Cannabis and Adolescent Motivation
"The apparent strength of these relationships in cross-sectional studies (e.g. Kandel, 1984) has been exaggerated because those adolescents who are most likely to use cannabis have lower academic aspirations and poorer high school performance prior to using cannabis than their peers who do not (Newcombe and Bentler, 1988). It remains possible that factors other than the marijuana use account for apparent causal relations. To the extent they may exist, these adverse effects of cannabis and other drug use upon development over and above the effect of pre-existing nonconformity may cascade throughout young adult life, affecting choice of occupation, level of income, choice of mate, and the quality of life of the user and his or her children."
Hall, W., Room, R., & Bondy, S., WHO Project on Health Implications of Cannabis Use: A Comparative Appraisal of the Health and Psychological Consequences of Alcohol, Cannabis, Nicotine and Opiate Use August 28, 1995 (Geneva, Switzerland: World Health Organization, 1998).