Which condition is classified as a functional behavioral disorder?

Schizophrenia is classified as a functional behavioral disorder because it primarily affects how a person thinks, feels, and behaves, as opposed to being a direct result of identifiable physical changes or damage to the brain, such as those that occur in conditions like Alzheimer's disease or head trauma. Functional behavioral disorders, like schizophrenia, arise from complex interactions between genetic, environmental, and neurobiological factors and often manifest as significant disruptions in a person's ability to function effectively in everyday life.

In contrast, other conditions listed, such as Alzheimer’s disease, are primarily considered neurodegenerative disorders where there are observable physical changes in the brain structure and function. Head trauma involves structural damage to the brain due to an injury, leading to cognitive and behavioral changes. Drug addiction, while it can lead to significant behavioral changes, is often categorized as a substance use disorder rather than a functional behavioral disorder. Hence, schizophrenia fits the criteria for a functional behavioral disorder due to its nature of primarily affecting mental functioning without a direct physical causative factor.