Cannabis users with first-episode schizophrenia had earlier psychosis but better starting cognition
Cannabis-using first-episode schizophrenia patients developed psychosis earlier but had better cognitive function at onset (due to higher premorbid IQ), and three-quarters quit cannabis spontaneously over time.
Quick Facts
What This Study Found
Ninety-nine first-episode schizophrenia patients were divided into lifetime cannabis users and never-users. Cannabis users developed psychosis at a younger age, with a strong linear relationship between age of first cannabis use and age of psychosis onset, including prodromal symptoms.
Paradoxically, cannabis users showed better cognitive function at psychosis onset, but this was explained by their higher premorbid IQ, not by a protective effect of cannabis. Social functioning was also better in users.
Remarkably, three-quarters of cannabis users quit spontaneously over the follow-up period. Those who started cannabis later in life quit sooner, and earlier cessation was linked to fewer positive psychotic symptoms and fewer hospital days.
Key Numbers
99 patients, 15-month follow-up. Strong linear relationship between age of first cannabis use and psychosis onset. 75% of cannabis users quit spontaneously. Later cannabis initiation predicted earlier cessation and fewer symptoms.
How They Did This
Prospective cohort study of 99 first-episode schizophrenia patients without other substance abuse. Compared lifetime cannabis users to never-users on premorbid function, cognition, clinical outcomes, and cannabis use trajectory over 15 months.
Why This Research Matters
This study resolved an apparent paradox: cannabis users had earlier psychosis (bad prognosis indicator) but better cognition (good indicator). The explanation was that cannabis brought forward psychosis in people who were otherwise cognitively healthier, meaning early onset was caused by cannabis rather than reflecting intrinsically worse illness.
The Bigger Picture
The finding that most cannabis users with schizophrenia quit on their own challenges the perception that cannabis use is intractable in psychotic patients. The relationship between cannabis cessation and better outcomes provides motivation for treatment programs.
What This Study Doesn't Tell Us
Excluded patients with other substance abuse, limiting generalizability. Cannabis use was self-reported. The linear relationship between cannabis onset and psychosis onset does not prove causation (though the dose-response pattern strengthens the case). 15-month follow-up is relatively short.
Questions This Raises
- ?Would active cannabis cessation intervention improve outcomes further than spontaneous quitting?
- ?Is there a critical cannabis exposure threshold that triggers psychosis?
- ?Can premorbid IQ be used to identify cannabis users at highest psychosis risk?
Trust & Context
- Key Stat:
- 75% of cannabis-using schizophrenia patients quit spontaneously
- Evidence Grade:
- Prospective cohort with careful subgroup analysis. Excludes other substance abuse for cleaner cannabis signal. 15-month follow-up is moderate.
- Study Age:
- Published in 2012. The relationship between cannabis and psychosis onset timing has been confirmed in larger studies since.
- Original Title:
- The effect of cannabis use and cognitive reserve on age at onset and psychosis outcomes in first-episode schizophrenia.
- Published In:
- Schizophrenia bulletin, 38(4), 873-80 (2012)
- Database ID:
- RTHC-00579
Evidence Hierarchy
Enrolls participants and follows them forward in time.
What do these levels mean? →Frequently Asked Questions
Does cannabis cause earlier psychosis?
In this study, there was a strong linear relationship: the younger someone started using cannabis, the younger they developed psychosis. The authors argued cannabis brought forward psychosis in people who would have developed it anyway, rather than causing a fundamentally different illness.
Do people with schizophrenia keep using cannabis?
No. In this study, 75% of cannabis users stopped on their own over the follow-up period. Those who quit sooner had fewer psychotic symptoms and hospitalizations, providing strong motivation for cessation.
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-00579APA
Leeson, Verity C; Harrison, Isobel; Ron, Maria A; Barnes, Thomas R E; Joyce, Eileen M. (2012). The effect of cannabis use and cognitive reserve on age at onset and psychosis outcomes in first-episode schizophrenia.. Schizophrenia bulletin, 38(4), 873-80. https://doi.org/10.1093/schbul/sbq153
MLA
Leeson, Verity C, et al. "The effect of cannabis use and cognitive reserve on age at onset and psychosis outcomes in first-episode schizophrenia.." Schizophrenia bulletin, 2012. https://doi.org/10.1093/schbul/sbq153
RethinkTHC
RethinkTHC Research Database. "The effect of cannabis use and cognitive reserve on age at o..." RTHC-00579. Retrieved from https://rethinkthc.com/research/leeson-2012-the-effect-of-cannabis
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.