Just as too little iodine can cause thyroid disease, so may prolonged intake of too much iodine lead to the development of goiter (swelling of the thyroid gland) and hypothyroidism (abnormally low thyroid activity).

Certain foods and medications contain large amounts of iodine. Examples include seaweed; iodine-rich expectorants (such as SSKI and Lugol's solution) used in the treatment of cough, asthma, chronic pulmonary disease; and amiodarone (CARDORONE), an iodine-rich medication used in the control of abnormal heart rhythms (cardiac arrhythmias).