Travellers often joke about drinking gin and tonic to prevent malaria, and here is an interesting answer to the question of how many G &Ts would need to be consumed to deliver a preventative dose of quinine?

Short Answer: 67litres per day!!

The Long Answer, for those interested, is according to Meshnick's chapter in "Malaria: Parasite Biology, Pathogenesis and Protection (1998, ed Sherman) that modern tonic water contains 15mg/L quinine, and so has little antimalarial effect. However, Meshnick also mentions that drinking a glass of a decoction of Cinchona bark (made by soaking the bark in brandy or gin for 5 or 6 days) two or three times a day would have provided at least 1-2g quinine per day. Meshnick says that this would have protected against malaria.

Therefore, consuming 67 litres of tonic water would provide 1g quinine. That means a lot of G&T's, and there are definitely easier ways to prevent malaria.