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. This beverage 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 United States. 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 as the 17th century, as a relatively safe cure and preventative treatment for 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 to be particularly useful for treating malaria. The British occupation of India was helped by quinine, since it allowed the British officers to stay healthy.

The trouble with quinine is that it tastes absolutely wretched. British soldiers often would take the medication in a diluted form. The preferred ingredient to dilute the quinine was 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; rather, it 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.