PURPOSE Brief intervention to reduce cannabis is a promising technique that could be adapted for use in primary care, but it has not been well studied in this setting. We tested the efficacy of a brief intervention conducted by general practitioners among cannabis users aged 15 to 25 years. METHODSWe performed a cluster randomized controlled trial with 77 general practitioners in France. The intervention consisted of an interview designed according to the FRAMES (feedback, responsibility, advice, menu, empathy, selfefficacy) model, while the control condition consisted of routine care. RESULTSThe general practitioners screened and followed up 261 young cannabis users. After 1 year, there was no significant difference between the intervention and control groups in the median number of joints smoked per month among all users (17.5 vs 17.5; P = .13), but there was a difference in favor of the intervention among nondaily users (3 vs 10 ; P = .01). After 6 months, the intervention was associated with a more favorable change from baseline in the number of joints smoked (-33.3% vs 0%, P = .01) and, among users younger than age of 18, smoking of fewer joints per month (12.5 vs 20, P = .04).CONCLUSIONS Our findings suggest that a brief intervention conducted by general practitioners with French young cannabis users does not affect use overall. They do, however, strongly support use of brief intervention for younger users and for moderate users. INTRODUCTIONC annabis is the first illegal substance used by young people worldwide.1 Across continents, 7% to 12% of adolescents and teenagers younger than 18 years and 6.6% to 25% of young adults aged 18 to 25 years are monthly users. [1][2][3][4] In Europe, France has the highest consumption of cannabis.3 As of 2014, 25.5% of French adolescents (aged 15 to 17 years) and 17% of young adults (aged 18 to 25 years) were monthly users of cannabis. 5,6 Current data are clear about the risks of cannabis use, 7 which include social and psychiatric risks (eg, anxiety, depression, and an increased incidence of schizophrenia in vulnerable individuals), 8,9 risks of lung and otorhinolaryngeal cancers, 10,11 and cardiovascular risk. [12][13][14] Use before driving increases the likelihood of motor vehicle collision-related morbidity and mortality. [15][16][17][18] During adolescence, cannabis use causes cerebral microstructural changes that are not always reversible and have been implicated in cognitive and psychiatric disorders. 19 In France, 80% of youth aged 15 to 25 years have visited their general practitioner in the preceding year.5 These visits could represent a privileged opportunity to identify young cannabis users and intervene to reduce their consumption. Motivational interviewing is a method of interaction centered on the patient and intended to modify behavior. 33,34 or the general public following media calls for participation. [35][36][37][38][39][40] The initial levels of consumption varied greatly, from once a year 19 to weekly 11,13,14,16 to monthly, [20][21][22]...