Q. I drink tonic water all the time. (Really it is half tonic water and half regular water to help with the cramps I get in my legs.) A friend told me the other day that tonic water has been linked to hearing loss. Is that true?
A. Tonic water contains quinine, which is why it seems to help with leg cramps. Quinine has been known to cause both hearing loss and ringing in the ears.
The dose you are getting is extremely low, however, so it is not clear that this would be a danger. Tonic water can contain no more than 83 mg of quinine per liter in the US. Since you are diluting your tonic water, you aren’t getting very much quinine.
Concerns about quinine toxicity (irregular heart rhythms, blood disorders and severe allergy) led the FDA to forbid its use for preventing leg cramps. When doctors prescribed quinine for this purpose, the dose was 200 to 300 mg a night.