The Thompsons (defendant), residents of Canada, and the MacTavishes, residents of Scotland, filed separate complaints against Merrell Dow Pharmaceuticals (Merrell Dow) (plaintiff) in Ohio state court. The complaints alleged that, because the mothers took a Merrell Dow product called Bendectin during pregnancy, their children were born with multiple deformities. The complaints were founded on five counts of common law state theories and one count based on a violation of the Federal Food, Drug, and Cosmetic Act (FDCA), because the drug may have been misbranded and lacked the requisite warning on its label. There is no federal cause of action for violations of the FDCA. Merrell Dow filed a petition for removal from state court, arguing such removal was justified under §1331. Once removed, the Thompsons’ and MacTavishes’ actions were consolidated. The Thompsons filed a motion to remand to the state court, and the district court denied the motion, holding that the count in the complaint based on an alleged violation of the FDCA was a cause of action arising under federal law. The United States Court of Appeals for the Sixth Circuit reversed, and the United States Supreme Court granted certiorari.