Overview
Hypothyroidism occurs when the thyroid gland produces insufficient thyroid hormone to meet the body's needs. Since thyroid hormones regulate metabolism, heart rate, body temperature, and many other functions, low levels cause a wide range of symptoms across multiple body systems. It is more common in women and older people, and is readily treatable with daily hormone replacement medication.
Causes and risk factors
The following factors are associated with the development of Hypothyroidism:
- Hashimoto's thyroiditis — autoimmune condition, most common cause
- Previous thyroid surgery or radioiodine treatment
- Certain medications: lithium, amiodarone
- Iodine deficiency
- Congenital hypothyroidism
- Pituitary gland disorders
- Radiation therapy to the neck
- Postpartum thyroiditis
Signs and symptoms
Common signs and symptoms of Hypothyroidism include:
- Fatigue and sluggishness
- Increased sensitivity to cold
- Constipation
- Pale, dry skin
- Puffy face
- Brittle nails and hair loss
- Unexplained weight gain
- Muscle weakness and aches
- Depression and slowed thinking
- Slow heart rate
- Heavy or irregular periods
- Elevated cholesterol
Diagnosis
Hypothyroidism is typically diagnosed through a combination of medical history, physical examination, and appropriate investigations such as blood tests, imaging, or specialist review, depending on the specific condition and presentation. Your doctor will consider all relevant symptoms and risk factors before making a diagnosis.
Treatment options
Treatment approaches for Hypothyroidism may include:
- Levothyroxine (synthetic T4) — daily replacement hormone
- Regular blood tests to monitor TSH and T4 levels
- Lifelong treatment usually required
- Liothyronine (T3) added in some cases
- Annual monitoring once stable
Prevention
Not generally preventable. Adequate iodine intake from dairy, seafood, and iodised salt is important. Regular checks for at-risk individuals.
Complications
If left untreated or poorly managed, Hypothyroidism can lead to complications including:
Heart problems including heart failure, nerve damage, myxoedema coma, infertility, birth defects, and goitre.
Sources and references: This article is written in accordance with NHS UK, WHO, and Mayo Clinic clinical guidelines. It is reviewed for accuracy by the SymptomSense content team. ICD-10 code: E03. Last reviewed June 2026.