Competitors have also been aggressively promoting their loyalty programs and offering steep discounts in a bid to retain the Express Scripts users they gained and this would make it tough for the company to quickly regain their ex-customers.

FORBES: Walgreen Can Reach $38 As Express Scripts Customers Return

Pharmacists have also been hit hard by cuts in reimbursement from state Medicaid programs for the poor and are getting squeezed by larger pharmacy benefit managers like Express Scripts (ESRX) who pay pharmacies to dispense drugs for their employer clients.

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