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Characterizing psychosis-relevant phenomena and cognitive function in a unique population with isolated, chronic and very heavy cannabis exposure

Published online by Cambridge University Press:  16 October 2019

Deepak Cyril D'Souza*
Schizophrenia and Neuropharmacology Research Group, VA Connecticut Healthcare System, West Haven, CT, USA Abraham Ribicoff Research Facilities, Connecticut Mental Health Center, New Haven, CT, USA Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
Suhas Ganesh
Schizophrenia and Neuropharmacology Research Group, VA Connecticut Healthcare System, West Haven, CT, USA Abraham Ribicoff Research Facilities, Connecticut Mental Health Center, New Haven, CT, USA Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
Jose Cortes-Briones
Schizophrenia and Neuropharmacology Research Group, VA Connecticut Healthcare System, West Haven, CT, USA Abraham Ribicoff Research Facilities, Connecticut Mental Health Center, New Haven, CT, USA Department of Psychiatry, Yale University School of Medicine, New Haven, CT, USA
Michael H. Campbell
Faculty of Medical Sciences, University of the West Indies, Kingston, Jamaica
Maisha K. Emmanuel
Faculty of Medical Sciences, University of the West Indies, Kingston, Jamaica
Author for correspondence: Deepak Cyril D'Souza, E-mail:



The literature on psychosis-relevant outcomes in cannabis users does not adequately address the confounding effects of other substance use/misuse and psychiatric disorders.


We studied a unique population for whom cannabis use is central and necessary to their way of life. They are forbidden from using other substances, including tobacco and alcohol. Their use of cannabis is heavy, chronic, and begins early. The cases were compared with matched controls who did not use cannabis, alcohol, or drugs. The controls were from the same location and shared similar beliefs and lifestyle, except for cannabis use. Attenuated psychosis-relevant phenomena were assessed with the Schizotypal Personality Questionnaire (SPQ) and cognitive functioning with a culture-neutral computerized cognitive battery.


Fifteen cases and 12 matched controls were studied. The cases averaged >30 000 lifetime cannabis exposures. Relative to controls, the cases had significantly higher mean (s.d.) SPQ scores 24 (14.32) v. 13 (8.92), p = 0.031; and poorer cognitive performance, reflected by a lower mean (s.d.) composite cognitive score −0.23 (0.32) v. +0.28 (0.52), p = 0.03. Moderate to large effect sizes were noted for differences in tests of attention, psychomotor speed, working memory, cognitive flexibility, visuo-spatial processing, and verbal memory. A subsample of cases had higher SPQ scores and worse cognitive performance than their siblings not using cannabis.


Heavy, chronic, and early cannabis use that is not confounded by other drug use is associated with psychosis-relevant phenomena and cognitive deficits. The findings are relevant to the evolving attitudes and laws about cannabis.

Original Articles
Copyright © Cambridge University Press 2019

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