The deal combines the largest and third-largest U.S. drugstore chains, based on store counts. And it makes one of the world’s largest pharmaceutical buyers even bigger at a time when other key health care players like insurers and drugmakers also are expanding through multi-billion dollar deals.

Walgreens said it will pay $9 for each share of Rite Aid Corp. That’s a 48 percent premium to Rite Aid’s closing price of $6.08 Monday. Shares of both companies jumped Tuesday after The Wall Street Journal first reported the deal.

The companies said the deal is worth $17.2 billion, when debt is included.

Walgreens Boots Alliance Inc. has more than 13,100 stores around the world. Rite Aid, which is based in Camp Hill, Pennsylvania, has more than 4,600 stores in the U.S.

The companies expect the deal to close in the second half of next year, although given that it is combining the No. 1 and No. 3 players in its industry, it could draw close scrutiny from anti-trust regulators.

It comes less than year after Walgreens bought European health and beauty retailer Alliance Boots. Besides its namesake stores, Deerfield, Illinois-based Walgreens also owns Duane Reade stores in the U.S.

A combination with Rite Aid will give Walgreens additional purchasing power in negotiating prices with drug companies, a hot topic given the rapid rise in cost for some prescriptions.

Adding Rite Aid’s stores could also help Walgreens lower price for its customers because its growing volume of prescriptions would put it in a better position in talks with drug providers.

Rite Aid stores will initially keep its name after the deal closes, Walgreens said, but that may change over time.