I have been using Demal 200 to prevent malaria while living in Papua New Guinea. I have taken it for two years and have not had malaria in that time, so it looks like it is working to keep malaria away. I have had malaria in the past when I wasn’t taking any prophylaxis, so I do know that I can contract it, but I haven’t had it while using Demal so for me, it seems to be effective in preventing malaria. I don’t know whether it works for everyone though, so take proper precautions.