Walgreens will acquire nearly 2,000 Rite Aid locations by the end of next spring.

CHICAGO—Transaction volume in the drug store sector slowed over the past 18 months due to investor trepidation about the proposed merger between the retail giants Walgreens and Rite Aid, according to a new study out from the Boulder Group, a net lease firm in suburban Chicago. And until buyers know all the details of the deal, recently delayed and then approved by the government, they will continue to hedge their bets.