(The Wall Street Journal/Twitter)

According to an official statement, the acquisition is worth $66 billion in cash and stock. Based on the current offer, the value of Allergan’s stock could rise to $219 per share when the offer is finalized. Actavis also projects that together, the two companies will have revenue in excess of $23 billion in 2015.

The purchase came after Allergan spent nearly a year fending off takeover attempts by its Canadian rival, Valeant Pharmaceuticals. Allergan would have been Valeant’s seventh acquisition in four years, had Allergan not thwarted the purchase.

The battle for Allergan started in April 2014, when activist investor Bill Ackman and his hedge fund, Pershing Square Capital, began rapidly purchasing the pharmaceutical company’s shares. At the time, Valeant priced Allergan at $47 billion. Ackman, who owns nearly 10 percent of Allergan, urged stockholders and the board to take the offer seriously. In May, Valeant raised its offer to $53 billion. Its final offer came in October, when it promised to acquire the Allergan for $60 billion.

Allergan refused all three proposals and said that Valeant’s “offers [had] been grossly inadequate” and that Valeant “significantly undervalued” the manufacturer’s worth.

The company also expressed concern that after the acquisition, funding from its research and development projects would be cut.

To that end, Allergan began its own publicity campaign in November by posting a petition on the front page of its official website. Targeted at dermatologists, ophthalmologists, optometrists and plastic surgeons, the petition asked medical professionals to sign an open letter.

The letter lauded Allergan’s “industry-leading investments in innovative research and development,” and expressed alarm at Valeant’s “unsolicited proposal to acquire Allergan” and how such a purchase “would greatly decrease funding for R&D.”

News of this morning’s acquisitions quieted worry that changes were imminent in the company’s research and development unit. Mike Ly, a scientist who works for Allergan, said that the company’s Irvine campus would continue in operation and research and development would continue as usual for now.

Apart from Botox, Allergan is known for many cosmetic and over-the-counter medical products. Its facial injection Juvederm is a popular cosmetic filler. The company also manufactures Refresh and Restasis eyedrops, eye-lash lengthener Latisse, and Natrelle, a line of breast implants. Allergan also developed the Lap-Band stomach restricting system, which it sold in late 2013.

None of the companies would officially speak for comment, but J. Michael Pearson, Valeant’s Chairman and C.E.O. said in a statement that the company could not “justify to its own shareholders paying a price of $219 or more per share for Allergan.”

Allergan stock rose more than 5 percent Monday, hitting almost $210 per share. The Actavis purchase of Allergan is expected to be finalized in April 2015.

Reach Staff Reporter Gabe Cortes here.