The dimercaptosuccinic acid (DMSA) is a drug used in the chelation therapy to treat arsenic, lead, and mercury poisoning. It is usually adminestered intravenously, but also orally. In the blood stream, the DMSA ions bind to the contaminating metal, which is then rapidly excreted with the urine through the kidney. It is a colorless substance. Chemically, it has two carboxylic acid and two thiol groups.