Phenomenology of Hallucinations in Endogenous and Substance-Related Exogenous Psychoses

Abstract – Background: Healthcare professionals encounter challenges in discerning endogenous and exogenous, drug-related, psychopathological phenomena. This study aimed to explore qualitative differences between hallucinations in schizophrenia and two forms of substance-related psychosis. These are substance-induced psychosis (SIP), which has an acute onset and is usually transient, and substance-related persistent psychosis (PP). Summary: To explore phenomenological differences, we use an ideal-typical method (which Jaspers borrowed in psychopathology from Weber), together with classic and contemporary phenomenological reflections. After a historical overview of the main issues concerning this topic, we consider the qualitative differences between the different types of hallucinations at the following levels: formal features of the phenomenon, contents, state of consciousness, temporal experience, and position-taking. Key Messages: Our results indicate that while schizophrenic hallucinations typically occur in clear consciousness with variable sensory vividness, SIP hallucinations manifest in an oneiroid state with increased vividness and multisensory integration. In contrast, PP hallucinations occur in a twilight state of consciousness, often presenting as simpler but intrusive phenomena. Furthermore, the discussion includes a brief phenomenological analysis starting from Husserlian conceptions of perception to clarify the basic structural difference underlying the qualitative distinctions previously analysed. By identifying distinctive phenomenological characteristics of hallucinations across these conditions, this study provides clinicians with a conceptual framework for developing more effective diagnostic approaches and therapeutic strategies, particularly in the complex context of substance-induced psychopathologies.