Mallinckrodt Pharmaceuticals is an Irish–tax registered manufacturer of specialty pharmaceuticals , generic drugs and imaging agents. In 2017 it generated 90% of sales from the U.S. healthcare system. While Mallinckrodt is headquartered in Ireland for tax purposes, its operational headquarters are in the U.S. Mallinckrodt's 2013 tax inversion to Ireland drew controversy when it was shown Acthar, was Medicaid's most expensive drug. Mallinckrodt acquires , manufactures, and distributes products used in diagnostic procedures and in the treatment of pain and related conditions. This includes the acquisition, manufacture, and distribution of specialty pharmaceuticals, active pharmaceutical ingredients, contrast products, and radiopharmaceuticals. The company employed 5,500 and had net sales of $3.2 billion in 2017; of which $2.9 billion was from the U.S. healthcare system.