We discusses quinine and I decided to do research. Here is what I found:
"... 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. ..."