The FDA requires the use of a U.S. Agent to the Food and Drug Administration for all companies and manufacturers that do not have a presence in the United States. A U.S. Agent to The Food and Drug Administration (FDA) must be a resident of the United States, or have a physical place of business in the United States. A U.S. Agent to the FDA may not use a Post Office address, or answering service, without a physical presence; rather, a U.S. agent to the FDA must answer phone calls, or have employees who are available throughout a business day.