The correct answer is D. It is unlikely that the patient’s friends have been plotting to murder him, and more likely that this false belief is a non-bizarre delusion, and therefore the patient is likely experiencing psychosis. His evasiveness about substance use and injected conjunctiva could be explained by a recent history of cannabis use, and and while it is certainly possible that this is A)Brief Psychotic Disorder, it is less likely. It is less likely B) Schizophrenia because we do not have the timeline nor the amount of symptoms necessary to make the diagnosis. The diagnosis of substance induced psychotic disorder can be made when there is evidence of delusions and/or hallucinations following the use of a substance that can cause those symptoms. Additionally, the episode must not be better explained by another psychotic disorder (symptoms appeared before using the drug, the symptoms last for over a month, or the substance has no documented evidence of causing psychosis in anyone else). It is also important that the symptoms cannot better be explained by a delirium. This patient is oriented and has a linear thought process without evidence of fluctuating mental status, which makes C) delirium less likely.

Publication reference : Volkow ND, et al. Effects of Cannabis Use on Human Behavior, Including Cognition, Motivation, and Psychosis: A Review. JAMA Psychiatry. 2016;73(3):292-297. doi:10.1001/jamapsychiatry.2015.3278
Reference URL: https://archpsyc-jamanetwork-com/article.aspx?doi=10.1001/jamapsychiatry.2015.3278