Eli Lilly & Co.’s shares saw the biggest one-day drop since 2008 after CVS Health Corp. announced a plan to drop its blockbuster weight-loss drug Zepbound from its preferred list, making rival Wegovy more widely available.

Eli Lilly on Thursday downplayed CVS Health's decision to drop the company's obesity drug Zepbound from some lists of medicines it covers for reimbursement, but shares of the drugmaker still fell roughly 10% on investor worries that the move could blunt its sales momentum.

Adding to the pressure is that CVS Health has retained coverage of Zepbound's arch rival Wegovy (semaglutide), sold by Novo Nordisk, after negotiating a price cut with the company, along with Novo Nordisk's newly forged alliances with three leading telehealth companies to drive self-pay sales of its weight loss drug.