Thyroid underactive living in adults

Overview

An underactive thyroid, also called hypothyroidism, means your thyroid gland does not make enough thyroid hormone. This hormone controls how your body uses energy. When levels are too low, many functions slow down.

Yes. It affects about 2 in 100 people in the UK, and it's more common as you get older.

It can affect anyone, but it is much more common in women. People over 60 and those with a family history of thyroid problems are at higher risk.

Symptoms

Common symptoms

• Feeling very tired and lacking energy
• Unexplained weight gain
• Feeling cold when others are warm
• Dry skin and hair
• Constipation (trouble pooing)
• Depression or low mood
• Slow heart rate
• Muscle aches and weakness
• Poor concentration or memory issues

Symptoms in older adults

• Memory problems that can look like dementia
• Falls due to muscle weakness or slow reflexes
• Increased sensitivity to cold
• Hoarse voice and slower movements

Causes

Main causes

• An autoimmune condition called Hashimoto's disease – your immune system attacks your thyroid by mistake
• Treatment for an overactive thyroid (such as radioactive iodine or surgery)
• Thyroid surgery to remove part or all of the gland
• Radiation therapy to the neck area for cancer
• Certain medicines (e.g., lithium, amiodarone) – talk to your doctor about risks

Risk factors

• Being female
• Being over 60 years old
• Having a family history of thyroid problems
• Having another autoimmune disease (like type 1 diabetes, coeliac disease, or rheumatoid arthritis)
• Having had a previous pregnancy (postpartum thyroiditis is temporary in some women)

When to see a doctor

See a doctor urgently if:

• You have symptoms that worry you suddenly, like chest pain or confusion
• After thyroid surgery or radioactive iodine treatment, if you have symptoms of hypothyroidism

Book a routine appointment if:

• You have several symptoms listed above that last for a few weeks
• You have a family history of thyroid problems and feel unwell
• You are a woman over 60 and have tiredness, weight gain, or feeling cold

Diagnosis

Your doctor will talk with you about your symptoms and check your neck for swelling. The main way to diagnose it is with a blood test that measures thyroid hormone levels.

Tests that may be done

• Thyroid function test (TSH – thyroid stimulating hormone) – high levels mean your thyroid is underactive
• Free T4 (thyroxine) test – low levels confirm hypothyroidism
• Thyroid antibodies test – to check for an autoimmune cause like Hashimoto's disease

What to expect at your appointment

The blood test is quick and done at your GP surgery or local clinic. Results usually come back in a few days to a week. Your doctor will explain the results and what they mean for you.

Treatment

The standard treatment is taking a thyroid hormone replacement medicine every day. This medicine replaces the hormone your thyroid is not making. It is usually taken once a day on an empty stomach, at the same time each day. The dose is adjusted based on your blood test results.

Self-care at home

• Take your medicine exactly as prescribed – never skip doses or change the amount yourself
• Set a daily reminder to take your tablet at the same time each morning
• Keep your tablets away from heat and moisture
• If you miss a dose, take it as soon as you remember, but skip it if it's almost time for your next dose – never double up

Medical treatments

The main treatment is a synthetic form of the thyroid hormone thyroxine, taken as a small tablet once a day. The dose is individualised and monitored with regular blood tests (every 6 to 12 months once stable). Some people may need a different form of hormone if the standard one doesn't suit them. Your doctor will decide the best option for you.

When is surgery considered?

Surgery is not used to treat hypothyroidism itself. However, if you had thyroid surgery for another reason (like cancer or an overactive thyroid), you will need lifelong hormone replacement therapy.

Living with this condition

Most people with hypothyroidism live a normal, active life once their medicine dose is correct. You will need regular check-ups with your doctor and blood tests. Some days you may feel more tired – that's okay. Adjust your activities to what your body tells you.

Lifestyle tips

• Take your medicine every day without fail – it's the key to feeling well
• Get enough sleep – 7 to 9 hours a night can help energy levels
• Manage stress with relaxation techniques like deep breathing or gentle walks
• Avoid large changes in diet, especially around taking your medicine

Diet and exercise

A healthy, balanced diet is important. Eat plenty of fruits, vegetables, whole grains, and lean protein. Some foods (like soy, high-fibre foods, and iron or calcium supplements) can affect how your thyroid medicine is absorbed. Take your medicine on an empty stomach and wait at least 30 minutes before eating or taking other supplements. Gentle exercise like walking, swimming, or yoga can help with energy and mood – start slowly and build up.

Mental health and emotional wellbeing

Hypothyroidism can cause depression, anxiety, or brain fog. If you notice low mood or worry, it's important to talk to your doctor – adjusting your medicine dose may help. If you are having thoughts of harming yourself or feel in crisis, contact emergency services or a crisis helpline immediately. You are not alone.

Prevention

Most cases of hypothyroidism cannot be prevented because they are caused by an autoimmune condition or previous treatment. However, early diagnosis and proper treatment prevent complications.

Screening programmes

Routine screening for hypothyroidism is not recommended for everyone. However, if you have risk factors (like a family history or another autoimmune disease), your doctor may check your thyroid levels as part of your regular care.

Complications

If left untreated

• Severe tiredness and weakness
• Heart problems, including a slow heartbeat or heart failure
• High cholesterol, which increases risk of heart disease
• Myxedema coma – a rare but life-threatening condition where the body slows down dangerously
• Depression and cognitive difficulties
• Infertility or problems during pregnancy (for women)

Long-term outlook

With proper treatment, the outlook is excellent. Most people feel back to normal within a few weeks to months of starting medicine. Lifelong monitoring is needed, but you can live a full, healthy life.

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