Snake oil

Snake oil is a term used to describe deceptive marketing, health care fraud,
or a scam. Similarly, “snake oil salesman” is a common expression 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 (often mixed with various active and inactive household herbs, spices, drugs, and compounds, but containing no snake-derived substances whatsoever) 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. 

Source: https://en.wikipedia.org/wiki/Snake_oil