patent medicine

:  a nonprescription medicinal preparation that is typically protected by a trademark and whose contents are incompletely disclosed; also :  any drug that is a proprietary ◆Patent medicine is often used to refer to a product (such as an elixir, tonic, or liniment) that was marketed as a medicine in the U.S. during the 1800s and early 1900s but was typically of unproven effectiveness and questionable safety.