Patent medicine is the rather misleading term given to different medical compounds sold under a mixture of names and labels, though they were, for the most part, really medicines with trademarks, not patented medicines. In antique times, such medicine was called nostrum remedium, "our remedy" in Latin, thus the name "nostrum," that is also used for such medicines; it is a medicine whose effectiveness is questionable and whose ingredients are typically kept secret. The name patent medicine has become mainly linked with the sale of drug compounds in the nineteenth century under wrap of colorful names and even more colorful claims. The endorsement of patent medicines was one of the first main products of the advertising industry, and many advertising and sales techniques were pioneered by patent medicine promoters. Patent medicine marketing often talked up exotic ingredients, even if their real effects came from more colorless drugs. One excellent group of patent medicines - liniments that supposedly contained snake oil, supposedly a universal panacea - made snake oil salesman a permanent synonym for a charlatan.

The expression patent medicine comes from the early days of the marketing of medical elixirs, when those who found favor with royalty were issued letters patent authorizing the use of the royal support in advertising. The name wedged well after the American Revolution made these endorsements by the crowned heads of Europe outdated. Few if any of the nostrums were really patented; chemical patents came into utilize in the USA in 1925, and in any case attempting to control a drug, medical device, or medical process was considered unprincipled by the standards upheld during the era of patent medicine.

Instead, the compounders of these nostrums used a prehistoric version of branding to differentiate themselves from the crowd of their competitors. Many common names from the era live on in brands such as Luden's cough drops, Lydia E. Pinkham's vegetable complex for women, Fletcher's Castoria, and still Angostura bitters, which were once marketed as a stomach remedy. Several of these medicines, though sold at high prices, were made from quite inexpensive ingredients. Their work was well known within the pharmacy trade, and druggists would trade medicines of almost identical work that they had manufactured themselves. To defend profits, the branded medicine advertisements laid great stress on the brand-names, and urged the public to believe no substitutes.