This one is definitely not great one and has a tag line that you could only get away with in the 70s..
Has the Snakepit been mentioned? I saw that once. Odd it took a long while for One Flew Over the Cuckoo's Nest to be mentioned.
The Persecution and Assassination of Jean-Paul Marat as Performed by the Inmates of the Asylum of Charenton Under the Direction of the Marquis de Sade ? I see it is on You Tube. Don't watch this if you are at all sensitive to extreme philosophy. Marat/Sade (1967) + subtitles - YouTube
Titicut Follies Saw this on TCM a few weeks ago and just rewatched it. This was a1967 documentary, very free form, no narrative, no sense that the sequence of episodes means anything in particular. No hidden cameras, openly filmed. The privacy of the inmates or staff etc is of no issue. Pretty scary. I know changes have been made, but it’s not hard to believe that treatment of the seriously mentally ill is still messy. Some of the actually filmed actions - In one case a weird psychiatrist who can barely speak English interrogates one inmate about masturbation; in another the same psychiatrist administers a force feeding, while a cigarette dangles from his mouth. Brutal looking wardens order inmates to strip and then examine their clothes for something. The Warden? is quite the character, laughing it up as he leads the Follies ( a show put on by and/or for the inmates.) A lawyer or psychiatrist participates in the hearing of patient named Vladimyr who insists that it is the treatment that is making him ill. There was one inmate who was physically deformed. It made me remember that it has been said that plastic surgery would help a great deal of people in difficulty because it is their deformity that lead them to be abused. One particularly vocal inmate who I think calls himself “I, Borgia” defines the Pope as head of the oppression. As noted, a documentary, but worth the watch if you are interested in the real world.
Two of my favorite movies about mental illness are horror movies — “The Babadook” and the original 2008 French version of “Martyrs.”
I’d argue that “Cutter and Bone” is about mental illness and also has a great conspiracy plot to go with it.
The 1955 movie THE COBWEB is worth at least 1 watch. It airs on TCM often enough. That's how I saw it. Same with the already-mentioned 1961 movie SPLENDOR IN THE GRASS. Wasn't the 1989 comedy THE DREAM TEAM about mental illness? The 1983 movie TOUCHED BY LOVE might have been about mental illness; been so long since I've seen it it's hard to remember for sure. I reckon I'll have to look that one up! MY BLOODY VALENTINE (1981) does have important part of the plot regarding a character who goes crazy and starts killing. PHOBIA (1980-Canadian) is a rather odd John Huston-directed movie about a psychiatrist and his patients. Stars Paul Michael Glaser. FUNERAL HOME (1980-Canadian) also has a plot dealing with mental illness. What exactly DID happen to Grandma's mental state when Grandpa ran off with another woman? I wonder . . . I like "Funeral Home" a lot because it's creepy and quite a bit of the movie takes place at night.
Honestly, I didn't expect to love Oliver Stone's "Nixon" but as played by Anthony Hopkins, I really felt for Nixon's character because he reminded me of my own harried father. I thought it was a very sympathetic portrayal (maybe too sympathetic) of a man on the edge of a nervous breakdown.
I was suffering from PTSD at the time that I saw it (original release), so I could really relate to the film. I didn't have it quite as bad as Sandler's character did, but then again, I didn't have it quite as good as he did (Sandler's character was quite wealthy as a result of financial remuneration for his loss {of course, NO amount of money could be enough to recompense for the senseless loss of his family}) either.