orphan drug, drug developed under the U.S. Orphan Drug Act (1983) to treat a disease that affects fewer than 200,000 people in the United States. The orphan drug law offers tax breaks and a seven-year monopoly on drug sales to induce companies to undertake the development and manufacturing of such drugs, which otherwise might not be profitable because of the small potential market. (Of the 5,000 diseases covered under the act, 47% affect fewer than 25,000 people.) The law has led to the introduction of valuable new drugs for the treatment of rare diseases, but some drug companies have been accused of abusing the law's provisions by making inordinately high profits on orphan drugs under monopoly. Since the 1983 act went into effect, many orphan drugs have been approved, including those for the treatment of such conditions as AIDS, cystic fibrosis, blepharospasm (uncontrolled rapid blinking), and snake bite.