Opium: An addictive narcotic drug that is derived from the unripe seedpods of the opium poppy. Preparations of opium were called laudanum. Derivatives of opium include paregoric (a drug used to treat diarrhea), morphine, and heroin. For centuries, opium was used as a painkiller in the Middle East and Asia. It gained great popularity in Europe and the European colonies in the 18th century and became a main ingredient in patent medicines that patients could easily obtain without prescriptions. Many people became addicted to opium. Wounded Civil War soldiers who were in pain often received morphine. By 1900, it is estimated that more than 200,000 people in the US were addicted to opium and its derivatives. In 1909, the US Congress passed a law prohibiting the manufacture and sale of opium.