Ireland’s Mallinckrodt the specialty drug makers said Monday that it was acquiring California based Questcor Pharmaceuticals for a stock and cash deal worth more than $5.6 billion.

The transactions will expand the offerings of Mallinckrodt’s specialty pharmaceuticals, including the primary drug from Questcor Acthar, which manages difficult to treat inflammatory and autoimmune conditions.

The terms of the new deal will give stockholders of Questcor $30 per share in cash and 0.897 of a share of Mallinckrodt or $86.08 per share as of the closing price on Friday.

The deal is a premium of more than 33% over the 20-trading day volume average price of Questcor, said Mallinckrodt.

Following the transaction, shareholders at Mallinckrodt will have 50.5% of the new company, while shareholders at Questcor will own the difference.

The boards of both companies have approved the deal unanimously and it is expected to be done by the third quarter of the current year. The deal still needs to receive regulatory and shareholder approval.

Mallinckrodt intends to use cash it has on hand and new debt to finance the new acquisition. Following the closing of the deal Mark Trudeau will run the new company and three new directors will come aboard from Questcor, including the CEO of Questcor Don Bailey.

Questcor will be a separate business unit in Mallinckrodt, which will maintain its headquarters in Dublin.

Acthar, the primary product of Questcor, will complement the portfolio Mallinckrodt has of specialty brands. Acthar generated nearly all of the sales of Questcor. In 2013, sales were $761 million, which was up by 49.5% over 2012.

For the complete year, adjusted profit for Questcor was $337 million, an increase of 61% over the previous full year.

Questcor acquired from Novartis the right last June to develop then commercialize the drug Synacthen in the U.S. Synacthen is used for the treatment of inflamed colons and bowels.

Mallinckrodt in 2013 posted revenues of more than $2.2 billion. The company has over 5,500 employees across more than 70 countries.

This is Mallinckrodt’s second big acquisition this year in the U.S. This past February the company acquired Cadence Pharmaceuticals a biopharmaceutical company based in San Diego for more than $1.3 billion.