A patent medicine is a non-prescription medicine or medicinal preparation that is typically protected and advertised by a trademark and trade name, and claimed to be effective against minor disorders and symptoms, as opposed to a prescription drug that could be obtained only through a pharmacist, usually with a doctor's prescription, and whose composition was openly disclosed. Many over-the-counter medicines were once ethical drugs obtainable only by prescription, and thus are not patent medicines.

Quackery, often synonymous with health fraud, is the promotion of fraudulent or ignorant medical practices. A quack is a "fraudulent or ignorant pretender to medical skill" or "a person who pretends, professionally or publicly, to have skill, knowledge, qualification or credentials they do not possess; a charlatan or snake oil salesman". The term quack is a clipped form of the archaic term quacksalver, from Dutch: kwakzalver a "hawker of salve". In the Middle Ages the term quack meant "shouting". The quacksalvers sold their wares at markets by shouting to gain attention.