Known causes include Intrinsic thyroid hormone production defects Ingestion of foods that contain substances that inhibit thyroid hormone synthesis (goitrogens, eg, cassava, broccoli, cauliflower, cabbage), as may occur in countries in which iodine deficiency is common Drugs that can decrease the synthesis of thyroid hormone (eg, amiodarone or other iodine-containing compounds, lithium) Iodine deficiency is rare in North America but remains the most common cause of goiter worldwide (termed endemic goiter).