Most brands of tonic water contain quinine, a substance that is used to treat malaria by killing the parasite that causes it. Quinine has been used since the seventeenth century to treat malaria.
For malaria treatment, up to 648 mg of quinine is taken every eight hours for a week. In comparison, tonic water contains a very small amount of quinine. There are around 20 mg of quinine in an 235ml (8 fluid-oz.) glass of tonic water.
Tonic water safety
The amount of quinine in tonic water is usually safe, just like the caffeine in coffee or tea. People who are sensitive or allergic to mefloquine, quinidine, or quinine may experience side effects.
Common side effects
Excessively drinking tonic water may cause diarrhoea, nausea, stomach cramps, vomiting, and restlessness. These side effects may be made worse when tonic water is paired with alcohol.
Anyone who has an allergic reaction after drinking tonic water should stop consuming it. Allergic reactions include rash, itching, hives, difficulty breathing, and swelling of the mouth, face, lips, or tongue.
There is a risk that the quinine in tonic water may interact with blood thinners, antifungals, and heart medications. Always consult your pharmacist or doctor to assess this risk if you take these medications.
This information is not a substitute for medical advice. If you experience unpleasant or dangerous symptoms after consuming tonic water, seek medical help immediately.