Mallinckrodt Pharmaceuticals is an American-Irish domiciled manufacturer of specialty pharmaceuticals (namely, adrenocorticotropic hormone), generic drugs and imaging agents. In 2017 it generated 90% of its 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.