On May 1, 2014, "Deadline" reported that Charlize Theron had acquired the film rights to Susannah Cahalan's 2012 memoir "Brain on Fire: My Month of Madness". Dakota Fanning was set to play Cahalan, a young woman who one day wakes up in a hospital with no memory of the events of the previous month. Theron would produce along with Beth Kono and A.J. Dix through her banner Denver and Delilah Productions. On January 22, 2015, Irish filmmaker Gerard Barrett was set to write and direct the adaptation, while Rob Merilees of Foundation Features would produce and finance the film. London-based Mister Smith Entertainment sold the film to international distributors at 2015 Berlin Film Festival. Will Poulter was added to the cast on February 4, 2015, to play Cahalan's boyfriend. On May 26, 2015, Thomas Mann and Jenny Slate were reportedly in talks to join the film, where Mann would play Cahalan's boyfriend, replacing Poulter. On June 26, 2015, it was announced that Dakota Fanning had left the project due to scheduling issues, and Chloë Grace Moretz replaced her for the lead role. On July 7, 2015, it was announced that Broad Green Pictures had come on board to produce and finance the film as well as distribute the film in the United States, while Lindsay Macadam would also produce along with producing partner Merilees. On July 16, 2015, Carrie-Anne Moss and Richard Armitage were cast as Cahalan's parents, Rhona Nack and Tom Cahalan, respectively. On July 20, 2015, Tyler Perry joined the film to play Richard, Cahalan's boss at the "New York Post".