Cannabis Users with Schizophrenia Respond Similarly to Treatment but Relapse More | Research

The takeaway

Patients with first-episode schizophrenia who used cannabis showed similar symptom improvement over 24 months compared to non-users, but more frequent cannabis use predicted a higher risk of relapse.

Psychiatrists, schizophrenia researchers, harm reduction professionals

Cannabis users had similar treatment response but dose-dependent relapse risk over 24 months

What the researchers found

Among 98 first-episode schizophrenia patients treated with long-acting injectable antipsychotic, cannabis users (n=45) and non-users (n=53) had similar trajectories in symptom reduction and remission rates over 24 months, but more frequent cannabis use (measured by urine testing) predicted relapse.

Why it matters

The nuanced finding that cannabis doesn't impair overall treatment response but does increase relapse risk in a dose-dependent manner suggests that harm reduction approaches focused on reducing use frequency could be clinically valuable.

The numbers in context

98 patients (45 cannabis users, 53 non-users); 24 months of treatment; no significant group x time interactions for symptom trajectories; similar remission rates; more cannabis users met relapse criteria; frequency of positive urine tests predicted relapse.

How the study worked

Longitudinal study of 98 first-episode schizophrenia spectrum patients treated with long-acting injectable antipsychotic over 24 months, comparing cannabis users to non-users using mixed models for repeated measures.

What this study cannot tell us

Moderate sample size; observational design; cannabis users may differ in unmeasured ways; single-site study; urine testing captures recent use but not patterns.

How to read the evidence

Moderate-quality longitudinal study with objective urine testing and standardized treatment, limited by sample size and single-site design.

When this study was published

24-month follow-up of first-episode patients.

The bigger picture

These results suggest cannabis may not fundamentally alter how well antipsychotic treatment works but instead lowers the threshold for psychotic breakthrough, meaning patients who reduce their use may maintain treatment benefits.

Questions still open

Would structured cannabis reduction programs for schizophrenia patients reduce relapse rates while maintaining treatment response? Is there a threshold of cannabis use below which relapse risk normalizes?

Common questions

Does cannabis make schizophrenia treatment less effective?

In this study, cannabis users showed similar symptom improvement over 24 months compared to non-users. However, more frequent cannabis use increased the risk of relapse, suggesting cannabis may lower the threshold for psychotic episodes without fundamentally impairing treatment response.

How was cannabis use measured in this study?

Cannabis use was assessed through urine toxicology testing throughout the 24-month treatment period, providing objective measures of use frequency.

Read the original research

Cannabis use and clinical outcome in people with first-episode schizophrenia spectrum disorders over 24 months of treatment.

Psychiatry research, 302, 114022

View on PubMed ↗Publisher’s paper ↗

Citation

Scheffler, Freda; Phahladira, Lebogang; Luckhoff, Hilmar; du Plessis, Stefan; Asmal, Laila; Kilian, Sanja; Forti, Marta Di; Murray, Robin; Emsley, Robin. (2021). Cannabis use and clinical outcome in people with first-episode schizophrenia spectrum disorders over 24 months of treatment.. Psychiatry research, 302, 114022. https://doi.org/10.1016/j.psychres.2021.114022