CVS Health said it will significantly expand access to Novo Nordisk's blockbuster weight loss drug Wegovy for patients covered by its pharmacy benefit manager, Caremark. Starting July 1, Caremark will prioritize Wegovy on its standard formularies — or lists of covered drugs — making it the preferred GLP-1 drug for obesity.

The deal could expand access to its in-demand obesity drug at the expense of Eli Lilly, whose shares fell by double digits on Thursday.

Investors are worried Novo Nordisk's competition with Eli Lilly is heating up and that the first-to-market GLP-1 leader is losing ground.