Prussian blue was originally developed as a dye for use in paints and ink. It is used in medicine to help speed up the body's elimination of certain metals or chemical elements. It works by binding to the metals in the digestive tract to keep the body from absorbing them. Prussian blue is used to treat people who have been contaminated with radioactive cesium or thallium, or non-radioactive thallium. Prussian blue may also be used for other purposes not listed in this medication guide.