinning hair.
• Shortness of breath.
• A swelling in the neck (goitre).
• Eye problems in Graves’ disease.

Older adults may have fewer typical symptoms and instead present with weight loss, low mood, atrial fibrillation (an irregular heart rhythm) or heart failure. This is sometimes called “apathetic hyperthyroidism”.

Causes

• Graves’ disease: the most common cause. It is an autoimmune condition in which antibodies stimulate the thyroid to produce too much hormone. It is more common in women aged 20 to 50 and in smokers, and runs in families.
• Toxic multinodular goitre: lumps in an enlarged thyroid produce excess hormone independently. More common in older adults and in regions with historical iodine deficiency.
• Toxic adenoma: a single overactive thyroid nodule.
• Thyroiditis: inflammation of the thyroid releases stored hormone, causing temporary hyperthyroidism, often followed by a period of hypothyroidism. Types include painful subacute thyroiditis after viral infections, painless thyroiditis and postpartum thyroiditis.
• Medicines: taking too much thyroid hormone, amiodarone, and iodine-containing contrast dyes or supplements in some people.

Graves’ disease and the eyes

Around a quarter to a half of people with Graves’ disease develop thyroid eye disease (Graves’ orbitopathy), although it is often mild. The same immune process causes inflammation and swelling of the muscles and tissues behind the eyes. Symptoms include:

• Gritty, dry or watery eyes.
• Redness and swelling of the eyelids.
• Bulging eyes.
• Sensitivity to light.
• Double vision.
• Pain behind the eyes.
• In rare severe cases, reduced vision or colour vision, which is an emergency.

Smoking greatly increases the risk and severity of thyroid eye disease, and stopping smoking is one of the most important steps. Lubricating eye drops, sunglasses and raising the head of the bed help mild symptoms. Selenium supplements may help mild disease in some regions. Moderate to severe disease needs specialist treatment, sometimes with steroids, other immune treatments or surgery. Seek urgent help for any loss of vision.

Thyroid blood tests explained

Thyroid function is assessed with simple blood tests:

• TSH: the main screening test. A high TSH usually means the thyroid is underactive; a low TSH usually means it is overactive.
• Free T4: measures the active, unbound thyroxine in the blood.
• Free T3: useful mainly in hyperthyroidism.
• Thyroid antibodies: thyroid peroxidase (TPO) antibodies suggest autoimmune thyroiditis (Hashimoto’s). TSH receptor antibodies (TRAb) confirm Graves’ disease.

Typical patterns are:

• High TSH, low free T4: overt hypothyroidism.
• High TSH, normal free T4: subclinical hypothyroidism.
• Low TSH, high free T4 or T3: overt hyperthyroidism.
• Low TSH, normal free T4 and T3: subclinical hyperthyroidism.

Normal ranges vary slightly between laboratories. Results can be affected by acute illness, some medicines, pregnancy, and biotin (vitamin B7) supplements, which can interfere with some laboratory tests. Stop biotin supplements for a few days before testing if advised. Other investigations may include a thyroid ultrasound scan and a thyroid uptake scan, which shows how actively the gland is taking up tracer.

Treating hypothyroidism

Levothyroxine

Hypothyroidism is treated by replacing the missing hormone with levothyroxine, a synthetic form of T4. It is one of the most commonly prescribed medicines in the world, is inexpensive and, when taken correctly, is very safe.

How to take levothyroxine for best results:

• Take it at the same time every day, usually in the morning on an empty stomach, with water, 30 to 60 minutes before breakfast. Some people take it at bedtime, at least three to four hours after the last meal; consistency matters most.
• Avoid taking it with coffee, milk, soya, high-fibre foods, calcium, iron, antacids, proton pump inhibitors and some other medicines, which reduce absorption. Leave at least four hours between levothyroxine and calcium or iron supplements.
• Stick with the same brand or formulation where possible, as switching can change your levels slightly.
• Do not stop without advice. Hypothyroidism is usually lifelong.

