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

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Freda Scheffler, Lebogang Phahladira, Hilmar Luckhoff, Stefan du Plessis, Laila Asmal, Sanja Kilian, Marta Di Forti, Robin Murray, Robin Emsley

Original languageEnglish
Article number114022
JournalPsychiatry Research
PublishedAug 2021

Bibliographical note

Funding Information: This study was funded by New Partnership for Africa's Development (NEPAD) grant, through the Department of Science and Technology, Republic of South Africa, the South African Medical Research Council ‘SHARED ROOTS’ Flagship Project Grant no. MRC-RFAIFSP-01-2013 and an unrestricted grant from Lundbeck International. FS is supported by the South African Medical Research Council (SAMRC) Bongani Mayosi National Health Scholarship Program (BM-NHSP).The work reported herein was made possible through funding by the South African Medical Research Council through its Division of Research Capacity Development (SAMRC RCD) under the National Health Scholarship Programme from funding received from the Public Health Enhancement Fund/South African National Department of Health. The content hereof is the sole responsibility of the authors and does not necessarily represent the official views of the SAMRC. The funding sources had no role in the design of the study, nor during its execution, analyses, interpretation of results and drafting of the manuscript. Publisher Copyright: © 2021 Elsevier B.V. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

King's Authors


Cannabis use is associated with an unfavourable course of illness in schizophrenia, although several factors may confound this association. In this longitudinal study, we explored the influence of cannabis use on baseline symptom severity and treatment outcomes in 98 patients with first-episode schizophrenia spectrum disorders treated with a long acting injectable antipsychotic over 24 months. Using mixed models for repeated measures, we compared visit-wise changes in psychopathology, social and occupational functioning and quality of life between recent/current cannabis users (n=45) and non-users (n=53). There were no significant group by time interactions for any of our outcomes, and with the exception of poorer functionality in cannabis users at baseline, no significant differences in these domains at baseline or month 24. Also, remission rates were similar. However, more cannabis users met our operationally defined relapse criteria compared to non-users, and more frequent cannabis use over the course of treatment, as assessed by positive urine toxicology testing, predicted relapse. Our results suggest that cannabis users do not have poorer treatment response than non-users in terms of symptom reduction over the 24 months of treatment. However, dose-related risk of relapse remains with ongoing cannabis use, possibly by directly reducing the threshold for psychotic breakthrough.

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