Pfizer Inc. on Monday said it would buy Botox maker Allergan Plc in a record-breaking deal worth $160 billion, designed to cut the company's US tax bill by moving its headquarters to Ireland.
The merger, which will create the world's largest drugmaker, will delay the Lipitor and Viagra maker's decision on whether to split by two years to late 2018, Pfizer said.
Investors had been hoping Pfizer would sell off its low-margin generics by 2017 while holding onto its faster-growing branded prescription drugs, a move that will be delayed by the time required to integrate Allergan.
Pfizer Chief Executive Officer Ian Read will hold that position at the combined entity, while Allergan CEO Brent Saunders will be president and chief operating officer.
The deal values Allergan's shares at $363.63 each, about 16 percent more than their closing price of $312.46 on Friday.
Allergan shareholders would receive 11.3 shares in the combined company for each of their shares.
Pfizer stockholders can get cash or one share of the combined company for each of their shares, but the aggregate amount of cash must range from $6 billion to $12 billion.
While the deal is structured as Allergan buying Pfizer, Pfizer would retain control of the company.
The tax aspect of the deal has been seen as critical. The US corporate tax rate of 35 percent is among the world's highest, while Ireland's is just 12.5 percent.
Upon the closing of the transaction in the second half of 2016, the companies said the combined company would maintain Allergan's Irish legal domicile.
Plans call for four current directors of Allergan, including Saunders and Executive Chairman Paul Bisaro, to join Pfizer's 11-member board, the companies said in a joint release.
The US Treasury, concerned about losing tax revenue, has been taking steps to clamp down on tax inversion deals, but experts have said these moves will do little to prevent Pfizer from shifting its domicile.
Reports that the companies were in talks emerged a month ago. Since then, speculation had centered on the terms, the domicile issue and the roles for Read, known for his focus on research and development, and consummate dealmaker Saunders.
The companies' combined medicine chest would put Pfizer staples such as impotence treatment Viagra, cholesterol fighter Lipitor and nerve pain treatment Lyrica alongside Allergan's Botox wrinkle treatment, Alzheimer's drug Namenda and dry-eye medication Restasis.
Allergan's shares were down 1.2 percent in premarket trading, while Pfizer's fell 2.5 percent.
At Friday's close, Allergan shares had risen 8.8 percent since reports of the deal talks emerged on Oct. 28. Pfizer's shares had fallen 9.2 percent.
The businesses of Pfizer and Allergan will be combined under Allergan Plc, which will be renamed Pfizer Plc.