Confirming rumors of the past weekend, US pharmaceutical giant Pfizer has said it will buy drugmaker Allergan for $160 million and move its headquarters to Ireland. The ever faster spinning M&A carousel in the drugs sector has reignited a political debate in the US over the tax-saving maneuver known as inversion.

Allergan is officially domiciled in Ireland but conducts its business from the US state of New Jersey.

Both Democratic party presidential candidates, Hillary Clinton and Bernie Sanders, criticized the plans, and President Barack Obama has previously called inversions “unpatriotic.” While the US Treasury has been taking steps to limit the benefits of such transaction, only Congress is in a position to legislate them out of existence. Due to a divided legislative, no initiatives in this direction are expected, however.

Scheduled to close in the first half of 2016, the merger being structured as an acquisition of Pfizer by Allergan, despite the combined company being called Pfizer and the New York drugmaker’s CEO Ian Read being designated as chief executive. Allergan’s CEO Brent Saunders will become president and chief operating officer.

In its current incarnation, Allergan, whose flagship product is the anti-wrinkle treatment Botox, is the product of a $70.5 billion merger with former competitor Actavis. Following the combination of operations, Actavis changed its name to Allergan.

Under the merger plan at hand, Allergan shareholders would receive 11.3 shares of the combined company for each of their Allergan shares, and Pfizer stockholders would receive one share for each of their Pfizer shares. If all $12 billion of cash is put down, Pfizer said its shareholders would hold about 56% of the new Pfizer with sales of around $64 million. Allergan shareholders would own approximately 44%. The deal includes $8 billion in debt.

Pfizer’s chief financial officer, Frank D'Amelio said management has calculated a combined tax rate of 17-18% for the newly merged company by 2017, compared with about 25% for the current corporation. In a conference call with journalists, Pfizer said also that the combination with Allergan would free up “tens of billions of dollars” parked overseas for other expenditure.

Independent of the transaction, Pfizer said it plans to carry out a $5 billion accelerated share repurchase program in the first half of 2016, leveraging its previously announced repurchase authorization of about $5.4 billion.

The deal that is being called be the biggest-ever merger in the healthcare sector and the largest-even inversion would also create the world's largest drugmaker, toppling Switzerland’s Novartis. At the same time, it would move the US farther away from leadership in the market. For many years the top-ranked pharmaceutical producer, Pfizer has meanwhile been eclipsed by Novartis.

The latest drug company “get together” comes about 18 months after Pfizer’s failed $118 billion bid to acquire AstraZeneca – its first attempt at an inversion. The bid was vehemently rejected by the Anglo-Swedish company’s management and the UK’s political establishment.

Analysts and shareholders of the two merger candidates were less than enthusiastic about the proposed transaction. Analysts expressed disappointment that it would generate lower cost savings than they had forecast and that the process of integrating the two portfolios also would delay a decision by Pfizer to carve out its lower-margin businesses consisting of products facing generic competition. Shares of the two companies fell on the news.

Other observers told news agencies they were disappointed by other aspects of the deal, including the projected cost savings. One said the expected synergies of $2 million over the first three years after closing were only about half the size expected.

Apart from Botox, Allergan also has an Alzheimer’s treatment in the pipeline. Pfizer’s top-selling products include, alongside the erectile dysfunction drug Viagra, the blockbuster cholesterol drug Lipitor and Celebrex/Celebra, an anti-inflammatory drug.