This thesis, titled "Effectiveness of a Brief Motivational Intervention for Change Processes in Colombian Young Marijuana Users," was authored by Luis Alberto Salinas Loaiza and directed by Patricia Hernández Zubieta. The study, conducted in 2016, evaluates the effectiveness of a brief motivational intervention for young Colombian marijuana users. The intervention was implemented using a workshop format and the Transtheoretical Model parameters. The study employed a pre-experimental design with pretest and posttest measurements (M1 X M2) on a single group. Instruments used included a survey on marijuana consumption expectations, the University of Rhode Island Change Assessment (URICA), the Inventory of Change Processes (IPC), and a follow-up interview. The results indicate that the intervention was effective for 28% of participants who are currently in maintenance, 36% who are in action with some difficulties, 87% who are in contemplation-action, and 18% who remain in precontemplation. The study concludes that the brief motivational intervention was effective for a significant portion of the targeted youth, particularly in promoting cognitive processes that lead to the consideration of quitting marijuana use.This thesis, titled "Effectiveness of a Brief Motivational Intervention for Change Processes in Colombian Young Marijuana Users," was authored by Luis Alberto Salinas Loaiza and directed by Patricia Hernández Zubieta. The study, conducted in 2016, evaluates the effectiveness of a brief motivational intervention for young Colombian marijuana users. The intervention was implemented using a workshop format and the Transtheoretical Model parameters. The study employed a pre-experimental design with pretest and posttest measurements (M1 X M2) on a single group. Instruments used included a survey on marijuana consumption expectations, the University of Rhode Island Change Assessment (URICA), the Inventory of Change Processes (IPC), and a follow-up interview. The results indicate that the intervention was effective for 28% of participants who are currently in maintenance, 36% who are in action with some difficulties, 87% who are in contemplation-action, and 18% who remain in precontemplation. The study concludes that the brief motivational intervention was effective for a significant portion of the targeted youth, particularly in promoting cognitive processes that lead to the consideration of quitting marijuana use.