Cannabis-related psychosis hospitalizations in Portugal increased 29-fold from 2000 to 2015 | Research

The takeaway

In Portuguese public hospitals, hospitalizations with a primary diagnosis of psychotic disorder and secondary diagnosis of cannabis abuse or dependence rose from 20 per year in 2000 to 588 per year in 2015, a 29-fold increase.

Psychiatrists, public health researchers, and drug policy analysts.

29-fold increase in cannabis-related psychosis hospitalizations

What the researchers found

Cannabis-related psychotic disorder hospitalizations rose 29.4 times over 15 years. Among all psychosis hospitalizations, those with a cannabis diagnosis increased from 0.87% in 2000 to 10.60% in 2015. Patients were predominantly male (89.8%) with a mean age of about 31 years.

Why it matters

The dramatic increase occurred during a period of changing cannabis consumption patterns in Portugal, including higher potency products and more frequent use, suggesting a dose-response relationship at the population level.

The numbers in context

Hospitalizations rose from 20 (2000) to 588 (2015). Total: 3,233 hospitalizations. Average cost: about 3,500 euros per episode. 89.8% male. Mean age: 30.66 years. Cannabis coding rose from 0.87% to 10.60% of all psychosis hospitalizations.

How the study worked

Retrospective observational study analyzing all hospitalizations in Portuguese public hospitals from 2000 to 2015. Cases were identified by primary diagnosis of psychotic disorder/schizophrenia with secondary diagnosis of cannabis dependence or abuse (ICD-9 codes).

What this study cannot tell us

Administrative data relies on coding accuracy, and increased awareness of cannabis-psychosis links may have led to more frequent secondary diagnosis coding over time. The study cannot establish causation between cannabis use and psychosis.

How to read the evidence

Moderate: nationwide hospital data over 15 years, though limited by diagnostic coding changes over time.

When this study was published

Published in 2020 in International Journal of Methods in Psychiatric Research.

The bigger picture

While improved diagnostic coding may partly explain the trend, the authors note that changes in cannabis consumption patterns, including more potent products and higher-dose users, likely contributed to the increase.

Questions still open

How much of the increase reflects actual rises in cannabis-related psychosis versus improved diagnostic coding? Has the trend continued after 2015? How does Portugal's decriminalization policy factor into these patterns?

Common questions

Did more people actually get psychosis from cannabis?

The study cannot definitively answer this. The 29-fold increase may partly reflect better recognition and coding of cannabis-related psychosis by clinicians, rather than a pure increase in cases. However, changing cannabis consumption patterns likely also played a role.

Who was most affected?

Nearly 90% were male, with a mean age around 31 years. The gender and age profile is consistent with the known demographics of both heavy cannabis use and first-episode psychosis.

Read the original research

Psychotic disorders hospitalizations associated with cannabis abuse or dependence: A nationwide big data analysis.

International journal of methods in psychiatric research, 29(1), e1813

View on PubMed ↗Publisher’s paper ↗

Citation

Gonçalves-Pinho, Manuel; Bragança, Miguel; Freitas, Alberto. (2020). Psychotic disorders hospitalizations associated with cannabis abuse or dependence: A nationwide big data analysis.. International journal of methods in psychiatric research, 29(1), e1813. https://doi.org/10.1002/mpr.1813