Thyroid Health2 in 100 people in the UK

Hypothyroidism

Also known as: Underactive Thyroid, Low Thyroid

Hypothyroidism is a condition where the thyroid gland doesn't produce enough thyroid hormones, causing your metabolism to slow down. It's common, treatable, and affects about 2% of people in the UK.

Last reviewed: 15 January 2026

What is Hypothyroidism?

The thyroid is a small, butterfly-shaped gland in your neck that produces hormones controlling how your body uses energy. When it's underactive, every system in your body slows down. Women are 5-10 times more likely to develop hypothyroidism than men.

Who is affected?

Most common in women over 60, but can affect anyone. Risk increases with age and family history of thyroid problems.

Symptoms of Hypothyroidism

Common Symptoms

  • Tiredness and fatigue
  • Weight gain
  • Feeling cold when others don't
  • Dry skin and hair
  • Constipation
  • Depression or low mood
  • Difficulty concentrating
  • Muscle aches and weakness

Less Common Symptoms

  • Slow heart rate
  • Hoarse voice
  • Puffy face
  • Thinning hair or hair loss
  • Heavy or irregular periods
  • Fertility problems
  • Carpal tunnel syndrome

When to Seek Urgent Help

  • Myxoedema (severe swelling)
  • Heart problems
  • Mental health issues
  • Myxoedema coma (medical emergency)

Causes & Risk Factors

Causes

  • Hashimoto's thyroiditis (autoimmune condition - most common cause)
  • Treatment for hyperthyroidism (radioactive iodine or surgery)
  • Thyroid surgery
  • Radiation therapy to the head or neck
  • Certain medications (lithium, amiodarone)
  • Iodine deficiency (rare in the UK)
  • Pituitary gland problems

Risk Factors

  • Being female
  • Age over 60
  • Family history of thyroid disease
  • Having an autoimmune condition
  • Previous thyroid problems or treatment
  • Pregnancy (especially recent)
  • Turner syndrome or Down syndrome

Possible Complications if Untreated

  • Heart problems (high cholesterol, enlarged heart)
  • Mental health issues
  • Peripheral neuropathy
  • Infertility
  • Birth defects if untreated during pregnancy
  • Goitre (enlarged thyroid)

Diagnosis & Blood Tests

Hypothyroidism is diagnosed through blood tests measuring thyroid hormone levels. A raised TSH with low T4 confirms the diagnosis.

TSH (Thyroid Stimulating Hormone)

The first-line test for thyroid function. High TSH suggests underactive thyroid.

What to look for: Normal range is typically 0.4-4.0 mU/L. Higher values indicate hypothyroidism.

Free T4 (Thyroxine)

Measures the active thyroid hormone in your blood.

What to look for: Low T4 with high TSH confirms hypothyroidism.

Thyroid Antibodies

Tests for TPO and TgAb antibodies to check for autoimmune thyroid disease.

What to look for: Positive antibodies suggest Hashimoto's thyroiditis.

Free T3 (Triiodothyronine)

Sometimes tested to get a fuller picture of thyroid function.

What to look for: The most active form of thyroid hormone.

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Treatment Options

Treatment involves taking a daily thyroid hormone replacement tablet (levothyroxine) to restore normal hormone levels.

  • Levothyroxine (synthetic T4) - the standard treatment
  • Regular blood tests to monitor and adjust dose
  • Lifelong treatment is usually needed
  • Take medication on an empty stomach, 30-60 minutes before food

Living with Hypothyroidism

  • Take your medication at the same time every day, preferably in the morning
  • Wait at least 30 minutes before eating or drinking (except water)
  • Keep your regular blood test appointments
  • Be aware that some supplements can interfere with absorption
  • Exercise regularly to help manage weight and mood
  • Eat a balanced diet with adequate iodine

Frequently Asked Questions

Will I need to take medication forever?

In most cases, yes. Hypothyroidism is usually a lifelong condition requiring ongoing treatment. However, some cases (like those caused by pregnancy) may resolve.

Can diet cure hypothyroidism?

No, diet alone cannot cure hypothyroidism. You need medication to replace the missing thyroid hormones. However, a healthy diet supports overall wellbeing.

Can I exercise with hypothyroidism?

Yes, and it's encouraged! Exercise can help manage weight, improve mood, and boost energy. Start slowly and build up gradually.

What foods should I avoid?

Take medication away from soy products, high-fibre foods, and calcium supplements as they can affect absorption. Otherwise, eat a normal balanced diet.

When to See Your GP

  • Persistent tiredness that doesn't improve with rest
  • Unexplained weight gain
  • Feeling cold all the time
  • Changes in your menstrual cycle
  • Depression or mood changes
  • Constipation that doesn't respond to treatment
  • You have risk factors and symptoms
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