In this movie or TV show, I don’t remember which it was, there was a group of soldiers who were told that aliens were attempting to take over a moon that has a resource in it that they need to mine to keep their economy running. All the soldiers are told they need a special vaccine infused into their veins to keep them immune to the aliens diseases. One of the soldiers finds out that the vaccine is just a brainwashing fluid that manipulates their brains and the enemy aliens are really just soldiers from another group/country/etc, but the infusions are messing with their brains so they see aliens instead of people. the enemy group is also being brainwashed, at the end I think the soldier that figures it out is murdered by an enemy who then takes an infusion of the vaccine.
I’m pretty sure this was an episode of Star Trek: Voyager. Epiosode 4, “Nemesis”. It doesn’t match your description 100%, but it’s close.
It might be an “Outer Limits” episode. One of the new, in-color, not-very-good episodes.
Specifically, episode 65, “Hearts and Minds”. (http://www.tvtome.com/OuterLimits/guide.html)
It also sounds somewhat similar to a story where soldiers were sent in to neutralize an alien creature; only to discover that the creature was a genetically engineered bioweapon, they were expendable fodder for the creature to hone it’s skills on, and that they were the second or third group to be sent to their deaths.
Sheesh. Have we discovered yet another overused plot device, or what?
For some reason a Sci-Fi flick, Legion, seems to come to my mind as well…
It was the outer limits. I’m going to have to start TiVoing that show.
They just had a big Outer Limits marathon today. I think they played that episode too.
I set my TiVo up but only got the last 4 episodes of that 8-4 marathon. The night visions marathons are great too.