Eli Lilly's stock experienced a significant pre-market plunge of 5.07% on Thursday, as negative sentiment swept through the weight-loss drug sector following disappointing guidance from a key competitor.

The sharp decline came despite multiple analyst upgrades for Eli Lilly, with firms including Goldman Sachs, JP Morgan, Morgan Stanley, and Wells Fargo all raising their price targets on the pharmaceutical company following its strong fourth-quarter earnings report.

The sector-wide pressure appears to stem from Novo Nordisk's disappointing outlook for the year ahead, which caused its shares to tumble 19% at the opening bell in Copenhagen. As a major competitor to Eli Lilly in the GLP-1 weight-loss drug market, Novo Nordisk's guidance disappointment has raised concerns about the broader weight-loss drug sector, overshadowing Eli Lilly's own positive results and analyst upgrades.