Walgreens cut ties with the pharmacy benefits manager on December 31st, saying it wasn't getting a fair reimbursement from Express Scripts. The two companies had been feuding publicly for months.
It's estimated that Walgreens filled 80 million prescriptions for Express Scripts through the end of August 2011.
Competing drug store chains have been advertising heavily promoting their acceptance of Express Scripts to snare Walgreens customers. Walgreens has countered by reducing the price of its prescription savings club. Company officials say a record 200,000 customers joined it this month.
Express Scripts has announced plans to merge with Medco, another pharmacy benefits administrator.