Walgreen (WAG) is the first drugstore chain to post May sales, and if the company's results are any indication of what lies ahead, it's not promising.

The company reported a 1% increase in May same-store sales, but missed analysts' expectations of a 2.2% jump.

Pharmacy comparable sales rose just 1.5%, hurt by the introduction of generic drugs this year. Analysts predicted a 3.5% rise in this segment.

Prescriptions filled on a same-store basis rose 2.8%.

Pharmacy sales accounted for 65% of total sales.

Total monthly sales rose 6.1% to $5.37 billion. Sales in 2009 are up 7.2% to $47.64 billion, while same-store sales for the year-to-date period rose 1.9%.

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Walgreen opened 43 stores in May, including four relocations and the acquisition of 38 stores. The company closed three stores.

Shares of the company were up by a little more than 1% to $31.56 in morning trading. By comparison, its rival

Rite Aid

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saw its shares soar more than 12% to $1.46, continuing the upward trend that the stock has seen since mid-March.

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