Here's my take on it:
(From my blog, www.kratcreation.blogspot.com):
First of all, I want to make it clear I despise recreational drug use. Why anyone would want to put themselves in a psychotic or senile state is beyond me. That said, my solution to this social problem has always been to let the idiots who must indulge do so at their own determent. Let them also absorb the cost of their stupidity and not force the rest of us to shoulder it. I figure it would be one way to clean out the gene pool.
Shrooms is one of the better indie horror movies I've watched in a long time. Filmed in the backwoods of Ireland, it has the rustic feel of terror. This is something those Evil Dead movies mastered. Anyone who's ever camped in a rural area knows the fear of something moving around your tent at night.
The plot involves a group of college kids who travel to Ireland to experience hallucinogenic mushrooms in the safety of the wild. They are met at the airport by an old hippy who is to be their "guide" through the trip. Although the movie sets us up with a bunch of stereotypes (catholic school girls, jock, stoner), the actors are capable enough to handle the roles. Once at their campsite, after encountering the prerequisite crazy hillbillies, the guide takes their cell phones away, because he doesn't want them freaking out and calling "mommy". We get a lecture on what kind of mushrooms can be ingestible for the "trip" and which ones will kill you on the spot. While gathering the ingredients, one girl ingests one of the wrong kind and things really take off.
Most of the movie is a standard psycho-killer knife-slasher carnival. However, it's also told from the viewpoint of the girl who took the dangerous mushroom. Thus, you never know how much of the plot is her hallucination and how much is real. Coupled with a creepy campfire story their hippy guide has told the them the previous night, her visions become increasingly bizarre.
It has the "twist" ending which so many horror films employ these days. I hat this little convenience. Every since "I see dead people" became a popular phrase, the surprise ending has turned up all over the place. I wish someone would lock this device in a cave for the next 300 years.
Well worth the DVD rental fee, it comes with a director commentary and deleted scenes. It's a scary little movie and you don't need controlled substances to become involved in the plot.

"It's alive!"
Spy Safe House