INTRODUCTION: The aim of this systematic review was to assess the effectiveness of brief interventions realized in primary care in reducing cannabis use for adolescents and emerging adults. METHODS: PubMed, CINAHL, Embase, PsycInfo, and Central (Cochrane Library) were searched until December 2020. Randomized controlled trials conducted in primary care, concerning in-person brief interventions for non-medical cannabis users aged from 12 to 25 years old were eligible for inclusion. Brief interventions had to last 30 min or less. Patients with comorbid mental health disorder or very specific populations were not included. RESULTS: One thousand eighty hundred and fifty-five studies were identified through database searching; only 8 studies involving 2,199 patients were included for qualitative synthesis after double reading and data extraction. Randomized controlled trials selected were heterogeneous regarding screening tools, initial levels of cannabis use and cannabis outcomes measures. Brief interventions were all based on motivational interviewing techniques or personalized feedback. Seven studies consisted in a single session of brief intervention. Six studies involved also other substance users. No significant reduction of cannabis use after brief intervention was found for most studies, especially in the long term. A trend of decreased cannabis consequences, such as negative psychosocial repercussions, perception of cannabis use by peers, or driving under the influence of cannabis, was reported. CONCLUSION: The current state of knowledge does not allow us to say that the brief intervention is effective in reducing cannabis use among adolescents in primary care. We found a mild positive effect on cannabis consequences after brief intervention. Mixed qualitative and quantitative studies are need to better evaluate the impact of brief intervention and his faisability. PROSPERO (International Prospective Register of Systematic Reviews): n° CRD42016033080.Read less <