Current methods for measuring cannabis use in psychosis patients are inadequate | Research

The takeaway

Self-report questionnaires used to assess cannabis use in psychosis patients were designed for other populations and may be inaccurate due to psychotic symptoms, cognitive deficits, and desire to conceal use.

People interested in the cannabis-psychosis relationship and how cannabis use is measured in clinical settings.

Three factors compromise self-report accuracy in psychosis

What the researchers found

Cannabis assessment tools used in psychosis research were originally developed for healthy individuals or people with cannabis use disorder. In psychosis patients, the accuracy of self-report may be compromised by symptoms, cognitive impairment, and motivated concealment. Urinary THC screening is sometimes used in acute episodes but not routinely. Quantitative blood/urine cannabinoid measurement could provide more reliable data but is rarely used.

Why it matters

Accurate cannabis use measurement is critical for managing psychosis, since use is linked to symptom worsening, poor treatment adherence, and relapse. If clinicians and researchers are relying on flawed measurement tools, they may be underestimating the problem.

The numbers in context

Cannabis use is common in people with psychotic disorders. Self-report accuracy may be impaired by three factors: psychotic symptoms, cognitive deficits, and desire to conceal use from clinicians.

How the study worked

Narrative review examining current approaches to assessing cannabis use in people with psychotic disorders, comparing self-report tools with biological measures and discussing limitations specific to this population.

What this study cannot tell us

Narrative review without systematic methodology. Does not quantify the degree of measurement error. Biological measures have their own limitations (detecting use window, cost, invasiveness).

How to read the evidence

Narrative review synthesizing clinical observations. Does not present new data or use systematic methodology, but raises important methodological concerns.

When this study was published

Published in 2024 in Cannabis and Cannabinoid Research.

The bigger picture

The relationship between cannabis and psychosis is one of the most important questions in psychiatric research. But if the measurement of cannabis use in this population is fundamentally flawed, the entire evidence base may be biased, potentially underestimating the true impact of use on outcomes.

Questions still open

Would routine quantitative cannabinoid testing in psychosis patients improve clinical outcomes? How large is the gap between self-reported and biologically verified cannabis use in this population? Could passive monitoring approaches supplement self-report?

Common questions

Why is it hard to measure cannabis use in psychosis patients?

Three factors make self-report unreliable: psychotic symptoms can impair accurate recall, cognitive deficits common in psychosis affect questionnaire performance, and patients may hide use when clinicians have advised against it.

What would be a better way to measure cannabis use?

The authors suggest quantitative measurement of cannabinoid levels in blood or urine would provide more accurate data than asking patients or using questionnaires, though this approach is rarely used in clinical practice or research.

Read the original research

Assessing Cannabis Use in People with Psychosis.

Cannabis and cannabinoid research, 9(1), 49-58

View on PubMed ↗Publisher’s paper ↗

Citation

Chesney, Edward; Lawn, Will; McGuire, Philip. (2024). Assessing Cannabis Use in People with Psychosis.. Cannabis and cannabinoid research, 9(1), 49-58. https://doi.org/10.1089/can.2023.0032