Iodine-131 is a radioactive isotope of iodine that is commonly used in medicine, particularly for treating thyroid conditions. It emits radiation that can help destroy overactive thyroid cells, making it effective for conditions like hyperthyroidism and certain types of thyroid cancer. Patients typically take it in a capsule or liquid form, and it is absorbed by the thyroid gland. This isotope has a relatively short half-life of about eight days, meaning it loses its radioactivity quickly. Because of this, it is considered safe for use in medical treatments, as the body eliminates it within a few weeks.