Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormone. Thyroid hormone controls metabolism, energy, body temperature and many other functions, so even mild deficiency can produce noticeable symptoms.
It is one of the most common endocrine disorders worldwide and is usually manageable with hormone replacement once correctly diagnosed.
Last medically reviewed: 1 November 2025
Key points
- Hypothyroidism means the thyroid produces too little hormone.
- Common causes include Hashimoto’s thyroiditis and previous thyroid treatment.
- Symptoms include fatigue, weight gain, cold intolerance and constipation.
- Treatment is levothyroxine, monitored with TSH blood tests.
What causes hypothyroidism?
The most common cause in iodine-sufficient regions is Hashimoto’s thyroiditis, an autoimmune condition in which the immune system gradually damages the thyroid. Other causes include previous thyroid surgery or radioactive iodine treatment, certain medications (such as lithium or amiodarone), pituitary disorders, and, in some parts of the world, iodine deficiency.
Risk factors include being female, older age, a family history of thyroid or autoimmune disease, and having other autoimmune conditions such as type 1 diabetes or coeliac disease.
What are the symptoms?
Common symptoms include persistent fatigue, weight gain or difficulty losing weight, feeling cold, constipation, dry skin, hair thinning, muscle aches, low mood, poor concentration and heavier or irregular periods. Symptoms often develop slowly over months or years and are easily mistaken for stress or ageing.
Because symptoms are non-specific, a blood test — not symptoms alone — is required for diagnosis.
How is it diagnosed?
Diagnosis typically begins with a TSH (thyroid-stimulating hormone) blood test. An elevated TSH usually indicates the pituitary is working harder to stimulate an underactive thyroid. A free T4 test confirms whether hormone levels are low. Anti-TPO antibodies help identify autoimmune (Hashimoto’s) disease.
Subclinical hypothyroidism — elevated TSH with normal free T4 — may not need immediate treatment but should be monitored, especially in pregnancy, older adults, or when symptoms are present.
How is hypothyroidism treated?
Standard treatment is daily levothyroxine, a synthetic version of the T T 4 hormone the thyroid normally produces. It is taken on an empty stomach, usually 30–60 minutes before breakfast, and consistently at the same time each day. Dosing is individualised and guided by repeat TSH testing.
Most patients feel better within weeks of starting treatment, though full benefit can take several months. Lifelong treatment is usually required for primary hypothyroidism. Regular monitoring ensures the dose remains correct as weight, age and other medications change.
Frequently asked questions
Is hypothyroidism permanent?
In most cases, yes — primary hypothyroidism usually requires lifelong levothyroxine. Some cases caused by temporary thyroiditis or medication effects may resolve, but this is decided by your doctor through repeat testing.
Can hypothyroidism be cured with diet or supplements?
No. Hypothyroidism is a hormone deficiency that cannot be corrected by diet alone. Iodine only helps in iodine-deficiency-related cases. Levothyroxine is the established, evidence-based treatment; any supplements should be discussed with your clinician first.
How often should TSH be checked?
After starting or changing levothyroxine, TSH is usually rechecked every 6–8 weeks until stable, then roughly every 6–12 months. Your doctor will advise a schedule based on your situation.
What happens if hypothyroidism is left untreated?
Untreated hypothyroidism can worsen symptoms and, over time, contribute to high cholesterol, heart problems, fertility issues and, rarely, a serious condition called myxoedema coma. Prompt diagnosis and treatment prevent these complications.
References & further reading
This page is based on established medical knowledge and guidelines from authoritative sources. Always consult a qualified clinician for personal medical advice.
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