name of a movie about soldiers that are given pills?

what i remember is that they were in a desert in a war, the soldiers
were given pills (some of the soldierdidnt take them) and that there
are scenes when the soldiers get letters and videos from their loved
ones and one of the videos recieved by a soldier was his
wife/girlfriend having $EX with another man (POSSIBLE SPOILER) i think
in the end of the movie the soldiers that took the pills that were
gaven to them died while the others survived

it was a really good movie but i was sleepy while watching it can some
one please help me find the movie ive been looking for it forever with
no results :( some one please help me