Gladys Mensing and Julie Demahy (plaintiffs) filed separate suits in federal district courts against Pliva, Inc. (Pliva) and other manufacturers (defendants) of a generic drug for metoclopramide, claiming defendants failed to provide adequate warning labels for the drug. Metoclopramide was a drug designed to speed the movement of food through a person’s digestive system and to treat digestive tract problems such as diabetic gastroparesis and gastroesophageal reflux disorder. The Food and Drug Administration (FDA) first approved metoclopramide tablets under the brand name Reglan in 1980. Five years later, generic manufacturers, including defendants, began making the drug. Warning labels for the drug consistently changed over the years, the most recent of which warned individuals that tardive dyskinesia, a serious and often irreversible movement disorder, could develop in patients treated with metoclopramide. After taking the drug for several years, plaintiffs developed tardive dyskinesia. In both actions defendants maintained that federal law pre-empted the plaintiffs’ state tort claims. More specifically, defendants claimed that federal statutes and FDA regulations required it to use the same safety and efficacy labeling on the generic versions of the drug as their brand-name counterparts. The lawsuits were consolidated. The courts of appeal for the Fifth and Eighth Circuits concluded that plaintiffs’ claims were not pre-empted by federal law. Defendants appealed. The U.S. Supreme Court granted certiorari to review.