Patterns of marijuana use and physical health indicators among Canadian youth.

We examine how trajectories of marijuana use in Canadian youth (ages 15 to 28) are related to physical health indicators in adolescence and young adulthood. Youth were initially recruited in 2003 (N = 662; 48% male; ages 12 to 18) and followed for six waves. Five trajectories of marijuana use (Abstainers-29%, Occasional users-27%, Decreasers-14%, Increasers-20% and Chronic users-11%) were identified. Chronic users reported more physical symptoms, poorer physical self-concept, less physical activity, poorer eating practices, less sleep, and higher number of sexual partners during adolescence than other classes. Decreasers also reported poorer physical self-concept and poorer eating practices than abstainers. Other trajectory classes showed few significant health problems. Chronic users also reported more acute health problems (i.e. serious injuries, early sexual debut, higher number of sexual partners, greater likelihood of having a STI) in young adulthood than all other classes contributing to costs of healthcare. Youth who engage in early, frequent and continued use of marijuana from adolescence to young adulthood are at-risk of physical health problems in adolescence and young adulthood.