Adolescence is a critical developmental period for the initiation of psychoactive substance use. Behaviour change theories are frequently used in prevention programmes, but their application across adolescent substance use prevention interventions has not been comprehensively mapped. To map theory-informed interventions for preventing psychoactive substance use among adolescents in school and community settings and to describe their theoretical foundations, characteristics and reported outcomes. A scoping review was conducted in accordance with Joanna Briggs Institute methodology and reported using PRISMA-ScR guidance. Searches of EMBASE, MEDLINE, PsycINFO, CINAHL and Web of Science were undertaken for studies published between 2000 and 2025. Eligible studies evaluated prevention interventions for adolescents aged 12 to 18 years in school or community contexts and explicitly reported a behavioural or social theory or model underpinning intervention design, content or delivery. Data were charted and synthesised descriptively. Eighteen studies met the inclusion criteria. Most interventions were school‑based and targeted multiple substances, particularly alcohol, tobacco and illicit drugs. Frequently used frameworks included the Theory of Planned Behaviour, Transtheoretical Model, Social Cognitive Theory and Health Belief Model, as well as applied approaches such as Motivational Interviewing and personality‑targeted cognitive behavioural models. Theory‑informed interventions were consistently associated with improvements in psychosocial determinants of substance use, including knowledge, attitudes, refusal skills and self‑efficacy. Evidence for sustained behavioural change was more variable and was often limited by short follow‑up periods. Selective personality‑targeted and culturally grounded interventions showed more consistent indications of longer‑term behavioural benefit. Theory‑informed adolescent substance use prevention interventions appear to strengthen psychosocial protective factors, but evidence of durable behavioural impact remains limited. Future prevention research should prioritise longer‑term follow‑up, cultural and contextual adaptation and stronger integration of family and community influences.