Perrigo Company plc is an Irish–registered manufacturer of private label over-the-counter pharmaceuticals, and while 70% of Perrigo's net sales are from the U.S. healthcare system, Perrigo is legally headquartered in Ireland for tax purposes, which accounts for 0.60% of net sales. In 2013, Perrigo completed the 6th–largest U.S. corporate tax inversion in history when it reregistered its tax status to Ireland to avoid U.S. corporate taxes.Perrigo engages in the acquisition (for repricing), manufacture, and sale of consumer healthcare products, generic prescription drugs, and active pharmaceutical ingredients (APIs), primarily in the United States, from its base in Ireland. On 21 December 2018, Perrigo suffered its biggest one-day share price fall in its history after the Irish Revenue Commissioners issued a tax claim against Perrigo that equated to half of its market value.