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The specialty drug company AbbVie will spend $63 billion to acquire Allergan, the maker of Botox and other cosmetic treatments.

The two pharmaceutical companies have little in common, save for a desire to reinvigorate growth that has sputtered. Shares of AbbVie are down 16% over the past year and shares of Allergan, with sales growth down over the past three quarters, have fallen 24%.

“This is a transformational transaction for both companies and achieves unique and complementary strategic objectives,” said AbbVie CEO and Chairman Richard Gonzalez in a prepared statement Tuesday. “The combination of AbbVie and Allergan increases our ability to continue to deliver on our mission to patients and shareholders.”

The maker of the global blockbuster immune disorder treatment Humira will pay $120.30 in cash and a portion of AbbVie stock for each Allergan share. That amounts to $188.24 per share, or a 45% premium to Allergan’s closing price Monday.

AbbVie is facing the expiration of patent protection for Humira, which brought in a staggering $20 billion in sales last year.

Industry analysts had been anticipating a move by AbbVie to offset the introduction of generics to an extremely valuable pipeline for the company.

“We are unsurprised by the timing and the target of the deal given (AbbVie’s) Humira patent cliff,” wrote Citi analyst Andrew Baum.

Shares of Allergan Plc, based in Dublin, Ireland, soared 31.2% in premarket trading Tuesday.

AbbVie shareholders will own 83% of the specialty drug company combination after the deal’s completion, while Allergan shareholders will have a 17% stake.

Gonzalez will remain chairman and CEO at AbbVie. Two members of Allergan’s board, including chairman and CEO Brent Saunders, will join AbbVie’s board once the deal closes.

Regulators and Allergan shareholders still have to approve the deal.

Shares of AbbVie Inc., based in North Chicago, Illinois, declined 8% before the market opened.