Pfizer Inc, the maker of Viagra and Lipitor, has struck a deal to buy Botox-maker Allergan Plc in a transaction valued at about $160 billion. The complex deal, the biggest ever in the healthcare sector, will allow Pfizer to shift its legal base to Ireland in a so-called “inversion” that would reduce its tax rate.

Pfizer Chief Executive Ian Read will be CEO of the combined company, while Allergan CEO Brent Saunders will be Chief Operating Officer, the companies said on Monday.

In addition to Viagra and its cholesterol drug Lipitor, Pfizer’s major drugs include nerve pain treatment Lyrica and Prevnar, a treatment for pneumonia. Allergan, via its Actavis label, manufactures Teflaro, which is indicated for the treatment of community-acquired bacterial pneumonia (CABP).