Finding the right dose

The starting dose depends on age, weight, heart health and severity. Younger healthy adults may start on a full dose; older adults and people with heart disease start low and increase slowly to avoid straining the heart. TSH is checked six to eight weeks after starting or changing the dose, and the dose adjusted until TSH is in the target range. Once stable, TSH is usually checked once a year. It can take several months to feel fully better.

Taking too much

Too much levothyroxine can cause symptoms of hyperthyroidism, and over the long term increases the risk of atrial fibrillation and osteoporosis, especially in older adults. Regular monitoring helps avoid this.

What if I still feel unwell on levothyroxine?

Most people feel much better once their TSH is in range, but a minority continue to have symptoms. Possible reasons include:

• The dose not being quite right, or absorption being affected by timing or other medicines.
• Another condition causing tiredness, such as anaemia, vitamin B12 or vitamin D deficiency, coeliac disease, diabetes, sleep apnoea, depression or menopause.
• Lifestyle factors such as poor sleep and stress.

Some people ask about T3 (liothyronine) or desiccated thyroid extract. Current evidence does not show that most people benefit from these, and they carry risks if not carefully monitored. Some guidelines allow a trial of combination therapy under specialist supervision for people with persistent symptoms despite optimal levothyroxine and after other causes have been excluded. Avoid buying thyroid products online without medical supervision.

Treating hyperthyroidism

Treatment depends on the cause, severity, age, pregnancy plans and personal preference. Options are often discussed together with an endocrinology specialist.

Beta blockers

Medicines such as propranolol quickly reduce symptoms like palpitations, tremor and anxiety while other treatments take effect. They do not treat the underlying cause.

Antithyroid medicines

Carbimazole, methimazole and propylthiouracil (PTU) reduce the production of thyroid hormone. They usually take several weeks to work.

• For Graves’ disease, a course of 12 to 18 months leads to long-term remission in around half of people. Some people choose longer-term low-dose treatment.
• A rare but serious side effect is agranulocytosis, a sharp fall in infection-fighting white blood cells. If you take antithyroid medicine and develop a sore throat, mouth ulcers, fever or other signs of infection, stop the medicine and get an urgent blood count.
• Other side effects include rash, itching and, rarely, liver problems, particularly with PTU.
• Carbimazole and methimazole can harm an unborn baby in early pregnancy, so PTU is usually preferred in the first trimester. Discuss pregnancy plans with your specialist.

Radioactive iodine

A single capsule or drink of radioactive iodine is taken up by the thyroid and gradually destroys overactive thyroid tissue over weeks to months. It is effective and widely used, particularly for Graves’ disease relapse and toxic nodules. Most people eventually become hypothyroid and need lifelong levothyroxine. It is not used in pregnancy or breastfeeding, and pregnancy should be avoided for at least six months afterwards. Temporary precautions to limit close contact with others, especially children and pregnant women, are needed for a short period. It may worsen active thyroid eye disease.

Surgery

Removing all or most of the thyroid (thyroidectomy) is an option for large goitres causing pressure symptoms, suspected cancer, severe eye disease, or when other treatments are unsuitable. Lifelong levothyroxine is then needed. Risks include damage to the nerves controlling the voice and to the parathyroid glands that regulate calcium.

Thyroiditis

Thyroiditis-related hyperthyroidism is usually temporary and treated with beta blockers and pain relief, with monitoring for a later underactive phase.

Goitre and thyroid nodules

Goitre

A goitre is an enlarged thyroid gland. It can occur with normal, low or high thyroid function. Worldwide, iodine deficiency is the most common cause. Other causes include Hashimoto’s thyroiditis, Graves’ disease and multinodular goitre. Many goitres cause no symptoms, but large ones can cause difficulty swallowing, breathing problems, a feeling of pressure, or hoarseness.

