Most of the special effects in the film were done practically, with an effort to use as little VFX work as possible. The hallucination scenes' effects in particular were done in-camera. Cronenberg credits his effects specialists, Dan Martin and Derek Liscoumb, and his longtime cinematographer Karim Hussain for being able to pull off convincing visuals with a minimum of CGI.
Brandon Cronenberg says he was inspired to make "Possessor" by two pieces of media. The first is José Delgado's 1970s book "Physical Control of the Mind: Toward a Psychocivilized Society," which "demonstrates how movements can be induced by radio command, hostility may appear or disappear, social hierarchy can be modified, sexual behavior may be changed, and memory, emotions, and the thinking process may be influenced by remote control." The second is a short film, "Please Speak Continuously and Describe Your Experiences as They Come to You," that Cronenberg made in the past.
While developing the movie in pre-production, Brandon Cronenberg found himself gathering inspiration from the films of Dario Argento, particularly "Terror in der Oper (1987)."
In Brandon Cronenberg's home country of Canada, the film that premiered in October 2020 is the uncut version, with a rating of 18A. There were edits made to remove a few minutes of sex and violence in order to achieve an R rating in the United States.
There are two versions of the script for "Possessor." Writer/director Brandon Cronenberg has said there is a possibility of a second movie down the line, one that would encompass the material that didn't make it into this film.