The study found that those who started using cannabis before age 15 and used it frequently at age 21 were more likely to report symptoms of AD in early adulthood. This link was similar in magnitude for those who had only used cannabis and those who reported having used cannabis along with other illicit drugs. This association between early-onset and frequent use of cannabis and symptoms of AD was independent of individual and family backgrounds and the use of other illicit drugs. Because both cannabis use and AD are common events, this association is a serious public health concern. Further research is needed in order to replicate and confirm these findings. Data were collected on a cohort of 3,239 Australian young adults, who were monitored from birth to age 21. At age 21, data on AD were obtained from the sample, along with information on their use of cannabis at age 21. Potential confounding factors were prospectively measured when the child was born and at age 14. Confounding factors were the child's gender, mother's age and education, maternal marital status and quality, family income, maternal mental health, maternal substance use, adolescent's mental health, and adolescent smoking status and alcohol consumption at age 14. 1 figure, 4 tables, and 38 references