Allergan has today agreed to be bought by Actavis for $66 billion, putting an end to a hostile bid by activist investor William Ackman and Valeant Pharmaceuticals.
The offer values Allergan at $219 per share and is $6 billion more than the price Valeant had last offered to pay.
Valeant said in a statement that it could not justify paying such a high price for Allergan, which makes the Botox wrinkle treatment.
Allergan shares rose 6.6% to $211 on Wall Street after the announcement, earning Ackman a payout of more than $2.4 billion on his nearly 10% stake in the company.
Valeant's latest cash-and-stock offer was worth about $54 billion although it had said it would pay up to $200 per share, or about $60 billion.
The deal comes after Allergan spent six months maneuvering against a takeover by Ackman and Valeant.
Allergan's chief executive Officer David Pyott had said shareholders would be hurt because Valeant's cost cutting would stop its growth and he questioned Valeant's accounting.
Actavis CEO Brent Saunders will lead the combined company.
Allergan employs 850 people in Ireland, with the majority of these based in Wesport, Co Mayo. The remainder are in Dublin. Overall the group has a global workforce of about 10,500.
The bid for Allergan has proven one of the most complex and unorthodox in the healthcare sector.