evidence: One of the top priorities among cannabis researchers is clarifying how the drug—which has been legalized for recreational use in 21 states and for medical use in 37 states—affects the developing brain. "I’m concerned by the increase in the number of people who are using cannabis at higher doses on a daily basis," said Nora Volkow, MD, director of the National Institute on Drug Abuse (NIDA). "Adolescents are more vulnerable to addiction, and once they are using compulsively, cannabis can interfere with memory and learning." In one study, 15% of people of all ages who used cannabis in the past 30 days met the Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition) criteria for cannabis use disorder, and rates specifically among youth ages 12 to 20 were significantly higher at 23% (Richter, L., et al., The American Journal of Drug and Alcohol Abuse, Vol. 43, No. 3, 2017).