Abstract
<title>Abstract</title> <p>Background Substance use disorders and behavioural addictions represent a critical global public health challenge. Spiritual and religious factors have long been recognised as influential in both the development and resolution of addictive behaviours. Guilt and shame are moral emotions that frequently mediate the relationship between religion and addiction outcomes, yet their roles remain poorly integrated into theoretical models and clinical practice. No prior systematic review has simultaneously mapped the intersection of religion, spirituality, addiction, guilt, and shame across all three constructs. Methods A systematic review following PRISMA 2020 guidelines was conducted. Five databases were searched programmatically using Python 3.12 with 120 queries across 12 thematic blocks, supplemented by manual searches of nine biomedical, psychological, and religious databases. After screening 13,026 records, 100 studies published between 2000 and 2026 were included based on relevance to all three constructs, availability of full abstracts, and active digital object identifiers. Methodological quality was assessed using an adapted Mixed Methods Appraisal Tool (MMAT) across 10 criteria. Publication bias was evaluated using a proxy Egger regression test. Results Included studies spanned mixed methods and other designs (32%), longitudinal cohort studies (20%), qualitative studies (19%), cross-sectional surveys (14%), systematic reviews and meta-analyses (10%), and randomised controlled trials (5%). Alcohol use disorder (AUD) was the most studied addiction type (56%). Guilt, shame, and moral injury were the primary outcome focus in 44 studies. Twelve-Step and Alcoholics Anonymous (AA)/Narcotics Anonymous (NA) spirituality was the most examined religious dimension, featuring in 17 dedicated studies. Mean MMAT quality score was 6.3 out of 10, indicating moderate overall evidence quality. Egger's test revealed significant publication bias (intercept = -2.45, p < 0.001), reflecting disproportionate reporting of studies in which spirituality is protective against addiction. Conclusions Religion and spirituality exert complex, bidirectional effects on addiction outcomes. Guilt and shame operate as critical mediating mechanisms that can motivate recovery or entrench relapse depending on whether religious frameworks promote adaptive guilt with pathways to forgiveness, or maladaptive shame with no resolution. Integrating routine shame assessment and spiritually sensitive moral injury care into addiction treatment represents the priority clinical direction emerging from this review.</p>