Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone. Because thyroid hormones help regulate metabolism and many body functions, symptoms can affect energy, temperature regulation, digestion, skin, mood and the cardiovascular system.
Common symptoms
- Fatigue and reduced energy
- Feeling unusually cold
- Weight gain
- Constipation
- Dry skin or hair changes
- Muscle aches or weakness
- Slower heart rate
- Heavy or irregular menstrual periods
- Difficulty concentrating or low mood
Diagnosis
Blood tests measuring thyroid-stimulating hormone (TSH) and free thyroxine (free T4) are central to diagnosis. Additional testing may help identify autoimmune thyroid disease or another underlying cause.
Treatment
Hypothyroidism is usually treated with levothyroxine, a synthetic form of thyroid hormone. The dose is individualized and monitored with blood tests. Treatment needs can change during pregnancy, with major weight changes, aging or use of certain medicines.
When to seek medical care
Persistent symptoms should be assessed rather than treated with thyroid supplements without testing. Severe untreated hypothyroidism can rarely become a medical emergency, particularly when there is marked drowsiness, confusion, low body temperature or breathing difficulty.
Sources and further reading
Last reviewed: 4 September 2026. This page provides general health information and does not replace individual medical assessment or treatment.