Thyroid nodules

Thyroid nodules are lumps in the thyroid. They are extremely common, found in up to half of older adults on ultrasound, and the vast majority are benign. A nodule found by touch or on a scan is usually assessed with:

• Thyroid function tests.
• A thyroid ultrasound, which helps assess the risk of cancer based on the nodule’s features.
• Fine-needle aspiration (a needle biopsy) for nodules with suspicious features or above a certain size.

See a healthcare provider promptly if you notice a new or growing neck lump, especially with hoarseness lasting more than a few weeks, difficulty swallowing or breathing, or swollen lymph nodes in the neck.

Thyroid cancer

Thyroid cancer is relatively uncommon and usually has an excellent outlook, especially the most common type, papillary thyroid cancer. It is typically treated with surgery, sometimes followed by radioactive iodine. Increased use of ultrasound has led to more small cancers being found, many of which would never have caused harm, so careful decisions about testing and treatment are important.

Iodine: getting the balance right

Iodine is essential for making thyroid hormones. Iodine deficiency remains a major global public health issue and is the world’s most preventable cause of brain damage, because deficiency in pregnancy and early childhood impairs brain development. Universal salt iodisation, supported by the World Health Organization and UNICEF, has dramatically reduced deficiency in many countries, but pockets remain, and some people, particularly pregnant women and those who avoid dairy, fish or iodised salt, may not get enough.

Good sources of iodine include iodised salt, seafood, seaweed, dairy products and eggs. Adults need around 150 micrograms a day, and pregnant and breastfeeding women around 250 micrograms a day. Many countries recommend iodine-containing supplements in pregnancy, especially where intake may be low.

Too much iodine can also cause thyroid problems in some people, for example from high-dose kelp or seaweed supplements, some cough medicines and contrast dyes. Avoid high-dose iodine supplements unless advised.

Thyroid health in pregnancy

Thyroid hormones are vital for a baby’s brain development, particularly in the first trimester, when the baby relies on the mother’s thyroid hormone.

• If you take levothyroxine and become pregnant, contact your healthcare provider as soon as you have a positive pregnancy test. Your dose usually needs to increase, often by around 25 to 30 percent, straight away. Many guidelines advise taking two extra doses a week until you are seen. TSH is checked every four to six weeks during the first half of pregnancy.
• If you have hyperthyroidism and are planning pregnancy, discuss your treatment with a specialist beforehand. Graves’ disease antibodies can cross the placenta and affect the baby’s thyroid, so monitoring is important.
• Postpartum thyroiditis affects some women in the year after giving birth. It may cause a brief overactive phase followed by an underactive phase. Symptoms such as tiredness and low mood can be mistaken for the normal demands of a new baby or postnatal depression. A blood test can help.

Women with thyroid conditions can have healthy pregnancies with good management.

Thyroid emergencies

Seek emergency care immediately for:

• Thyroid storm: a rare, life-threatening worsening of hyperthyroidism, often triggered by infection, surgery or stopping medicine. Signs include high fever, very fast heartbeat, agitation, confusion, vomiting, diarrhoea and collapse.
• Myxoedema coma: a rare, life-threatening complication of severe untreated hypothyroidism, usually in older adults, often triggered by infection or cold. Signs include extreme drowsiness, confusion, low body temperature and slow breathing.
• Agranulocytosis on antithyroid medicine: sore throat, fever or mouth ulcers.
• Sudden vision loss or severe eye pain with thyroid eye disease.
• Breathing difficulty from a large neck swelling.

Living well with a thyroid condition

• Take your medicines consistently, and keep a record of your doses and blood test results.
• Have regular blood tests as advised, and after any dose change.
• Tell any healthcare provider who treats you about your thyroid condition and medicines.
• Eat a balanced diet. There is no special “thyroid diet”, and most people do not need to avoid foods such as cabbage or broccoli in normal amounts.
• Be cautious with supplements marketed for “thyroid support”, which may contain thyroid hormone or excess iodine.
• Stop smoking, especially if you have Graves’ disease.
• Stay active and look after your mental health.

