The two companies reached a new agreement in July after a series of disputes that resulted in the discontinuation of their prior contract. Walgreen resumes filling prescriptions from customers in the Express Scripts network this month.

Pharmacy sales — which made up a majority of total sales in August — fell 7.2 percent during the month. Pharmacy sales at stores open at least a year declined 12.4 percent. The company said that these sales were hurt by generic drug introductions over the past year and by not being part of the Express Scripts network.

Revenue at stores open at least a year dropped 8.2 percent, pulled down by the generic drug introductions.

The figure is an important gauge of a retailer's health, because it measures growth at existing location and excludes the impact of stores that opened or closed during the year.

Customer traffic at stores open at least a year fell 2.2 percent during the month, but the amount of items shoppers bought rose 1.6 percent.

For the fourth quarter, revenue fell 5 percent to $17.08 billion, with revenue at stores open at least a year down 8.7 percent.

Analysts, on average, expected quarterly revenue of $17.2 billion, according to FactSet.

Prescriptions filled at stores open at least a year declined 8 percent in the fourth quarter, while pharmacy sales at these stores dropped 12.6 percent.

Fiscal 2012 revenue edged down less than 1 percent to $71.64 billion, with revenue at stores open at least a year off 3.6 percent.

Walgreen, which announced last week that it will launch its first ever customer rewards program in September, had 8,386 locations in the 50 states, the District of Columbia, Puerto Rico and Guam as of Aug. 31. This includes 7,929 drugstores.