Patterns and implications of co-use between vaping and hallucinogens: a systematic review and meta-analysis.
BACKGROUND: The co-occurrence use of e-cigarettes and hallucinogens has become increasingly common, particularly among youth and young adults. However, evidence regarding the association between these behaviors remains limited and fragmented. This systematic review and meta-analysis aimed to synthesize current evidence, examining the correlation between hallucinogen use and the likelihood of being an e-cigarette user. METHODS: A comprehensive search was conducted in PubMed, Scopus, Web of Science, EMBASE, and Cochrane CENTRAL up to June 2025. Eligible studies measured both hallucinogen and e-cigarette use and reported quantitative associations between these behaviors. Data extraction and risk-of-bias assessments were performed independently by three reviewers using the Newcastle-Ottawa Scale. Pooled effect sizes were calculated using a random-effects model (REML). Certainty of evidence was evaluated with the GRADE approach. RESULTS: Eleven studies met the inclusion criteria (n = 247,904), and seven were included in the meta-analysis (n = 217,478). The pooled analysis demonstrated that hallucinogen users had 4.47 times higher odds of being e-cigarette users (OR: 4.47, 95% CI 2.72 to 7.34; p < 0.001; I2 = 95.7%, n = 7). The certainty of evidence was rated as low. CONCLUSIONS: Hallucinogen use is directionally and strongly associated with e-cigarette use across diverse populations. Although the direction of association was consistent across studies, the magnitude of effect was heterogeneous. These behaviors likely share psychosocial and environmental determinants, although alternative explanations, including shared genetic liability, recall bias, and residual confounding, cannot be excluded. Further longitudinal studies are needed to clarify the underlying mechanisms of this association and establish temporality. The findings also support integrating hallucinogen-use screening into e-cigarette prevention and harm-reduction programs targeting youth and young adults.