Background <p>Incarcerated individuals with substance use disorders face a high risk of relapse in the absence of structured, motivational, and context-adapted interventions. This study examined changes associated with the implementation of a Relapse Prevention Program designed to enhance motivation for change, anticipate early warning signs of relapse, and strengthen adaptive coping strategies. The intervention integrated Marlatt and Gordon’s Relapse Prevention Model with the COM-B framework (Capability, Opportunity, and Motivation) and Michie’s Behaviour Change Wheel, constituting an original proposal in prison settings.</p> Results <p>A pre–post quasi-experimental design was conducted with participants from three prison units. Outcome measures included the SOCRATES 8D scale (motivation), the AWARE scale (perceived relapse risk), and the Brief COPE inventory (coping strategies). The findings indicated preliminary improvements in motivation for change, particularly in problem recognition and action steps. Improvements were also observed in adaptive coping strategies, including active coping, positive reframing, and planning. No significant changes were detected in perceived relapse risk. Female participants showed greater improvements in coping strategies and lower post-intervention substance use.</p> Conclusions <p>These findings support the feasibility and clinical applicability of the program in prison settings. The results underscore the importance of integrating emotional regulation components and a gender-responsive perspective into relapse prevention programmes for incarcerated individuals with substance use disorders.</p>