This paper is a retrospective study with a five year follow-up which examines the variations in substance use and the determinants of these variations. This exploratory research studied a sub-sample of 22 participants, selected from an initial sample of 197 patients with concurrent substance use and other mental health disorders. At the quantitative level, the statistical analysis shows an improvement in the problematic use of alcohol and drugs but no change in psychological state, health, family and interpersonals relations, as well as employment. At the qualitative level, the analysis of the participant's subjective view indicates that the two main elements of progression in substance use are the effects and the availability of substances. The main elements of reduction in substance use are the use of services, the personal techniques developed by participants, the family network, physical health, lack of financial resources, "occupational" activities, and a process of maturation.