There are antimalarial medications, but they can be expensive, have nasty side effects, and don't work in every case. (Also, malaria is becoming resistant to many of these drugs.)

They're OK if you're just traveling or working temporarily in a place where malaria is endemic (check the CDC's recommendations in the link above to find out which one you should take). But they're not so great if you're considering a lifetime of use. For example, long-term use can cause a variety of more serious side effects. Also, many antimalarials can't be taken by, or are more dangerous in, pregnant or nursing women or young children--the very people who need the protection the most.