A note for nurses and healthcare workers

Thyroid problems are common among patients of every age, and nurses are often the first to notice patterns: tiredness and weight change, a new irregular pulse, low mood in a new mother, or confusion in an older person. Nurses can help by recognising possible thyroid symptoms and prompting testing, teaching correct levothyroxine timing, checking for interacting medicines, reminding patients to increase their dose when pregnant, and making sure patients on antithyroid medicines know to report sore throat and fever immediately. In newborn care, ensuring heel-prick screening is done and results are followed up prevents lifelong disability.

Common myths about thyroid disorders

• “My weight gain must be my thyroid.” Hypothyroidism usually causes only modest weight gain, largely fluid. Treating it helps, but it is rarely the only cause of significant weight gain.
• “Normal TSH means I can’t have a thyroid problem.” TSH is very reliable for most people, but pituitary conditions and some medicines can affect results.
• “Natural thyroid supplements are safer.” Unregulated products can contain variable amounts of hormone and cause harm.
• “I must avoid all cruciferous vegetables.” In normal dietary amounts, they do not cause thyroid problems for most people.
• “Once my thyroid is treated, I don’t need follow-up.” Regular checks keep your dose right over time.

Thyroid conditions in children and teenagers

Thyroid problems can occur at any age. In newborns, congenital hypothyroidism affects roughly one in 2,000 to 4,000 babies. Because babies often show no obvious signs at first, newborn screening programmes are vital. When the condition is found and treated within the first two weeks of life with daily levothyroxine, children usually grow and develop normally. Without treatment, it causes severe and permanent intellectual disability and poor growth. Parents of babies on levothyroxine are taught to crush the tablet and give it with a small amount of water or breast milk, and to attend regular blood tests, as the dose changes frequently as the child grows.

In older children and teenagers, Hashimoto’s thyroiditis is the most common cause of an underactive thyroid. Signs may include slowing of growth, delayed puberty, tiredness, poor school performance, weight gain and constipation. Graves’ disease can also occur in adolescents, causing weight loss, anxiety, poor concentration, rapid growth and sleep problems, which can be mistaken for behavioural issues. Treatment principles are similar to adults, but care is usually led by children’s specialists.

Thyroid conditions in older adults

Thyroid disorders become more common with age, but symptoms are often less obvious. An underactive thyroid in an older person may show up only as tiredness, constipation, feeling cold, low mood, memory problems or unsteadiness, all of which are easily attributed to ageing. An overactive thyroid may cause weight loss, weakness, low mood or atrial fibrillation rather than the classic nervousness and tremor. Treatment needs extra care: levothyroxine is started at low doses and increased slowly to protect the heart, and older adults are particularly vulnerable to the effects of too much thyroid hormone, including atrial fibrillation and bone loss. Many older people with mildly raised TSH do not need treatment at all, as TSH naturally rises a little with age.

The thyroid and the heart

Thyroid hormones have powerful effects on the heart. An overactive thyroid speeds the heart, increases the risk of atrial fibrillation (an irregular heartbeat that increases stroke risk) and can cause or worsen heart failure, particularly in older adults or people with existing heart disease. Anyone newly diagnosed with atrial fibrillation should have their thyroid function checked. An underactive thyroid slows the heart, raises cholesterol and can contribute to fluid around the heart and heart failure in severe cases. Treating the thyroid condition often improves these heart effects. Never stop or change thyroid medicines without advice if you have heart disease, as changes can affect your heart rhythm.

Diet, selenium and Hashimoto’s

Many people with Hashimoto’s thyroiditis look for diets that might slow the condition. The evidence is limited:

• Gluten-free diets are essential for people with coeliac disease, which is more common in people with autoimmune thyroid disease. Testing for coeliac disease is worthwhile if you have gut symptoms, anaemia or unexplained difficulty absorbing levothyroxine. For people without coeliac disease, there is not enough evidence to recommend a gluten-free diet for Hashimoto’s.
• Selenium is a mineral needed for thyroid hormone metabolism. Some studies suggest selenium supplements reduce thyroid antibody levels, but there is no clear evidence that they improve symptoms or prevent hypothyroidism. Too much selenium is toxic. Brazil nuts, fish, eggs and wholegrains provide selenium in the diet.
• Iodine should be adequate but not excessive. High-dose iodine or kelp supplements can worsen autoimmune thyroiditis in some people.
• Soya in normal dietary amounts does not cause hypothyroidism, but it can reduce levothyroxine absorption, so take your tablet well apart from soya products.

