Potassium iodide is used to loosen and break up mucus in the airways. This helps you couch up the mucus so you can breathe more easily if you have long-term lung problems (ex: asthma, chronic bronchitis, emphysema). This medication is known as an expectorant.
Potassium iodide is also used along with anti-thyroid medicines to prepare the thyroid gland for surgical removal, to treat certain overactive thyroid conditions (hyperthyroidism), and to protect the thyroid in a radiation exposure emergency. It works by shrinking the size of the thyroid gland and decreasing the amount of thyroid hormones produced.
In a radiation emergency, potassium iodide blocks only the thyroid from absorbing radioactive iodine, protecting it from damage and reducing the risk of thyroid cancer.