Adolescent Cannabis Use Linked to Earlier Onset and More Hospitalizations in Schizophrenia | Research

The takeaway

In a longitudinal follow-up of Swedish military conscripts, those who developed schizophrenia with a history of adolescent cannabis use had earlier disease onset, more hospital admissions, and more total hospital days than those without cannabis history.

Clinicians treating psychosis and families concerned about adolescent cannabis use

160 schizophrenia patients followed

What the researchers found

Among 160 patients with validated schizophrenia, the 32 with a cannabis history had earlier age at onset, higher number of hospital admissions, and higher total hospital days compared to the 128 without. There was no significant difference in type of onset or clinical symptom profiles between the groups.

Why it matters

This study goes beyond asking whether cannabis causes psychosis to examine whether it makes the disease worse when it does occur. The finding that cannabis-associated schizophrenia involves more hospitalizations suggests a heavier disease burden with significant healthcare costs.

The numbers in context

160 patients with schizophrenia; 32 with cannabis history vs 128 without; cannabis group had earlier onset, more hospital admissions, more total hospital days; no difference in symptom profiles

How the study worked

Longitudinal follow-up of Swedish military conscripts with data on adolescent cannabis use and subsequent schizophrenia incidence. 160 patients with validated schizophrenia diagnoses assessed using the OPCRIT protocol. Compared disease characteristics between 32 with cannabis history and 128 without.

What this study cannot tell us

Only 32 patients with cannabis history limits statistical power. Cannabis use measured at conscription may not capture full use history. Cannot separate the effects of pre-illness cannabis use from continued post-illness use. Male military conscripts may not represent the broader population.

How to read the evidence

Longitudinal design with validated diagnoses, but small cannabis subgroup and male-only conscript sample

When this study was published

2023 study

The bigger picture

If adolescent cannabis use leads to not just higher risk of schizophrenia but also a more severe course, the public health implications extend beyond prevention of onset to the management and cost of treatment for those who develop the disorder.

Questions still open

Does continued cannabis use after diagnosis worsen outcomes further? Would early intervention for cannabis use in psychosis-prone youth improve long-term outcomes? Is the earlier onset due to cannabis accelerating the disease or unmasking it sooner?

Common questions

Does cannabis make schizophrenia worse?

In this study, people who used cannabis as teenagers and later developed schizophrenia had earlier onset and needed more hospitalizations than those without cannabis history. The symptom types were similar, but the disease course was more burdensome.

Did cannabis cause the schizophrenia in these patients?

This study cannot answer that definitively. It focused on whether the course of schizophrenia differed based on cannabis history, finding a heavier disease burden in the cannabis group regardless of causation.

Read the original research

Does a history of cannabis use influence onset and course of schizophrenia?

Acta psychiatrica Scandinavica, 147(6), 614-622

View on PubMed ↗Publisher’s paper ↗

Citation

Allebeck, Peter; Gunnarsson, Tove; Lundin, Andreas; Löfving, Sofia; Dal, Henrik; Zammit, Stanley. (2023). Does a history of cannabis use influence onset and course of schizophrenia?. Acta psychiatrica Scandinavica, 147(6), 614-622. https://doi.org/10.1111/acps.13562