WASHINGTON—U.S. health regulators on Wednesday finalized stronger warnings for breast implants, including a new requirement that people receive detailed information about their potential risks and complications before getting them. The Food and Drug Administration announced the new regulations mainly aimed at implant manufacturers, who are also being required to add a boxed warning message—the most serious type—to their written patient materials. The FDA requirements are the latest step in a decades-long effort to manage safety issues with the devices, which are primarily used for breast augmentation, the most common cosmetic surgical procedure in the U.S. Roughly 400,000 people get implants each year, 100,000 of them after cancer surgery. The FDA had originally proposed the rules as voluntary measures in 2019, but Wednesday’s action makes them legal requirements for breast implant makers, including leading manufacturers like Johnson & Johnson’s Mentor unit and Allergan. In the biggest shift, plastic surgeons and other …