A balanced diet with adequate iodine, plenty of vegetables, fruit, wholegrains and protein supports overall health. Beware of expensive programmes and supplements promising to “heal” the thyroid.

Thyroid conditions and mental health

Thyroid hormones affect the brain, and both underactive and overactive thyroid can cause significant mental health symptoms. Hypothyroidism can cause depression, slowed thinking, poor memory and, rarely in severe cases, psychosis. Hyperthyroidism can cause anxiety, panic attacks, irritability, insomnia, restlessness and mood swings. These symptoms usually improve with treatment of the thyroid, but this can take weeks to months. If mood symptoms persist after thyroid levels are normal, they deserve their own assessment and treatment. Living with a long-term condition, body changes and eye disease can also affect wellbeing and self-image. Support from healthcare providers, patient organisations and peer groups can help.

Thyroid conditions and menopause

Thyroid problems are common in women around the age of menopause, and the symptoms overlap: tiredness, low mood, poor sleep, weight change, changes in periods, hot flushes or feeling cold, and brain fog. This overlap means thyroid problems can be missed, or menopause symptoms can be wrongly blamed on the thyroid. A TSH test helps tell the difference. Women taking levothyroxine who start oral hormone replacement therapy may need a dose adjustment, so TSH is often checked a few months after starting.

Medicines that affect thyroid function

Some commonly used medicines affect the thyroid or thyroid tests:

• Amiodarone, a heart rhythm medicine rich in iodine, can cause both underactive and overactive thyroid. Thyroid function is checked before and regularly during treatment.
• Lithium, used for bipolar disorder, commonly causes hypothyroidism and goitre. Regular thyroid tests are needed.
• Immune checkpoint inhibitors, a type of cancer immunotherapy, frequently cause thyroiditis.
• Oral oestrogen, including some contraceptive pills and HRT, increases thyroid-binding proteins and may increase levothyroxine needs.
• Calcium, iron, antacids, proton pump inhibitors and some cholesterol medicines reduce levothyroxine absorption.
• Biotin supplements can make some thyroid blood tests inaccurate.

Always tell your healthcare provider and pharmacist about all medicines and supplements you take.

Thyroid care around the world

Iodine deficiency remains the leading cause of thyroid disorders in many low- and middle-income regions, especially mountainous and inland areas far from the sea. Salt iodisation has transformed this picture in many countries, but monitoring and enforcement remain essential. Levothyroxine is on the World Health Organization’s Model List of Essential Medicines and is inexpensive, yet access to blood tests for diagnosis and monitoring can be limited in rural areas. In such settings, clinical assessment, careful dosing and periodic testing where available can still provide effective care. Newborn screening for congenital hypothyroidism is standard in many high-income countries but not yet universal, and expanding it could prevent thousands of cases of avoidable disability every year.

Questions to ask your healthcare provider

• What is causing my thyroid problem?
• What are my TSH and free T4 results, and what is my target range?
• How and when should I take my medicine, and what should I avoid taking with it?
• How often will my blood be tested?
• What symptoms mean my dose may be too high or too low?
• What should I do if I become pregnant or plan a pregnancy?
• For hyperthyroidism: what are the pros and cons of tablets, radioactive iodine and surgery for me?
• Do I need any checks for my eyes, heart or bones?

