The film stars John Glover, David Mazouz, and Lou Diamond Phillips as three people whose stories ultimately lead them - and friends - to become patients of a sanitarium.
The film is divided into three short stories framed by Dr. Henry Stenson, a psychologist who is treating three patients with unique disorders. Each one is preceded and succeeded by Stenson giving a monologue about his interpretation, except for the last patient, whom he interviews directly. The second patient's story is additionally framed by a psychology student about to write a thesis by reading the patient's file.
Gustav, an aged, disheveled doll artist, works for his old friend, Sam, who helps showcase his creations. He is assisted by the young Mateo, whom he is unaware has been drugging his alcohol with a psychoactive drug which soon drives Gustav into believing that his creations can talk. He is especially obsessed with a female doll whom he named Madeline, who talks him into killing Sam, his assistant, and also Mateo's lover, Isabelle. After Mateo discloses what he had done, Gustav commits suicide, but not before saying that Mateo can now own his creations. The segment is closed with the deranged Mateo opening a box containing Gustav's creations, as Stenson wonders which one is controlling which.
A young boy, Steven, who has catatonic schizophrenia, lives with his abusive father, who forces him to do household chores while he goes to a stripper club everyday. Steven feels stalked by a man clad in black with a black fedora. One day, while having his attention at a friend's pornographic magazine, the man stops him from leaving, revealing his monstrous face, but he suddenly disappears when Steven's teacher, the kind Ms. Lorne arrives and holds Steven responsible for the magazine. Suspecting that his father is abusive after seeing him rudely fetching Steven home while refusing to explain his neck bruise (actually caused by the monstrous man), she trails them. Before Steven is abused, the man manifests and stuffs him into a burlap sack before killing Steven's father. He also kills Ms. Lorne when she comes in, leaving Steven unresponsive by the time the police arrive. Dr. Stenson narrates the events afterward: Steven was transferred to the sanitarium where he remains a catatonic and hallucinating of the monstrous man well into his adulthood, yet he sometimes can see him smiling while looking at the sky.
Presented in an anachronistic order, the segment tells the story of a college professor called James Silo, who is also an avid conspiracy theorist of the 2012 doomsday event. He believes that on 21 December 2012, the planet Nibiru would collide with the Earth and to protect himself and his family, he built a bunker underground, containing a small bedroom and working room, hydroponic culture to sustain food, and a heater. Throughout the segment, it became apparent that James' obsession had distanced himself from reality; his students began to leave his class until no one was left, dismissing him from his university. He ignored his wife, Allison, and sons Caleb and Kyle and spent his savings to build the bunker. Eventually, Allison decided to call the staff from the sanitarium to confine James, yet he managed to escape and began to live in the bunker for over 640 days, believing that he is the last man left and that his family are dead. What James does not learn until the end, however, is that he is the one who killed them after escaping from the sanitarium. In grief, James swallows a pill and opens the bunker to find Allison framed by a white light. She catches him when he falls, caresses him, and says that everything is alright. The segment is closed with the scene before James escaped from the sanitarium. While being interviewed by Dr. Stenson, he states his belief that everything is an illusion and that "they" are laughing at him.
A mid-credits scene shows Stenson discovering James having escaped the sanitarium and left his doomsday timer under the pillow, followed by the first scene of the segment: James waking up to his 640th day in the bunker.Malcolm McDowell as Dr. Stenson
John Glover as Gustav
Robert Englund as Sam
Walter Perez as Mateo
Mayra Leal as Isabelle
David Mazouz as Steven
Lacey Chabert as Ms. Lorne
Chris Mulkey as Father
Brant Bumpers as Creature
Mark Cantu as Police Officer
Lou Diamond Phillips as James Silo
Nova Aragon as Allison Silo
Joseph Rivera as Caleb Silo
Ryder Maldonado as Kyle Silo
Dianah McGreehan as Dr. Williams
Venda D'Abato as Reflection
Valderrama began developing Sanitarium around 2011 and wrote the segments Figuratively Speaking and Up To the Last Man with his writing partner C. M. Bratton. He approached Ramirez and Ortiz with the intention of each of the three directors directing one of the film's stories. Ortiz like the film's concept, as it reminded him of the 1973 film Tales That Witness Madness and the 1980s horror series Tales from the Crypt. Filming for all three segments was done in Texas and each segment was completed in five days. St. Anthony Catholic High School and the area of Monte Vista in San Antonio was used for the second sequence.
Valderrama experienced some difficulty while shooting his segment Up to the Last Man, as the filming location was "the second story of a warehouse in between a highway and a train station in July, with no air conditioning." For the segment Valderrama also researched preppers, as he wanted the actions of James Silo to seem realistic. Ramirez also performed research for the segment Figuratively Speaking as well as drawing on personal experience with being an artist.
Critical reception for Sanitarium has been mixed. The movie received praise from Ain't It Cool News, who wrote that the anthology was "a pretty good one" but expressed some frustration that the dialogue from the mental health physicians was not entirely accurate to how they spoke to patients in real life but also noted that this was a common problem in cinema. Starburst gave the film 7 out of 10 stars, remarking that the film wasn't perfect but that it "does make the most of what it has". In contrast, the San Antonio Current criticized the film as "not very interesting" and remarked that "Wrapping up each segment with a thought-provoking morale would have served the film better. Instead, Sanitarium goes for the cliché and easy way out". Shock Till You Drop panned Sanitarium, praising its production values while opining that it was "too bad such a production went into such bad stories."