Air will oxidize iodide, as evidenced by the observation of a purple extract when aged samples of KI are rinsed with dichloromethane. As formed under acidic conditions, hydriodic acid (HI) is a stronger reducing agent.Like other iodide salts, KI forms triiodide (I−3) when combined with elemental iodine.
A likely lethal dose of salt (more than a kilogram) would be needed to equal the potassium iodide in one tablet.The World Health Organization does not recommend KI prophylaxis for adults over 40 years, unless the radiation dose from inhaled radioiodine is expected to threaten thyroid function, because the KI side effects increase with age and may exceed the KI protective effects; "...unless doses to the thyroid from inhalation rise to levels threatening thyroid function, that is of the order of about 5 Gy. Such radiation doses will not occur far away from an accident site. "The U.S. Department of Health and Human Services restated these two years later as "The downward KI (potassium iodide) dose adjustment by age group, based on body size considerations, adheres to the principle of minimum effective dose. The recommended standard (daily) dose of KI for all school-age children is the same (65 mg). However, adolescents approaching adult size (i.e., >70 kg [154 lbs]) should receive the full adult dose (130 mg) for maximal block of thyroid radioiodine uptake. Neonates ideally should receive the lowest dose (16 mg) of KI. "SSKI (i.e., the "saturated solution of KI" rather than tablets) may be used in radioiodine-contamination emergencies (i.e., nuclear accidents) to "block" the thyroids uptake of radioiodine, at a dose of two drops of SSKI per day for an adult.