Summary

Hypothyroidism is low thyroid hormone. Most cases are autoimmune Hashimoto_thyroiditis, a form of primary_hypothyroidism. Less often it is secondary_hypothyroidism from pituitary disease. Common symptoms include fatigue, cold intolerance, weight gain, constipation, dry skin, and bradycardia. Labs in primary show high TSH and low free_T4. Secondary shows low or normal TSH with low free_T4. Usual treatment is levothyroxine. Risk factors include female sex, older age, thyroid surgery, neck radiation, and drugs such as amiodarone or lithium.