The deal, while not yet approved by each company's board, is expected to be announced before the open of trading tomorrow, barring a last minute setback. An exact price and specific composition of the deal's stock and cash components was not shared by sources.
Allergan's decision to sell to Actavis comes after a long battle to avoid the clutches of Valeant, which teamed with the hedge fund Pershing Square in making an unsolicited bid for Allergan last spring.
Actavis has been acquiring companies at a breakneck pace. The Allergan deal, which will represent it's biggest purchase yet by far, follows closely on the heels of its acquisition of Forest Labs.