Snake oil is a term used to describe deceptive marketing, health care fraud, or a scam. Similarly, snake oil salesman is a common label used to describe someone who sells, promotes, or is a general proponent of some valueless or fraudulent cure, remedy, or solution. The term comes from the "snake oil" that used to be sold as a cure-all elixir for many kinds of physiological problems. Many 19th-century United States and 18th-century European entrepreneurs advertised and sold mineral oil as "snake oil liniment", making claims about its efficacy as a panacea. Patent medicines that claimed to be a panacea were extremely common from the 18th century until the 20th, particularly among vendors masking addictive drugs such as cocaine, amphetamine, alcohol, and opium-based concoctions or elixirs, to be sold at medicine shows as medication or products promoting health.

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.