Thyroid conditions, weight and exercise

Weight is one of the biggest concerns for people with thyroid conditions. In hypothyroidism, some weight gain is common, partly from fluid retention and partly from a slower metabolism. Once thyroid levels are corrected, some of this weight is usually lost, but treatment does not automatically lead to large weight loss, and many people are disappointed. In hyperthyroidism, weight loss is common before treatment, and many people regain weight, sometimes more than they lost, once their thyroid is controlled, partly because appetite remains high for a while.

The same principles of healthy weight management apply to people with and without thyroid conditions: regular meals based on vegetables, fruit, wholegrains, legumes and lean protein; limiting sugary drinks, refined carbohydrates and processed foods; and regular physical activity. Exercise is safe for people with treated thyroid conditions and improves energy, mood, heart health and bone strength. People with untreated or poorly controlled hyperthyroidism should avoid strenuous exercise until their heart rate is under control, as their heart is already working hard.

Travelling and daily routines

Levothyroxine is a once-daily medicine, which makes it relatively easy to manage, but routines can be disrupted by travel, shift work, fasting for religious observance and illness. Practical tips include:

• Keep your medicine in your hand luggage, with enough for the trip plus extra in case of delays.
• When crossing time zones, take your dose at the same local morning time; a few hours’ difference does not matter, because levothyroxine has a long half-life.
• If you miss a dose, take it when you remember the same day. If you remember the next day, many people can take two doses together, but check with your pharmacist first, particularly if you have heart disease.
• During fasting periods such as Ramadan, many people take levothyroxine at night, at least three to four hours after the last meal, or before the pre-dawn meal with enough time before eating. Discuss the best option with your healthcare provider.
• Night shift workers can take their dose at a consistent time relative to their sleep and meals, such as on waking.

Small inconsistencies are not dangerous, but regular routines give the most stable thyroid levels.

Living with thyroid eye disease

Thyroid eye disease can be one of the most distressing aspects of Graves’ disease, because changes in appearance and vision affect confidence, work and relationships. The active inflammatory phase usually lasts one to three years before settling into an inactive phase. Early specialist assessment, stopping smoking, keeping thyroid levels stable and protecting the eyes all improve outcomes. Once the disease is inactive, reconstructive procedures can correct remaining changes in many people. Patient support groups offer valuable practical and emotional support during this time.

Frequently asked questions

Is hypothyroidism permanent?

Hypothyroidism caused by Hashimoto’s, surgery or radioactive iodine is usually lifelong. Some forms, such as postpartum or other thyroiditis, can be temporary.

Can I take levothyroxine with coffee?

Coffee reduces absorption. Wait 30 to 60 minutes after taking levothyroxine before having coffee or breakfast.

Can thyroid problems cause anxiety or depression?

Yes. Hyperthyroidism can cause anxiety and restlessness, and hypothyroidism can cause low mood. Anyone with new mental health symptoms may benefit from a thyroid test.

Can men get thyroid disease?

Yes, though it is less common than in women. Men can develop all types of thyroid disorder.

Does thyroid disease affect fertility?

Both underactive and overactive thyroid can affect periods, ovulation and fertility. Treatment usually restores normal function.

Can I have children after radioactive iodine?

Yes. Pregnancy should be avoided for at least six months after treatment, and thyroid levels should be stable before conceiving.

But what if my tests are normal and I still feel exhausted?

Normal thyroid tests are reassuring, and it is important not to keep chasing a thyroid explanation. Persistent tiredness has many possible causes, including anaemia, vitamin deficiencies, diabetes, sleep apnoea, depression, anxiety, menopause, chronic infection, medicines and lifestyle factors. Ask your healthcare provider for a broader assessment rather than repeated thyroid tests or unregulated thyroid supplements. The right diagnosis is the first step to feeling better.

Related: Underactive vs overactive thyroid symptoms · Thyroid disorders: nursing care

Sources: World Health Organization and UNICEF (iodine deficiency and universal salt iodisation), American Thyroid Association guidelines, European Thyroid Association guidelines, National Institute for Health and Care Excellence (NICE) thyroid disease guideline, Endocrine Society clinical practice guidelines, European Group on Graves’ Orbitopathy (EUGOGO).