> In the United States, the US Food and Drug Administration (FDA) limits the quinine content in tonic water to 83 ppm[3] (83 mg per liter if calculated by mass), while the daily therapeutic dose of quinine is in the range of 500–1000 mg,[4] and 10 mg/kg every eight hours for effective malaria prevention (2100 mg daily for a 70 kg adult).[5] It is often recommended as a relief for leg cramps, but medical research suggests some care is needed in monitoring doses.[6] Because of quinine's risks, the FDA cautions consumers against using "off-label" quinine drugs to treat leg cramps.[7]

For malaria prevention that's 25 liters of tonic or about about 200 gin and tonics per day.