NHS information · Neck

Worried about underactive thyroid?

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This page summarises publicly available NHS information for educational purposes only. It is not medical advice or a diagnosis. Always consult a qualified healthcare professional.

What is underactive thyroid?

An underactive thyroid (hypothyroidism) means the thyroid gland doesn't produce enough hormones, slowing down many body functions. Symptoms include extreme tiredness, weight gain, feeling cold, constipation, low mood, and difficulty concentrating. It's most often caused by an autoimmune condition called Hashimoto's disease. Treatment with daily levothyroxine tablets is usually lifelong and very effective.

When NHS resources suggest seeing a GP

  • You feel extremely tired and can't explain why.
  • You're gaining weight without eating more than usual.
  • You feel cold more than other people around you.
  • You feel low, depressed, or have difficulty concentrating.
  • You have constipation that isn't improving with diet changes.
  • You have a family history of thyroid or autoimmune conditions.
  • You're pregnant or planning pregnancy and have thyroid symptoms.
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Self-care information from NHS

  • Take levothyroxine at the same time every day, ideally on an empty stomach before breakfast.
  • Attend regular blood tests to check your thyroid levels — the dose may need adjusting.
  • Don't stop or change your dose without speaking to a GP.
  • Tell your GP or midwife if you're pregnant — your dose usually needs increasing.
  • Some supplements (calcium, iron) and foods (soya) can interfere with absorption — take them at least 4 hours apart.
  • Exercise regularly and eat a balanced diet to help manage weight and energy levels.

Common questions

Is hypothyroidism serious?

An underactive thyroid is not usually serious if treated. Levothyroxine replaces the missing hormone and most people feel well on the right dose. Untreated, it can lead to heart problems, high cholesterol, and in rare cases a life-threatening condition called myxoedema coma.

Will I need medication for life?

Usually yes — most people take levothyroxine for the rest of their life. The good news is it's a very effective, well-tolerated tablet with few side effects when the dose is right. Regular blood tests ensure you stay on the correct dose.

What causes an underactive thyroid?

The most common cause in the UK is Hashimoto's disease, an autoimmune condition where the immune system attacks the thyroid. Other causes include thyroid surgery, radiotherapy, and certain medications. It's more common in women and usually starts between ages 30 and 50.

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This page is for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional about your individual situation. NorMed organises publicly available NHS information and is not affiliated with the NHS.