This study evaluates the effectiveness of a brief motivational intervention for change processes related to marijuana use among Colombian youth. The intervention, based on the Transtheoretical Model, was implemented through a workshop format. The results indicate that the intervention was effective for 28% of participants, who are now in the maintenance stage; partially effective for 36%, who are in the action stage; and generated cognitive processes leading to the contemplation-acting stage for 87% of participants. However, it was ineffective for 18% who remain in the precontemplation stage. The intervention affected change processes associated with marijuana use, showing effectiveness in the selected sample. The methodology used a pre-experimental design with pretest and posttest, and instruments included a survey on marijuana use expectations, the University of Rhode Island Change Evaluation Scale (URICA), the Change Process Inventory (IPC), and a follow-up interview. The study highlights the importance of motivational interventions in addressing substance use among youth, emphasizing the need for tailored approaches to different stages of change. The research contributes to understanding the effectiveness of brief motivational interventions in promoting behavior change related to marijuana use in young people.This study evaluates the effectiveness of a brief motivational intervention for change processes related to marijuana use among Colombian youth. The intervention, based on the Transtheoretical Model, was implemented through a workshop format. The results indicate that the intervention was effective for 28% of participants, who are now in the maintenance stage; partially effective for 36%, who are in the action stage; and generated cognitive processes leading to the contemplation-acting stage for 87% of participants. However, it was ineffective for 18% who remain in the precontemplation stage. The intervention affected change processes associated with marijuana use, showing effectiveness in the selected sample. The methodology used a pre-experimental design with pretest and posttest, and instruments included a survey on marijuana use expectations, the University of Rhode Island Change Evaluation Scale (URICA), the Change Process Inventory (IPC), and a follow-up interview. The study highlights the importance of motivational interventions in addressing substance use among youth, emphasizing the need for tailored approaches to different stages of change. The research contributes to understanding the effectiveness of brief motivational interventions in promoting behavior change related to marijuana use in young people.