We are particularly concerned about the growing use of cannabis, and the associated perception that it is a recreational drug with little risk of harm, among young adults. In terms of neurodevelopment, late adolescence and early adulthood is a particularly vulnerable time, as the brain is undergoing extensive changes, including the development of higher cognitive functioning and increases in connectivity between various regions of the brain.
Recent studies have indicated that cannabis use in adolescents and young adults may be associated with an increased risk of psychosis. While the etiology of psychotic disorders is not well understood and is clearly influenced by multiple genetic and environmental factors, there has been growing evidence supporting the role that cannabis use as a potentially preventable environmental risk factor for psychosis.
In a recent study, Abigail Wright, PhD and her colleagues at the MGH Depression Clinical Research Program and the MGH Resilience and Prevention Program examined the association between recent cannabis use and psychotic experiences. A cohort of 1034 U.S. college students completed questionnaires assessing cannabis use during the past week. Delusional ideation was measured using the Peters Delusions Inventory, and hallucinations were identified using the Launay-Slade Hallucination Scale-Extended. Depressive symptoms were measured using the Beck Depression Inventory. The mean age of the participants was 19.5 years (SD = 1.3, range 18–28), and 71% of the sample was female.
Individuals who used cannabis in the last week reported a significantly higher number of hallucinatory experiences than those who reported no cannabis use. This finding remained significant after controlling for gender and depressive symptoms. Similarly, those who used cannabis in the last week reported significantly more delusional experiences than non-users. This association remained significant after controlling for gender, but not after controlling for depression.
Wright and colleagues also observed a dose dependent-relationship between cannabis use and psychotic experiences, such that students who reported more frequent cannabis use reported more hallucinations and delusional ideation. However, even individuals who used cannabis once per week, compared to those who used no cannabis, were more likely to report hallucinations. Also of importance is the finding that more frequent cannabis use was associated with more distressing delusional ideas that were held with greater conviction.
Clinical Implications
Individuals reporting higher rates of weekly cannabis use were more likely to report hallucinatory experiences and delusional ideation. The relationship between cannabis use and hallucinations was independent of gender and depressive symptoms, suggesting that this relationship was not related to the effect of cannabis on mood. While this study indicates that cannabis use is directly linked to hallucinations, longitudinal research is needed to better understand the more complex relationships between cannabis use, delusional ideation, and depression.
Taken together with the findings of previous studies, these findings add to the evidence that cannabis use contributes to the emergence of psychotic symptoms that may ultimately lead to the emergence of clinical psychosis, particularly in those users who have additional risk factors for psychosis, including having a first-degree relative with schizophrenia or bipolar disorder, a history of early traumatic experiences, or younger age.
Also concerning is the finding that those who reported more frequent cannabis use had more distressing delusional ideas that were held with more conviction. Prior research indicates that psychotic experiences that are more severe (e.g., distressing and persistent) are associated with an approximately 10-fold increased risk of psychotic illness.
These findings have important clinical implications for college-age students. While complete abstinence from using cannabis may be an effective strategy for reducing psychotic experiences and may reduce their risk for psychotic illness, students may also benefit from reducing the frequency of cannabis use as those who used cannabis more frequently were more likely to experience psychotic symptoms.
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Abigail Wright, PhD
Abigail Wright, PhD is a Postdoctoral Fellow at the Center of Excellence (COE) for Psychosocial and Systemic Research at Massachusetts General Hospital. Her research focuses on understanding difficulties in functioning in schizophrenia with a particular focus on metacognition, and she is using Ecological Momentary Assessment as a method to assess temporal and proximal associations between metacognition, hallucinations, and functioning.
