Metamizole, a nonnarcotic analgesic, has been used to treat pain and fever for almost 90 years in some countries, while in others it is completely unknown or forgotten. It was synthesized by the German company Hoechst AG in 1920, and its mass production started in 1922. Metamizole remained freely available worldwide until the 1970s, when it was found that the drug poses a risk of causing agranulocytosis. Soon after that, metamizole was banned in the United States, Japan, Australia, and part of the European Union. However it is still widely used in some European countries, Turkey, Israel, India, Brazil, and Third World countries. Metamizole is available over-the-counter and remains one of the most popular analgesics in Bulgaria. The objective of this study is to review the pharmaceutical and pharmaco-toxicological aspects of the drug. In Part II, the clinical profile of the drug will be discussed.