Cannabis Users with Schizophrenia Respond Similarly to Treatment but Relapse More
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Cannabis users had similar treatment response but dose-dependent relapse risk over 24 months
- Evidence Grade:
- Moderate-quality longitudinal study with objective urine testing and standardized treatment, limited by sample size and single-site design.
- Study Age:
- 24-month follow-up of first-episode patients.
- Original Title:
- Cannabis use and clinical outcome in people with first-episode schizophrenia spectrum disorders over 24 months of treatment.
- Published In:
- Psychiatry research, 302, 114022 (2021)
- Authors:
- Scheffler, Freda(3), Phahladira, Lebogang(2), Luckhoff, Hilmar, du Plessis, Stefan, Asmal, Laila, Kilian, Sanja, Forti, Marta Di, Murray, Robin, Emsley, Robin
- Database ID:
- RTHC-03501
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked 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 More on RethinkTHC
- THC-amygdala-anxiety-brain
- anandamide-weed-withdrawal
- cannabinoid-receptors-recovery-time
- cannabis-developing-brain-teenagers
- cant-enjoy-anything-without-weed
- dopamine-recovery-after-quitting-weed
- endocannabinoid-system-explained-simply
- endocannabinoid-system-withdrawal
- nervous-system-weed-withdrawal-fight-flight
- teen-weed-use-under-18-effects-brain
- thc-brain-withdrawal
- thc-prefrontal-cortex-brain-effects
- weed-cortisol-stress-hormones
- weed-memory-loss-recovery
- weed-motivation-amotivational-syndrome
- weed-nervous-system-effects
- weed-reward-system-brain
Cite This Study
https://rethinkthc.com/research/RTHC-03501APA
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
MLA
Scheffler, Freda, et al. "Cannabis use and clinical outcome in people with first-episode schizophrenia spectrum disorders over 24 months of treatment.." Psychiatry research, 2021. https://doi.org/10.1016/j.psychres.2021.114022
RethinkTHC
RethinkTHC Research Database. "Cannabis use and clinical outcome in people with first-episo..." RTHC-03501. Retrieved from https://rethinkthc.com/research/scheffler-2021-cannabis-use-and-clinical
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.