US Challenge to Amgen Deal Threatens Big Pharma Business Model

US trade regulators’ surprise attempt to block a pending drug industry merger is creating alarm that the government will upend a successful business model in the industry.

Big, rich drugmakers often buy smaller companies or their drugs, using their heft to bring the medicines to lucrative markets. On Tuesday, the Federal Trade Commission filed a lawsuit to stop Amgen Inc. from buying Horizon Therapeutics Plc for $27.8 billion, what would be the company’s largest acquisition, citing the potential for Amgen to pressure buyers to pay high prices for Horizon’s drugs.

News of the impending suit leaked Monday, and analysts were ...