Common Sense Note
Parents need to know that much swearing (from all ages) and sex talk represents the generally anti-establishment viewpoint of the hero here: an angry, possibly mentally ill teen. Classroom vandalism (apparently committed by the hero under some sort of spell) and profane disrespect of teachers and authority-figure adults is part of the plot, and not exactly frowned upon. There is teen sex (non-explicit), references to pornography, and violent death at the end.
Donnie and his new girlfriend have sex, though nothing is shown. Discussion of sex and (non-clinical) child pornography. A nude woman in a painting briefly glimpsed.
A character fatally shot in the eye (appearing in bloody, ghostly form). Another character fatally run over by an automobile. Fistfights between teens, knife pulled on the hero. Gore is more extreme on the DVD "extras" and the Director's Cut.
"F--k," "s--t," and "bitch" (son says this to his mother).
We never get clinical details info on Donnie's emotional instability -- he may be delusionally schizophrenic, a defiant kid mistreated by The System, or both -- but the film is clearly on his side, as a smart and unappreciated boy. More than it is on the side of the people he scorns and hurts, like an upbeat gym teacher or a gung-ho motivational speaker. Donnie (possibly in a trance state) commits vandalism and sabotage and even murder, though you can argue that he sacrifices himself in the end to undo all that and save others. Donnie's parents, despite all the family and social dysfunction, have a solid and loving relationship.
There is an obscene teen discussion of the sex life of Smurfs (Donnie turns out to be a huge fan). A plug for the Stephen Hawking book A Brief History of Time and a certain national video-store chain.
Drugs / Tobacco /
Teens and adults smoke cigarettes. Donnie is supposed to take prescription pills for his emotional problems.