Rationale: Advancing marijuana prevention and intervention efforts are important given the decreasing perception of harm among adolescents and increasing marijuana legalization. Objectives: This study evaluates how a monitored abstinence protocol may contribute to emotional functioning and changes in marijuana problems that can enhance successful outcomes for non-treatment-seeking adolescent marijuana users. Methods: Adolescent marijuana users (n = 26) and demographically matched controls (n = 30) completed 28 days of monitored abstinence confirmed by biweekly urine toxicology. Participants were given measures of emotional functioning, marijuana use symptoms, and reward sensitivity during monitored abstinence. Results: All participants (n = 56) completed the protocol, and 69% of marijuana users (n = 18 of 26) were confirmed abstinent for 28 days, with all users showing decreasing marijuana use. Reductions in subsyndromal depression, positive marijuana use expectancies, and poor sleep quality were observed by the end of the monitored abstinence period (n = 26, p values < .05). Marijuana users also reported more attentional impulsivity and less responsiveness to reward stimuli during the second week of abstinence compared to controls. Later age of onset of regular marijuana use and more cumulative lifetime use were associated with a greater degree of emotional change and increased recognition of the negative effects of marijuana use. Conclusions: Monitored abstinence programs may be beneficial in reducing marijuana use, subsyndromal emotional distress symptoms, and changing beliefs about marijuana use. Future prevention and intervention efforts may consider targeting reward sensitivity and impulsivity, in addition to marijuana use, expectancies, and emotional functioning.