[olva22]

Not original poster, but thinking this was a joke about Tonic water that contains Quinine, a close relative of Chloroquine.

[OJFord]

Wikipedia says chloroquine is 'a quinine' - is the only joke that the amount in tonic water isn't enough to have the desired effect?

That is (historically) why it's there (and called 'tonic') after all, for malaria, which is also mentioned as a use on the chloroquine page.