Aug. 6 (Bloomberg) — Walgreen Co., the biggest U.S. drugstore chain, said it plans to buy all of Alliance Boots for about $15.3 billion and won't use the deal to move its tax address abroad.

Walgreen already owns 45 percent of Bern, Switzerland-based Boots, which has pharmacy and beauty stores in Europe. It will pay about $5.29 billion in cash and $10 billion in Walgreen stock for the remaining stake, the company said today in a statement. The stock fell 9.2 percent to $62.75 at 7:10 a.m. in New York trading.

Walgreen will remain based near Chicago. The company had previously considered moving its headquarters as a way to lower the rate it pays the U.S. government. The U.S. pharmacy chain has come under political pressure not to do a so-called tax inversion as other health companies, including drugmakers AbbVie Inc. and Pfizer Inc., struck or attempted deals to cut their own rates and leave the U.S.