Cannabis-using psychosis patients initially received less severe diagnoses but caught up at second hospitalization | Research

The takeaway

Cannabis users hospitalized for psychosis were initially diagnosed with less severe mental illness at lower rates (20% vs 53%), but by second hospitalization, both groups had similar rates of severe diagnoses around 80%.

Read this if you want to understand how cannabis use affects psychiatric diagnosis and illness trajectory in psychosis.

79-80% of both groups progressed to severe mental illness diagnoses by second admission

What the researchers found

Researchers reviewed records of 318 patients at their first psychiatric hospitalization for psychotic symptoms, comparing 106 cannabis users (33%) to non-drug users. At first admission, the groups differed dramatically in diagnostic severity: only 20.3% of cannabis users received a severe mental illness diagnosis compared to 53.3% of non-users.

However, this gap disappeared by the second hospitalization. Both groups showed conversion rates of 79-80% from non-severe to severe mental illness diagnoses between first and second admissions. Cannabis users had shorter initial hospitalizations, but their five-year rehospitalization rates were not significantly different from non-users.

The high conversion rate in cannabis users raises two possibilities: either severe mental illness was being under-diagnosed at first admission because clinicians attributed symptoms to cannabis use, or cannabis exposure was actively contributing to the development of more severe illness over time.

Why it matters

The finding that cannabis users are initially diagnosed less severely but later receive the same diagnoses has major clinical implications. If clinicians are attributing psychotic symptoms to cannabis use and assigning less severe diagnoses as a result, patients may receive inadequate treatment. Alternatively, if cannabis is driving illness progression, this supports early intervention.

The numbers in context

318 patients total, 106 cannabis users (33.3%). Non-users: 53.3% severe mental illness at first admission. Cannabis users: 20.3% severe mental illness at first admission. Both groups: 79-80% conversion to severe mental illness by second admission. Cannabis users had shorter first hospitalization. 5-year rehospitalization rates were similar.

How the study worked

This was a retrospective chart review cohort study at Geha Mental Health Center, Israel, covering admissions between August 2002 and December 2013. A total of 318 patients were included: 106 cannabis users and 212 non-drug users. Demographics, diagnoses, hospitalization duration, and rehospitalization rates were compared. Diagnostic stability between first and second admissions was assessed.

What this study cannot tell us

Retrospective chart review depends on the quality of medical records. The study was conducted at a single center in Israel. Cannabis use was based on clinical documentation and may be inconsistently recorded. The study could not determine whether cannabis caused illness progression or whether initial diagnoses were simply inaccurate. Only two time points (first and second admission) were analyzed.

How to read the evidence

This is a retrospective cohort study with a reasonable sample size but limitations inherent to chart review methodology.

When this study was published

Published in 2018 with data from 2002-2013.

The bigger picture

This study highlights a critical challenge in psychiatry: disentangling cannabis effects from underlying psychiatric illness at first presentation. The near-identical conversion rates suggest that the initial diagnostic difference may be an artifact of clinical reasoning rather than a true difference in illness severity, raising concerns about systematic under-diagnosis in cannabis-using patients.

Questions still open

Are clinicians systematically under-diagnosing severe mental illness in cannabis-using patients? Does cannabis use accelerate the progression from non-severe to severe psychotic diagnoses? Should first-episode psychosis treatment be more aggressive in cannabis users given the high conversion rate?

Common questions

Do cannabis users get less severe psychiatric diagnoses?

At first hospitalization, yes. Only 20% of cannabis users received a severe mental illness diagnosis versus 53% of non-users. However, by second admission, both groups had converged to approximately 80% severe diagnoses, suggesting initial under-diagnosis rather than truly milder illness.

Does cannabis cause psychosis to get worse over time?

This study cannot definitively answer that question. The high conversion rate (79-80%) from non-severe to severe diagnoses could reflect either under-diagnosis at first admission or actual illness progression. Both mechanisms may be at work.

Read the original research

Differences in demographic and clinical characteristics between cannabis users and non-drug users: A retrospective study of patients at first hospitalization due to psychotic symptoms.

Psychiatry research, 268, 454-459

View on PubMed ↗Publisher’s paper ↗

Citation

Balan Moshe, Livia; Weizman, Abraham; Ben Dor, David H; Konas, Shai; Fischel, Zvi; Aizenberg, Dov; Gothelf, Doron; Valevski, Avi. (2018). Differences in demographic and clinical characteristics between cannabis users and non-drug users: A retrospective study of patients at first hospitalization due to psychotic symptoms.. Psychiatry research, 268, 454-459. https://doi.org/10.1016/j.psychres.2018.07.037