"Consistent with the results of previous researchers,2 there was no evidence that the legalization of medical marijuana encourages marijuana use among youth. Moreover, the estimates reported in the Table showed that marijuana use among youth may actually decline after legalization for recreational purposes. This latter result is consistent with findings by Dilley et al4 and with the argument that it is more difficult for teenagers to obtain marijuana as drug dealers are replaced by licensed dispensaries that require proof of age.6"

Source

Anderson DM, Hansen B, Rees DI, Sabia JJ. Association of Marijuana Laws With Teen Marijuana Use: New Estimates From the Youth Risk Behavior Surveys. JAMA Pediatr. Published online July 08, 2019. doi:10.1001/jamapediatrics.2019.1720