Formal thought disorder (FTD) is a multidimensional syndrome occurring along the psychosis continuum. A meta-analysis of 19 studies including 1840 cannabis users and 3351 non-cannabis users found that cannabis users had higher severity of FTD (standardized mean difference = 0.21). This increase was present regardless of disorder severity: in healthy individuals, patients with first-episode psychosis, and patients with schizophrenia. Between-group differences were not significant. Cannabis use appears to be associated with increased FTD severity all along the psychosis continuum, consistent with its known effect on positive symptoms.
A systematic review of 31 studies involving 2639 participants found that 12 studies reported a significant decrease in craving for alcohol, opioids, cocaine, or tobacco after psychedelic use. However, all but two studies had moderate to high risk of bias due to methodological issues, so the promising anti-craving effects must be interpreted cautiously. The review highlights the need for larger, well-controlled trials to better understand psychedelics' effects on craving, a core symptom of substance use disorders and a predictor of relapse.