Alan Browne wrote,on my timestamp of 13/06/2012 7:03 AM:

Apparently today's tonic water's do not contain the same amount of quinine as
original tonic waters which were part of a strategy to prevent (moderate?
treat?) malaria.

They wouldn't be called "tonic water" if they didn't have the quinine.
And they are still used for that purpose in places where malaria is widespread.