Acetanilide is a synthetic organic compound introduced clinically in 1886 as a fever-reducing drug. Its effectiveness in relieving pain was discovered soon thereafter and it was used as an alternative to aspirin for many years in treating such common complaints as headaches, menstrual cramps, and rheumatism. Unfortunately, Acetanilide exhibited an unacceptable profile of toxic effects, the most alarming being cyanosis due to methemoglobinemia. The toxic profile prompted the search for supposedly less toxic aniline derivatives such as phenacetin. After several conflicting results over the ensuing fifty years, it was established in 1948 that acetanilide was mostly metabolized to paracetamol (USAN: acetaminophen) in the human body and that it was the paracetamol that was responsible for the analgesic and antipyretic properties. Paracetamol has since replaced acetanilide usage because it is less likely to induce blood disorders. The observed methemoglobinemia after acetanilide administration was ascribed to the small proportion of acetanilide that is hydrolyzed to aniline in the body. Acetanilide is no longer used as a drug in its own right, although its primary metabolite, paracetamol, has been widely succesful.