Walgreens Boots Alliance Inc. agreed to buy Rite Aid Corp. for about $9.4 billion, in a move that would create a drugstore giant as companies across the U.S. health-care industry look for ways to bulk up.

Walgreens agreed to pay $9 a share in cash for Rite Aid, offering a 48% premium to Rite Aid’s closing price Monday.

Rite Aid’s stock rose 43% to $8.67 on Tuesday after The Wall Street Journal reported on the merger talks. Walgreens shares rose 6.4% Tuesday to $95.16.

The deal, which would unite two of the country’s three biggest drugstore owners, would be likely to draw scrutiny from antitrust regulators, who could demand divestitures in exchange for their approval.

It also adds to a blockbuster year for health-care mergers and acquisitions, helping to put 2015 on track to be the busiest year ever for M&A. Including assumed debt, the transaction is valued at $17.2 billion. Rite Aid’s debt totaled $7.4 billion in August.