hypothyroid

Hypothyroid, or hypothyroidism, is a condition in which the thyroid gland does not produce enough thyroid hormones, mainly thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolism, energy use, temperature, and growth. When levels are low, many body systems slow down.

Most cases are due to primary hypothyroidism, where the thyroid itself is damaged or dysfunctional. Hashimoto's thyroiditis, an autoimmune condition, is the most common cause in iodine-sufficient regions. Other causes include iodine deficiency, thyroid removal or radiation, certain medications, and congenital defects.

Symptoms vary but commonly include fatigue, weight gain, cold intolerance, dry skin, constipation, hair thinning, and a slowed heart rate. Women are more commonly affected, and risk rises with age.

Diagnosis relies on laboratory testing. A high serum thyroid-stimulating hormone (TSH) with a low free thyroxine (T4) indicates primary hypothyroidism. Autoantibodies may be present in Hashimoto's. Imaging is not routinely required.

Treatment is typically lifelong thyroid hormone replacement, usually levothyroxine. Dosing is individualized and guided by TSH targets, often after several weeks. Take the medication on an empty stomach and avoid taking calcium, iron, or certain supplements at the same time.

Prognosis is good with appropriate treatment. Untreated hypothyroidism can lead to myxedema, cardiovascular problems, infertility, and cognitive impairment. Overreplacement can cause hyperthyroid symptoms and increased fracture risk, especially in older adults.

In pregnancy, thyroid hormone needs rise, and treatment goals are adjusted to maintain TSH within trimester-specific ranges to support fetal development.