While perceived harmfulness of marijuana use appears to be decreasing nationally among adolescents in the US, the passage of medical marijuana laws (MML) is associated with increases in perceived harmfulness among adolescents, according to a recent study. Marijuana use, it was also discovered, decreased among those who perceive marijuana to be harmful after passage of MML. Researchers conducted cross-sectional, nationally representative surveys of US students, conducted annually from 1991 to 2014. The sample included 1,134,734 adolescents in the 8^th, 10^th, and 12^th grades. They found:

• The perceived harmfulness of marijuana has decreased significantly since 1991 (from an estimated 84.0% in 1991 to 53.8% in 2014), and, across time, perceived harmfulness was lower in states that passed MML.

• In states with MML, perceived harmfulness of marijuana increased among 8^th graders after MML passage, while marijuana use decreased.

• Increased in perceived harmfulness among 8^th graders after MML passage was associated with ~33% of the decrease in use.