Cannabis use and later life outcomes
David M. Fergusson & Joseph M. Boden
Addiction, 2008, 103, 969–976
doi : 10.1111/j.1360-0443.2008.02221.x
Aim : To examine the associations between the extent of cannabis use during adolescence and young adult-hood and later education, economic, employment, relationship satisfaction and life satisfaction outcomes. Design A longitudinal study of a New Zealand birth cohort studied to age 25 years.
Measurements : Measures of : cannabis use at ages 14–25; university degree attainment to age 25; income at age 25; welfare dependence during the period 21–25 years; unemployment 21–25 years; relationship quality; life satisfaction. Also, measures of childhood socio-economic disadvantage, family adversity, childhood and early adolescent behavioural adjustment and cognitive ability and adolescent and young adult mental health and substance use.
Findings : There were statistically significant bivariate associations between increasing levels of cannabis use at ages 14–21 and: lower levels of degree attainment by age 25 (P < 0.0001); lower income at age 25 (P < 0.01); higher levels of welfare dependence (P < 0.0001); higher unemployment (P < 0.0001); lower levels of relationship satisfaction (P < 0.001); and lower levels of life satisfaction (P < 0.0001). These associations were adjusted for a range of potentially confounding factors including: family socio-economic background; family functioning; exposure to child abuse; childhood and adolescent adjustment; early adolescent academic achievement; and comorbid mental disorders and substance use. After adjustment, the associations between increasing cannabis use and all outcome measures remained statistically significant (P < 0.05).
Conclusions : The results of the present study suggest that increasing cannabis use in late adolescence and early adulthood is associated with a range of adverse outcomes in later life. High levels of cannabis use are related to poorer educational outcomes, lower income, greaterwelfare dependence and unemployment and lower relationship and life satisfaction. The findings add to a growing body of knowledge regarding the adverse consequences of heavy cannabis use.
Keywords : Cannabis use, education, life satisfaction, longitudinal study, mental health, unemployment, welfare
In recent years, there have been growing concerns and debates about the effects of cannabis use on the health and well being of young people. These concerns have been motivated by evidence of growing cannabis use in young people [1,2], changes in the nature and strength of cannabis [3,4] and by growing evidence linking cannabis to mental health and other problems [1,5–9].While the role of cannabis in encouraging psychosocial problems in young people remains controversial, there is growing evidence from both epidemiology and neuroscience that cannabis may be more harmful than believed previously [10,11].
An aspect of these concerns that requires further attention is the extent to which the use, and in particular heavy use, of cannabis may have adverse consequences for a number of important life-course outcomes, including educational achievement, income, welfare dependence, unemployment, relationship satisfaction and life satisfaction. Specifically, there have been frequent references in the literature on cannabis to suggest that cannabis use may reduce educational achievement [12–14], increase welfare dependence , reduce income  and lead to impaired interpersonal relationships . While there is some evidence of statistical linkage with these outcomes, it may be suggested that the apparent associations between cannabis use and these life-course outcomes may reflect the presence of uncontrolled sources of confounding .
In this study, we use data gathered over the course of a 25-year longitudinal study to examine the linkages between cannabis use prior to the age of 21 and subsequent life-course outcomes including: educational achievement, income, welfare dependence, unemployment, relationship satisfaction and life satisfaction. The aims of the analysis are to document the associations between cannabis use by 21 and subsequent life history, and to examine the extent to which these associations may be explained by confounding factors that were associated with patterns of cannabis use in adolescence and young adulthood.