than 2550 barbiturates and related compounds have been synthesised, with 50 to 55 in clinical use around the world at present. The first to be used in medicine was barbital (Veronal) starting in 1903, and the second, phenobarbital was first marketed in 1912. Barbituric acid is a chemical building block in the laboratory synthesis of riboflavin (vitamin B2) and in a method of producing the pharmaceutical drug minoxidil. It is one of the four ingredients in the synthesis of riboflavin. Before barbituric acid was substituted in the synthesis of riboflavin, it was too expensive to synthesize riboflavin. According to Taber's Cyclopedic Medical Dictionary, overdoses cause respiratory depression, cyanosis, circulatory collapse, stupor, coma, and possibly death. Health and safety Overdose of barbiturate drugs can cause respiratory depression and death. Barbiturates are dependence-producing, and abrupt cessation of high doses can result in a very medically serious, even lethal, withdrawal syndrome. Barbituric acid derivatives are considered DEA Schedule III controlled substances. See also Barbiturase Thiobarbituric acid Isocyanuric acid References External links Barbiturates Pyrimidines 1864 in science