Walgreens has agreed to pay $6.7 billion in cash and stock to acquire a 45 percent stake in European pharmacy retailer Alliance Boots.

The deal, which calls for Walgreens to pay $4 billion in cash and 83.4 million shares, also provides an option for the U.S. drug store chain to purchase the remaining 55 percent stake in Alliance Boots in 2015 for approximately $9.5 billion in cash and stock.