I took Thiamin quite by chance when a nice person gave me some on the first couple of days of my holiday. I suffer from really bad problems and they worked for me. Having said that, I took 2 per day 200mg and used Soltan After Sun with mossie repellent and have 3 mossie things plugged in the room with the tablets changed every night. I took them after two days of being there and they worked. So take them before you go and keep taking them all the time you are there and do what I did, then maybe you would be ok.