Iodine levels of iodine-131 is the chance occurrence of radiogenic thyroid cancer in later life. Other risks include the possibility of non-cancerous growths and thyroiditis. The usual means of protection against the negative effects of iodine-131 is by saturating the thyroid gland with stable iodine-127 in the form of potassium iodide tablets, taken daily for optimal prophylaxis. However, iodine-131 may also be used for medicinal purposes in radiation therapy for this very reason, when tissue destruction is desired after iodine uptake by the tissue. Iodine-131 is also used as a radioactive tracer. Though it is the least reactive of the halogens,
Lugol's iodine 126.5 mg/mL. The 15% solution thus has a total iodine content of 6.32 mg per drop of 0.05 mL; the 2% solution has 0.84 mg total iodine content per drop. Potassium iodide renders the elementary iodine soluble in water through the formation of the triiodide () ion. It is not to be confused with tincture of iodine solutions, which consist of elemental iodine, and iodide salts dissolved in water and alcohol. Lugol's solution contains no alcohol. Other names for Lugol's solution are (iodine-potassium iodide); Markodine, Strong solution (Systemic); and Aqueous Iodine Solution BP. In the United Kingdom the NHS pays