Using marijuana just once or twice a month is associated with worse school performance and emotional distress for teens, according to a large national study of adolescents led by Ryan Sultán, an assistant professor of clinical psychiatry at Columbia University Vagelos College of Physicians and Surgeons. The more frequently teens used cannabis, the more likely they were to report emotional distress and other social and academic problems.

“While previous studies have focused on the effects of frequent cannabis use among teens, our study found that any amount of cannabis use at all may put kids at risk of falling behind in school, and the kids using most often may have the greatest risk,” says Sultán, who studies adolescent substance use and is also a child and adolescent psychiatrist with Columbia and the Center for Youth Mental Health at NewYork-Presbyterian. “A few ‘harmless’ joints can snowball into real academic consequences. Teens using it regularly often struggle to focus, miss school, and may lose interest in their future plans.”