Abstract
QUESTION: The rising prevalence of mental health conditions and a global treatment gap demand new solutions that address symptoms and foster psychological well-being. Just-in-time adaptive interventions (JITAIs) and ecological momentary interventions (EMIs) are emerging mobile health approaches, providing real-time, personalised support. However, the effectiveness of current JITAIs/EMIs and the longevity of effects remain uncertain. STUDY SELECTION AND ANALYSIS: Studies investigating the effectiveness of JITAIs/EMIs for depression, anxiety and indicators of psychological well-being, published between 2018 and May 2025, were eligible. Following the standards for reporting (Preferred Reporting Items for Systematic Reviews and Meta-Analyses; PRISMA) and quality assessment (Risk of Bias; RoB), a total of K=23 studies and N=2563 individuals (71.7% female) were included. FINDINGS: JITAIs/EMIs showed a small between-group effect (g=0.15, 95% CI 0.05 to 0.26, p=0.003). Nine studies reported follow-up effects (mean follow-up time M=3.06 months, SD=2.21) with significant results at 1 and 3-6 months. Interventions shorter than 6 weeks yielded greater longevity of effects (g=0.71, 95% CI 0.18 to 1.24, p=0.008). Funnel plots and sensitivity analyses confirmed robustness of findings. Risk of bias was moderate to high for intervention adherence and missing outcome data. CONCLUSIONS: Currently existing JITAIs and EMIs slightly improve mental health, particularly mental illness, with long-term effects up to 6 months. A clear definition of JITAIs and decision rules, research on long-term effects and careful selection of control conditions are needed.