You've got to be pounding back G&Ts more or less non-stop - or your tonic has to be ridiculously powerful - for it to become a serious problem.
It does seem from the interview and some quick reading that tonic water today uses far less quinine than before. Also I imagine that most companies extract quinine differently today than they did in the old colonial days. Does anyone have an idea of how much more quinine early tonic waters had? It almost seems like the doctors would have thought, "the more quinine you can stomach, the better!" That kind of thinking reminds me of the patent medicines of early America, or the fish oil craze a couple years back. People are always searching for some kind of nostrum!