It is well known that psychosis is one of the most severe consequences related to cannabis consumption. Despite the clear negative impacts that this kind of drug abuse might exert upon users, the rates of consumption in Spain are alarmingly high and becoming a serious concern for both politicians and clinicians. Within the Psychiatry Service of the University Hospital Vall d’Hebron, a study has been conducted in order to assess the level of adherence to treatment. The study focuses on the use of group therapy, as an method to reduce cannabis dependence/consumption. Data from this study is presented as are various factors related to an improvement in the adherence to treatment are described.