Pfizer filed suit in Delaware’s Court of Chancery against Metsera and Novo Nordisk to stop Novo’s unsolicited takeover approach and enforce a September buyout agreement, the companies announced Friday. Pfizer alleges Metsera’s board and Novo breached the merger pact and fiduciary duties by treating Novo’s offer as a “superior proposal” and seeks an injunction to prevent Metsera terminating the Pfizer deal. The complaint centers on Novo’s structurally unusual offer—a large upfront cash payment tied to half the company’s equity—that Pfizer says is designed to sidestep antitrust scrutiny and is not reasonably likely to close. Pfizer argues Metsera rejected a similar proposal earlier for regulatory risk; Novo then made the bid public, prompting Metsera to reopen talks. The dispute matters to obesity-drug markets and M&A strategy: Metsera’s pipeline includes next-generation weight-loss candidates that big pharma views as fast routes into the competitive GLP-1 and amylin-driven obesity market. The litigation raises the prospect of a rapid, high-stakes court decision that could determine which buyer secures priority access to Metsera’s assets.