You may have heard that malaria tablets are less expensive if you buy them in the country you are travelling to. However, malaria tablets need to to be taken one day to three weeks before you travel. So if you wait until you arrive in a country to obtain antimalarials, you risk exposure to malaria. Besides, if you are not familiar with a country, it may be harder to distinguish genuine and legitimate malaria tablet providers from others who may try to sell faulty, out-of-date or fake medications.
This depends upon which type of malaria tablets you are using.
Malarone (Atovaquone/proguanil) should be started one to two days before your trip and for one week after your return.
Doxycycline should be taken for two days before you travel and for four weeks after your return.
Lariam (Mefloquine) should be taken three weeks before your trip and for another four weeks after you have returned.