Walgreens slashed its 2019 forecast and missed second-quarter expectations with a performance that sent its shares plunging Tuesday and helped knock down the Dow Jones Industrial Average.

Company leaders told analysts that challenges they had been expecting like reimbursement cuts and lower price increases for branded drugs hit sooner than they anticipated.

“This has been a very disappointing quarter for us,” Executive Vice Chairman and CEO Stefano Pessina said after noting in a statement that it was the company’s most challenging quarter since it formed more than four years ago.

The nation’s largest drugstore chain said it now expects adjusted earnings per share to be roughly flat this year after confirming as recently as late December a forecast for growth of 7 percent to 12 percent.

Drugstores are facing stress from several angles.

There is growing pressure to cut prescription drug costs, and payers like insurers and pharmacy benefit managers are trimming their reimbursement. Generic drugs aren’t as profitable as they used to be. Stores also are changing what they sell in the retail areas outside their pharmacies to keep customers coming in the door instead of shopping online at sites like Amazon.com.

Plus Walgreens Chief Financial Officer James Kehoe said in late February that his company has been “quite damaged” by rival CVS Health Corp.’s acquisition of Aetna, one of the nation’s largest insurers. He noted that Aetna transferred significant business to CVS pharmacies.

Walgreens runs more than 18,500 stores in 11 countries after the Deerfield, Ill.-based drugstore chain combined at the end of 2014 with European health and beauty retailer Alliance Boots.