Tonic water is a carbonated soft drink in which quinine

Quinine

Quinine is a natural white crystalline alkaloid having antipyretic , antimalarial, analgesic , anti-inflammatory properties and a bitter taste. It is a stereoisomer of quinidine which, unlike quinine, is an anti-arrhythmic...

 is dissolved. Originally used as a prophylactic against malaria

Malaria

Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...

, tonic water usually now has a significantly lower quinine content and is consumed for its distinctively bitter taste. It is often used in mixed drink

Mixed drink

A mixed drink is a beverage in which two or more ingredients are mixed. Some mixed drinks are alcoholic beverages that contain liquor; others are non-alcoholic.-Types:Some popular types of mixed drinks are:...

s, particularly, in the gin and tonic

Gin and tonic

A gin and tonic is a highball cocktail made with gin and tonic water poured over ice. It is usually garnished with a slice or wedge of lime, or lemon. The amount of gin varies according to taste...

.
The drink gained its name from the medicinal effects of this bitter flavouring. The quinine

Quinine

Quinine is a natural white crystalline alkaloid having antipyretic , antimalarial, analgesic , anti-inflammatory properties and a bitter taste. It is a stereoisomer of quinidine which, unlike quinine, is an anti-arrhythmic...

 was added to the drink as a prophylactic against malaria

Malaria

Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...

, since it was originally intended for consumption in tropical areas of South Asia

South Asia

South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...

 and Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, where that disease is endemic

Endemic (epidemiology)

In epidemiology, an infection is said to be endemic in a population when that infection is maintained in the population without the need for external inputs. For example, chickenpox is endemic in the UK, but malaria is not...

.