In the film 6 college buddies decide to decamp to Ireland to partake of the local mushrooms (though quite why they decamp there isn't terribly clear, doing something so blatantly hedonistic is usually a bad idea in horror films). They turn up in a "bad Catholic" children's home to take the mushrooms and proceed to tell each other ghost stories (which again beggars the question "why, wouldn't it kill the safety you need if you're going to trip?"). When they trip in the morning, all hell breaks loose (as per all slasher movies). As is the way in this sort of film there's a (totally expected) twist in the tail.
Other than the really obvious point that "drugs are bad" (which is labored beyond the point of resuscitation in the film) there isn't much to commend "Shrooms." It seems to want to be another "Blair Witch Project," but turns out to be a slightly warmed over version of "Blair Witch 2: Book of Shadows"