Cannabis and suicide risk remain unclear in high-risk groups

Substance use and suicidality are prevalent among individuals at ultra-high-risk (UHR) of psychosis, yet their relationship remains unclear. This systematic review synthesises evidence on the relationship between substance use and suicidality-comprising suicidal ideation, self-harm, suicide attempts, and suicide deaths-in the UHR population. A pre-registered systematic review (PROSPERO: CRD42024614852) was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Systematic searches of Embase, Medline, PsycINFO, and Web of Science identified studies examining substance use and suicidality in individuals at UHR. Two reviewers independently extracted data and assessed quality using the Mixed Methods Appraisal Tool. Findings were narratively synthesised. Twelve studies (13 papers; n = 2198) met inclusion criteria. Of 40 analyses, only 13 reported significant associations between substance use and suicidality, most of which were derived from a single study. Tobacco use showed the most consistent preliminary associations with suicidal ideation and self-harm. Alcohol and cannabis were linked to ideation and self-harm in some analyses, and cocaine to ideation only, particularly when continuous measures were used. In contrast, composite substance use variables were largely unrelated to suicide outcomes. Methodological quality varied, with major limitations including reliance on cross-sectional data and the use of dichotomous substance use outcomes. At present, there is insufficient high-quality evidence to establish a reliable association between substance use and suicidality in individuals at UHR for psychosis. Rigorous longitudinal studies using validated, substance-specific measures are needed to better understand these relationships and inform risk assessment and early intervention.