KI
            
              
                (
                aq
                )
              
            
            
              
            
          
          

          
          +
          
            I
            
              2
              
                (
                s
                )
              
            
            
              
            
          
          ⟶
          
            KI
            
              3
              
                (
                aq
                )
              
            
            
              
            
          
        
      
    
    {\displaystyle {\ce {KI_{(aq)}{}+ I2_{(s)}-> KI3_{(aq)}}}}
  Unlike I2, I−3 salts can be highly water-soluble.
This is not the same as blocking the thyroids release of thyroid hormone, for which the adult dose is different (and is actually higher by a factor of 7 or 8), and for which KI anti-radiation pills (not a common medical treatment form of KI) are not usually available in pharmacies, or normally used in hospitals, or by physicians. Although the two forms of potassium iodide are completely interchangeable, normally in practice the SSKI solution, which is the historical medical form of high dose iodine, is generally used for all medical purposes save for radioiodine prophylaxis. For protection of the thyroid against radioiodine (iodine-131) contamination, the convenient standard 130 mg KI pill is used, if available. As noted, the equivalent two drops of SSKI (equaling the dose of one KI pill) may be used for this purpose, if the pills are not available. Side effects
There is reason for caution with prescribing the ingestion of high doses of potassium iodide and iodate, because their unnecessary use can cause conditions such as the Jod-Basedow phenomena, trigger and/or worsen hyperthyroidism and hypothyroidism, and then cause temporary or even permanent thyroid conditions. It can also cause sialadenitis (an inflammation of the salivary gland), gastrointestinal disturbances, and rashes.