Street ketamine use and differential risk of suicidality among adults in Taiwan.

Introduction: The misuse of ketamine, a dissociative anesthetic, has surged sharply in popularity across East and Southeast Asia and Oceania. This study aimed to evaluate the association between recent patterns of ketamine use and the risk of suicide in northern Taiwan.

Methods: Illicit ketamine users were recruited through network-based sampling from 2015 to 2017, along with a comparison group of individuals who never used ketamine. Data on sociodemographics, drug use history, psychiatric disorders, and suicide risk were collected by trained psychiatric nurses. Participants were categorized into three groups: non- (n = 132), past (no ketamine use for ≥ 1 year; n = 80), and recent users (use in the past year; n = 167). Suicide risk, assessed by six items in the Mini-International Neuropsychiatric Interview, was classified as "no," "low," or "middle/high." Polytomous logistic regression and multivariate analyses were applied for risk estimation.

Results: Street ketamine users disproportionately experienced higher mental health disorders (e.g.,major depressive disorder), disadvantaged socioeconomic status, involvement in legal issues, and lifetime suicide attempts (25%). The prevalence of middle to high suicide risk was notably higher among recent (10.8%) and past (5.0%) ketamine users, compared with people who had no ketamine use history. Past-month suicidality was four times higher in recent users (95% CI 1.35-12.27) and 3.4 times higher in past users (95% CI 1.01-11.45). Excess risk associated with recent ketamine use manifested exclusively in suicidal ideation.

Discussion and conclusions: Illicit ketamine use is strongly linked to increased suicidality, especially among recent users. Even past users remain at higher risk, highlighting the importance of integrating suicide risk assessments and targeted interventions in community-based alcohol and drug services.