It depends on WHICH medication, obviously. The standard anti-malarial in WWII was Atabrine, which didn't work very well; a lot of soldiers serving in the tropics developed malaria despite taking Atabrine. I took Paludrine daily for 4 years as a teenager and it apparently did me no harm, but it wasn't totally reliable either. When the Paludrine failed and I developed malaria anyway I was treated with chloroquine, which has been known to have unpleasant side effects in a small portion of the people who take it, but didn't harm me. 

Almost certainly, you didn't take mefloquine.