Tonic water is a carbonated beverage that derives its somewhat bitter taste from the addition of quinine. It is usually flavored with lemon or lime, lots of sugar, and often contains caffeine. Tonic is a frequent mixer in cocktails, most famous for its use in gin and tonic, though vodka with tonic water is also popular. Tonic water may additionally be used with sweet alcohols like vermouth, to produce a balanced taste.

Tonic water was first patented in England in the mid 19th century. In the mid 20th century the company Schweppes, known for their ginger ale, introduced it to the US. It has been popular in both countries since it was first mass-marketed. The popularity owes much to an urban legend regarding quinine.

Quinine became recognized as early back as the 17th century as a relatively safe cure and preventative of malaria. Quinine derives from the bark of the Cinchona, a tree grown in the Andes. It was brought back to Europe, where it was found particularly useful for treating malaria caught during occupation and takeover of islands most known for the illness. The British occupation in India was much aided by quinine, since it allowed the officers to stay well.

The trouble with quinine is that it tastes absolutely wretched. British soldiers tended to take the medication diluted with a great deal of gin, some lemon or lime, and sugar. When tonic water was first produced, people concluded that a few gin and tonics would be good for the health and prevent malaria.

Tonic water, however, contains too little quinine to actually prevent malaria. Actually, chemically produced quinine in much larger doses is now preferred. Quinine therapy does not exactly kill malaria either, but tends to reduce fever and malarial symptoms. Generally malaria needs antibiotics as well to produce full recovery. One would need to drink at least 60 fluid ounces (1.77 liters) of tonic water a day, or the equivalent of ten gin and tonics. In that case, preventing malaria would come with a heavy cost.

Though tonic water lacks enough quinine to reduce symptoms of malaria, it still is called a “tonic” meaning essentially healthful, from its use of quinine. There is no known benefit to consuming tonic water, which has a sugar content equivalent to most sodas. Nevertheless, the name and the drink remain popular.