A young man presents with psychotic symptoms lasting less than one month. What is the likely diagnosis?

In this scenario, the young man is experiencing psychotic symptoms that have lasted for less than one month. Brief psychotic disorder is characterized by the sudden onset of one or more psychotic symptoms, which may include delusions, hallucinations, disorganized speech, and grossly disorganized or catatonic behavior. The key distinguishing feature of brief psychotic disorder is that these symptoms last for a minimum of a day but less than a month, after which the person returns to full premorbid functioning.

In contrast, schizophrenia requires the presence of symptoms for at least six months, while bipolar disorder involves mood episodes (mania or depression) in addition to potential psychotic symptoms. Delusional disorder, on the other hand, is primarily characterized by the presence of one or more delusions lasting for a month or longer, and typically does not include symptoms that would constitute a full-blown psychotic episode that dominates behavior.

Given that the young man's symptoms are of short duration (less than one month), brief psychotic disorder is the most appropriate diagnosis.