Journal of Psychopharmacology
October 5, 2012
Amir Englund, Paul D. Morrison, Judith Nottage et al.
463 citations
Pre-treatment with 600 mg of cannabidiol (CBD) reduced the likelihood of clinically significant psychotic symptoms and paranoia caused by intravenous delta-9-tetrahydrocannabinol (THC, 1.5 mg) in healthy volunteers. Participants who received CBD before THC had lower scores on the State Social Paranoia Scale and smaller declines in episodic memory compared with those who received placebo before THC. The odds of experiencing a clinically significant increase in positive psychotic symptoms were about 78% lower in the CBD group. These results support the view that cannabis products high in THC and low in CBD pose greater mental health risks.
Frontiers in Behavioral Neuroscience
January 1, 2011
Alessandra Paparelli, Marta Di Forti, Paul D. Morrison et al.
217 citations
Schizophrenia is best understood as a syndrome rather than a single disease, with high heritability and multiple genetic and environmental factors pushing individuals over a threshold into clinical expression. Evidence that certain drugs can induce schizophrenia-like psychosis has been neglected as an environmental factor. Over the past 60 years, understanding the link between drug abuse and psychosis has shaped the modern view that liability to psychosis, including schizophrenia, is distributed continuously through the general population, similar to hypertension and diabetes. This review examines hypotheses arising from the association between common psychotomimetic drugs (LSD, amphetamines, cannabis, phencyclidine) and schizophrenia.
Psychological Medicine
March 18, 2020
Diego Quattrone, Laura Ferraro, Giada Tripoli et al.
89 citations
Daily use of high-potency cannabis is associated with more positive symptoms and fewer negative symptoms in first-episode psychosis patients. Among 901 patients and 1,235 controls across six European countries, those who used high-potency cannabis daily had the highest scores on positive symptoms, while negative symptoms were more common in patients who never used cannabis. Psychotic experiences in controls were linked to current cannabis use but not to lifetime use. Depressive symptoms showed no differences related to cannabis use in either group.
Cannabis and Cannabinoid Research
December 9, 2022
Lucy Chester, Amir Englund, Edward Chesney et al.
20 citations
Inhaling vaporized cannabis containing 10 mg of THC acutely increased blood levels of the endocannabinoid anandamide by 18% and several related noncannabinoid lipids, but adding 10, 20, or 30 mg of CBD did not alter these effects. Over four sessions spaced about two weeks apart, pre-inhalation levels of anandamide and one related compound progressively declined, possibly due to repeated THC exposure or reduced anxiety. The findings suggest that CBD, at the doses tested, does not modulate THC's acute influence on endocannabinoid concentrations, though higher or chronic CBD doses might have an effect.
Psychological Medicine
August 8, 2025
Giulia Trotta, Edoardo Spinazzola, Hannah Degen et al.
4 citations
Childhood trauma, especially emotional and physical abuse, is strongly linked to paranoia, and cannabis use amplifies that effect. In a survey of 4,736 adults, those who experienced childhood trauma reported higher paranoia, and weekly cannabis use—measured in standard THC units—also predicted greater paranoia. Cannabis use partially mediated the link between trauma and paranoia, though trauma itself had a much larger direct effect. The findings suggest that assessing both trauma history and cannabis exposure in standard THC units could improve risk detection and guide interventions for people with childhood trauma.
Frontiers in Psychiatry
July 21, 2026
Kenneth P. Finn, Robin Murray, Elizabeth Stuyt et al.
Cannabis use, especially high-potency products with THC concentrations above 10%, has been linked to rising psychosis cases from 1995 to 2010. Psychosis has multiple causes including genetics, childhood adversity, and drug use. This perspective argues that cannabis-associated violence deserves more attention, presenting high-profile media cases where THC was the only substance involved or cannabis use preceded psychosis and violence. Toxicology often fails to test for THC. The evolving evidence on cannabis, psychosis, and violence should inform medical screening, law enforcement, and policy.
World Journal of Biological Psychiatry
March 22, 2022
D. D’souza, M. Diforti, S. Ganesh et al.
Exposure to cannabis increases the risk for psychoses ranging from transient psychotic states to chronic recurrent psychosis. Greater dose and earlier age of exposure raise the risk. For some psychosis outcomes, evidence supports some causality criteria, but reverse causality and confounders cannot be ruled out. Cannabis is neither necessary nor sufficient to cause psychosis; it is likely one of multiple causal components. In those with established psychosis, cannabis negatively affects the illness course and expression. Emerging evidence suggests alterations in the endocannabinoid system in psychotic disorders. Delaying or eliminating cannabis exposure could potentially reduce psychosis rates, especially in high-risk individuals.
Translational Psychiatry
August 10, 2021
D. Quattrone, U. Reininghaus, A. Richards et al.
Genetic risk for schizophrenia and cannabis use each contribute to specific symptom patterns across psychotic disorders, not just diagnostic categories. Among 617 first-episode psychosis patients, higher schizophrenia polygenic risk scores were linked to more severe negative and positive symptoms, regardless of diagnosis. In 979 controls, the same genetic risk was associated with all dimensions of psychotic experiences. Daily or current cannabis use was tied to more positive symptoms in both patients and controls, beyond the effect of genetic risk. The findings support a dimensional view of psychosis, where genetic liability relates to symptom severity and cannabis use specifically increases positive symptoms.
Schizophrenia Bulletin
November 1, 2008
Cécile Henquet, Marta Di Forti, Paul D. Morrison et al.
Cannabis use is considered a contributory cause of schizophrenia and psychotic illness, but only a small proportion of users develop psychosis. The amount, duration, and strength of cannabis consumption, as well as age at first exposure, partly explain this. Genetic factors likely play a role in both short- and long-term effects on psychosis. This review discusses studies using genetic, epidemiological, experimental, and observational techniques to investigate gene-environment correlation and interaction within the cannabis-psychosis association. Evidence suggests that mechanisms of gene-environment interaction underlie the link, with multiple genetic variations and other environmental factors (e.g., stress) interacting with cannabis to increase psychosis risk. Further research on higher-order interactions is needed.