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Review
. 2022 Sep 29;8(1):78.
doi: 10.1038/s41537-022-00286-0.

Association between formal thought disorder and cannabis use: a systematic review and meta-analysis

Mathilde Argote  1   2   3 , Guillaume Sescousse  4   5   6 , Jérôme Brunelin  4   5   6 , Eric Fakra  4   7 , Mikail Nourredine  5   8   9 , Benjamin Rolland  4   5   6   10
Affiliations
Review

Association between formal thought disorder and cannabis use: a systematic review and meta-analysis

Mathilde Argote et al. Schizophrenia (Heidelb). .

Abstract

Formal thought disorder (FTD) is a multidimensional syndrome mainly occurring along the psychosis continuum. Cannabis use is known to increase symptoms of psychosis, particularly positive symptoms. However, the impact of cannabis use on FTD in individuals presenting symptoms along the psychosis continuum remains unclear. To address this knowledge gap, we conducted a meta-analysis examining the association between cannabis use and FTD in those individuals. We hypothesized that cannabis would worsen FTD. We conducted a systematic search of the PubMed, ScienceDirect, PsycINFO, Web of Science, Embase and Google Scholar databases up to July 2022. The results were collated through a random-effects model using the statistical software R. Reference lists of included studies were searched for additional relevant publications. Nineteen studies were included, totalling 1840 cannabis users and 3351 non-cannabis users. The severity of FTD was found to be higher in cannabis users (SMD = 0.21, 95%CI [0.12-0.29], p = 0.00009). Subgroup analyses revealed that FTD severity was increased among cannabis users, regardless of the disorder severity: healthy individuals (SMD = 0.19, 95%CI [0.05-0.33], p = 0.02); patients with first-episode psychosis (SMD = 0.21, 95%CI [0.01-0.41], p = 0.04); patients with schizophrenia (SMD = 0.25, 95%CI [0.11-0.38], p = 0.005). Between-group differences were not significant. In line with its already known effect on positive symptoms in psychosis, cannabis use appears to be associated with increased FTD severity all along the psychosis continuum. Future research should consider potential confounding variables such as other substance use disorders and explore how FTD dimensions are impacted by cannabis use.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Prisma flow diagram describing the selection process of included publications.
Fig. 2
Fig. 2
Forest plot displaying results of original analysis combining individual studies and subgroup analyses, standardized mean difference (SMD), its confidence interval (CI), and overall prediction interval (PI), plus the weight of each study.
Fig. 3
Fig. 3
Funnel plot investigating publication bias.
See this image and copyright information in PMC

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