Intolerance of Uncertainty (IU), defined as the tendency to react negatively to uncertain situations, has gained recognition as a transdiagnostic factor implicated in various anxiety disorders. This systematic review explores the relationship between IU and anxiety disorders, emphasizing its conceptualization, measurement, and treatment. Anxiety disorders, including generalized anxiety disorder, social anxiety disorder, and obsessive-compulsive disorder, affect millions globally and significantly impair quality of life. Although existing treatments provide some relief, a deeper understanding of IU may enhance the development of targeted and effective interventions. This review systematically searched Scopus and Web of Science databases using predefined keywords related to "anxiety disorder" and "intolerance of uncertainty," yielding 2,299 initial records. Following a rigorous screening process based on PRISMA guidelines, including title/abstract screening, full-text review, and quality assessment, 42 studies met the inclusion criteria. The findings were organized into three main themes: (1) conceptualizing and measuring IU, including the development and validation of assessment tools; (2) examining IU in specific contexts and populations across developmental stages, catastrophic events and disorders; and (3) evaluating interventions targeting IU, such as Cognitive Behavioral Therapy (CBT), Acceptance and Commitment Therapy (ACT), and mindfulness-based approaches. Where applicable, quantitative synthesis explored correlations between IU and anxiety symptom severity. The review concludes that IU is a significant factor in the development and maintenance of anxiety disorders. Future research should focus on refining measurement tools, identifying mechanisms linking IU to specific anxiety presentations, and further developing targeted interventions. These findings have important implications for clinical practice and future research, underscoring the need to address IU in the treatment of anxiety disorders.
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