Medicinal tonic water originally contained only
carbonated water and a large amount of quinine. Most modern tonic waters contain comparatively less quinine, and are often enhanced by citrus flavours. As a result of the lower quinine content, tonic water is less bitter. It is also usually sweetened, often with the addition of
high-fructose corn syrup or sugar. Some manufacturers also produce diet (or "slimline") tonic water, which may contain
sugar substitutes such as
aspartame. Traditional-style tonic water with high amounts of quinine and carbonated water is less common, but may be preferred by those who desire the bitter flavour. In the United States, the US
Food and Drug Administration (FDA) limits the quinine content in tonic water to 83
ppm (83 mg per litre). In Europe, the limit is 100 mg/L, which is 0.25–0.50% of the original strength. The therapeutic dose of quinine is 10 mg/kg every eight hours for effective malaria prevention (2,100 mg daily for a adult). Until about 2010, quinine was often recommended as a relief for leg
cramps, although medical research suggested some care was needed in monitoring doses. Because of quinine's risks, the FDA cautions consumers against using "off-label" quinine drugs to treat leg cramps. ==Use==