Tonic water (or Indian tonic water) is a carbonated soft drink in which quinine is dissolved. Originally used as a prophylactic against malaria, tonic water usually now has a significantly lower quinine content and is consumed for its distinctively bitter taste. It is often used in mixed drinks, particularly the gin and tonic.
The drink has garnered its name from the medicinal effects of this bitter flavouring. The quinine was added to the drink as a prophylactic against malaria, since it was originally intended for consumption in tropical areas of South Asia and Africa, where that disease is endemic. The mixed drink gin and tonic originated in British colonial India when the British population would mix their medicinal quinine tonic with gin to make it more palatable.
Since 2005 there has been an increase in premium tonic water in the market place, there has also been a greater emphasis on using real quinine as opposed to quinine flavouring. These premium mixers typically cost twice or three times as much as their more generic contemporaries and are seen as another way of upselling a drink. 
Medicinal tonic water originally contained only carbonated water and a large amount of quinine. However, most tonic water today contains a less significant amount of quinine, and is thus used mostly for its flavour. As a consequence, it is less bitter, and is also usually sweetened, usually with corn syrup or sugar. Some manufacturers also produce diet tonic water, which may contain artificial sweeteners. Traditional-style tonic water with little more than quinine and carbonated water is less common but may be preferred by those who desire the bitter taste.
In the United States, the Food and Drug Administration limits the quinine content in tonic water to 83 ppm (83 mg per litre if calculated by mass), which is 0.25% to 0.50% of the concentration used in therapeutic tonic. Still, it is often recommended as a relief for cramps. Dr. Jim Mitterando states that "Quinine is one of the few treatments shown to help reduce nocturnal cramps. Quinine is found in low concentrations in tonic water (one-tenth of prescription dose). Drinking 8 to 16 ounces (a quarter to a half litre) at night can be a simple remedy." However, because of quinine's risks, the United States Food and Drug Administration has declared that nonprescription sources, such as tonic water, should not be used to prevent or treat leg cramps.
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