Meeting adherence is an important element of compliance in treatment programmes. It is influenced by several factors one being self-efficacy. We aimed to investigate the association between self-efficacy and meeting adherence and other factors of importance for adherence among patients with alcohol and drug addiction who were undergoing an intensive lifestyle intervention. The intervention consisted of a 6-week Very Integrated Programme. High meeting adherence was defined as >75% participation. The association between self-efficacy and meeting adherence were analysed. The qualitative analyses identified themes important for the patients and were performed as text condensation. High self-efficacy was associated with high meeting adherence (ρ = 0.24, p = 0.03). In the multivariate analyses two variables were significant: avoid complications (OR: 0.51, 95% CI: 0.29-0.90) and self-efficacy (OR: 1.28, 95% CI: 1.00-1.63). Reflections on lifestyle change resulted in the themes of Health and Wellbeing, Personal Economy, Acceptance of Change, and Emotions Related to Lifestyle Change. A higher level of self-efficacy was positively associated with meeting adherence. Patients score high on avoiding complications but then adherence to the intervention drops. There was no difference in the reflections on lifestyle change between the group with high adherence and the group with low adherence.