According to the World Health Organization the population suffering from addiction problems is increasing. This population is characterized by multiple needs at the medico-psychosocial level. However, some of these patients, a particular subgroup that we are going to be interested in the so-called "high need" user group, find it difficult to access and stay in outpatient treatment programs. They often present a chaotic use of the health system, including a high number of hospitalizations in times of crisis. They also show very low utilization of health care services, accompanied by social marginalization. This can be related to relapses and poor social functioning. A high number of relapses occur particularly at the end of hospitalization. Interventions in the field of addiction, such as Transitional Case Management (TCM) should increase the adherence of these patients to treatment by accompanying them in the sensitive period following hospitalization. One of the objectives of the study is to evaluate the impact of TCM on the number, duration and type of hospitalizations, as well as the number of emergency room visits. The investigators will also measure the duration until the possible future hospitalization, after the TCM. The secondary objectives of this study will be to see the effect of TCM on adherence to outpatient treatment. The investigators will focus on the impact of follow-up on the participant's medico-psycho-social network, substance use and other psychological variables. The investigators will also evaluate his or her psychiatric symptoms and global and social functioning. Life satisfaction and satisfaction with the care received will also be measured. The investigators will compare the population treated by the TCM with the other users of the addiction service who are hospitalized. The study will investigate this through questionnaires at the beginning of care, at one month, three months, six months and 12 months after the start of TCM management.

Inclusion Criteria:

• Substance use disorder
• Hospitalisation at recruitment
• Substance Use Disorder according to the DSM-5 and one of the following criteria:
• No preexisting outpatient follow-up care or regular follow-up care
• More than three emergency room visits during the last 12 months
• More than three hospitalizations in psychiatric hospital during the last 12 months
• More than 40 hospitalization's days during the last 12 months
• First hospitalization for a SUD

Exclusion Criteria:

• Evidence of organic brain disease or learning disability based on the chart review.

Subgroup of high need users hospitalized in our addiction unit