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

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.

Psychotic features, particularly mood incongruence, as a hallmark of severity of bipolar I disorder

“…Again, the direction of this association is elusive. A series of studies have documented associations between high levels of psychoactive cannabis misuse and increased risk of subsequent psychosis in general through a dose–response effect (Robinson et al 2022 ; Hirschtritt et al 2021 ), whereas the reverse direction has also been documented with cannabis use in the context of a psychotic disorder worsening symptomatology and the clinical prognosis of the disorder (Hirschtritt et al 2021 ; Argote et al 2022 ). Further studies are necessary to address the nature and clinical consequences of the comorbidity between cannabis use and MI features.…”

Epigenomic and Other Evidence for Cannabis-Induced Aging Contextualized in a Synthetic Epidemiologic Overview of Cannabinoid-Related Teratogenesis and Cannabinoid-Related Carcinogenesis

“…Cannabis exposure has also been linked with the development of autism-like and ADHD-like syndromes in children [ 117 , 174 ] in spacetime and causal inferential studies [ 175 ] and in epigenomic studies [ 26 , 159 , 176 , 177 ]. An extensive literature and many meta-analyses strongly connect cannabis use and the development of schizophrenia by many mechanisms [ 17 , 178 , 179 , 180 , 181 , 182 , 183 , 184 , 185 , 186 , 187 , 188 , 189 , 190 , 191 , 192 , 193 , 194 , 195 , 196 ].…”

Association between cannabis use and symptom dimensions in schizophrenia spectrum disorders: an individual participant data meta-analysis on 3053 individuals

“…The findings regarding disorganization are not in line with a meta-analysis which found a positive association between cannabis use and Formal Thought Disorder (comprising disorganization) severity. 17 However, this meta-analysis is focused on positive Formal Thought Disorder whereas the current study represents positive and negative dimensions together. A finer analysis would require studying both dimensions separately, using adequate tools.…”

“…Although numerous studies have investigated the influence of cannabis use on positive or negative symptoms, only few studies have investigated the influence of cannabis use on other symptom dimensions in schizophrenia. However, there is evidence that cannabis use is associated with higher severity of disorganization, 17 depression, 18 and excitement. 19 , 20 Besides disorganization, these associations have never been investigated in individuals with schizophrenia.…”