This is a preprint of an article published in Addiction
© 2008 Society for the Study of Addiction
Fergusson DM, Boden JM. Cannabis use and later life outcomes
Addiction 103: 969-976
Cannabis use and later life outcomes
David M. Fergusson, PhD
Joseph M. Boden, PhD
University of Otago, Christchurch School of Medicine and Health Sciences
Corresponding author: Prof. David M. Fergusson, Christchurch Health and Development Study,
University of Otago, Christchurch School of Medicine and Health Sciences, PO Box 4345,
Christchurch, New Zealand
Phone: +64 3 372 0406 Fax: +64 3 372 0407 Email: email@example.com
Word count: 2811
Cannabis use and later life outcomes
David M. Fergusson and Joseph M. Boden
Aim: To examine the associations between the extent of cannabis use during adolescence and
young adulthood and later education, economic, employment, relationship satisfaction, and life
Design: A longitudinal study of a New Zealand birth cohort (N = 1063) studied to age 25.
Measurements: Measures of: 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 socioeconomic 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 15-21 and: lower levels of degree attainment by age 25 (p < .0001); lower
income at age 25 (p < .01); higher levels of welfare dependence (p < .0001); higher unemployment
(p < .0001); lower levels of relationship satisfaction (p < .001); and lower levels of life satisfaction
(p < .0001). These associations were adjusted for a range of potentially confounding factors
including: family socioeconomic 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 < .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, greater welfare
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, mental health, education, unemployment, welfare, life satisfaction,
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 previously believed (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,
13), increase welfare dependence (14), reduce income (15), and lead to impaired interpersonal
relationships (16). While there is some evidence of statistical linkage between 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 (17).
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.
The data were gathered during the course of the Christchurch Health and Development Study
(CHDS). In this study a birth cohort of 1265 children (635 males, 630 females) born in the
Christchurch (New Zealand) urban region in mid-1977 has been studied at birth, 4 months, 1 year
and annually to age 16 years, and again at ages 18, 21 and 25 years(18, 19). The analyses were
based on the 1003 study participants for whom information was available for outcomes at ages 21-
25 years (79% of the original sample). All study information was collected on the basis of signed
and informed consent from study participants.
Estimated amount of cannabis use, ages 15-21
At the age 15, 16, 18, and 21 year assessments, participants were questioned as to the number of
occasions on which they had used cannabis during each year. For the purposes of the present study,
these estimates were summed for the period 15 to 21 years to arrive at an estimate of the total
number of times participants had used cannabis during the period 15-21 years (M = 74.98, SD =
134.80). The estimate of the total number of times participants had used cannabis during the period
15-21 years was then used to classify participants using a categorical measure of total cannabis use,
ranging from 1 (never used cannabis) to 6 (used cannabis 400+ times).
In addition, two further measure of frequency of cannabis use were created. First, the
annual data on the amount of cannabis use were classified into a series of class intervals as follows:
did not use cannabis during the year; used less than monthly on average (1-11 times); used at least
monthly on average (12-50 times); used at least weekly on average (more than 50 times). These
were then averaged over the period 15-21 years to arrive at an estimate of the average frequency of
cannabis use during the period 15-21 years. Second, an estimate of the number of occasions on
which participants had used cannabis during the period 15-18 years was calculated by summing the
annual estimates of cannabis use for the period 15-18 years.
Education/Income. At ages 21 and 25, cohort members were questioned concerning their history of
enrolment in tertiary education and training and any educational/vocational qualifications obtained.
This information was used to classify participants on a dichotomous measure of degree (Bachelor’s
level or above) attainment prior to age 25 years. Also at age 25, participants were asked to estimate
their personal gross income from all sources over the previous 12 months. This estimate served as
the measure of personal income (in New Zealand dollars) at age 25 (M = 28,539; SD = 18,688).
Welfare dependence/unemployment. Participants were questioned at age 25 about their receipt of
social welfare benefits during the period 21-25 years. The percentage of cohort members who
reported receiving an unemployment benefit, domestic purposes benefit (available to single parents
with dependent children), or a sickness or invalids’ benefit at any point in the period 21-25 years
served as the outcome measure. In addition, participants were also questioned as to their patterns of
employment and unemployment during the period 21 to 25 years. Participants who reported being
unemployed at any time during the period 21 to 25 years were classified as having been
unemployed at some point by age 25.
Relationship and life satisfaction. Relationship satisfaction was assessed using the 25-item Intimate
Relations Scale (20). Participants were asked to respond to the measure with reference to their most
recent intimate romantic relationship of one month or longer duration at age 25. This measure was
scaled so that higher scores on the measure reflected greater levels of relationship satisfaction. Life
satisfaction at age 25 was assessed on the basis of 12 custom-written items assessing satisfaction
with a range of life domains, including work, family, friends, leisure pursuits, and life in general.
Participants responded to the items on a four point scale ranging from very happy to very unhappy.
For the purposes of the present analysis, scale scores were created by summing the responses to the
12 items to create a general life satisfaction measure for each age. This measure was scaled so that
lower scores on the measure reflected greater levels of life satisfaction.
A range of covariate factors were chosen for the analyses, based on: (a) their correlation with
cannabis use at ages 15-21; and (b) previous research on the present cohort suggesting that the
factors were related to both cannabis use and later life outcomes. The following covariate factors
were chosen for inclusion in the analyses:
Socioeconomic status of family of origin. These measures included maternal age, maternal
education, socioeconomic status at birth, and average standard of living at ages 0-10.
Family functioning. These measures included an overall measure of family adversity, a
measure of the number of parental changes to age 15, parental alcoholism, parental illicit drug use,
and parental offending.
Exposure to child abuse. Measures of exposure to childhood (prior to age 16) sexual abuse
and physical punishment were included in the analyses.
Childhood and adolescent adjustment. These measures included a measure of conduct
problems at ages 7-13, a measure of attention problems at ages 7-13, a measure of parental
attachment at age 14, and a measure of the extent to which the individual associated with deviant
peers during the period 15-21 years.
Adolescent academic achievement. These measures included a measure of cognitive ability
at age 13, and a measure of overall grade point average at ages 11-13.
Comorbid mental health disorders and substance use. The measures included a summary
measure of other illicit drug use during ages 15-21; a summary of the frequency of alcohol
consumption during ages 15-21; a summary of the frequency of cigarette smoking during ages 15-
21; and a summary measure of major depression over the period 15-21 years.
The associations between cannabis use during the period 15-21 years and outcomes from ages 21-
25 were tested for linear trend using the Mantel-Haenszel chi square test of linear trend for
percentage outcomes, and by one-way analysis of variance for means. In order to adjust the
associations for potentially confounding factors, logistic regression (for dichotomous outcomes) and
multiple regression (for continuous outcomes) models were fitted to the data, using forward and
backward methods of covariate inclusion in order to arrive at stable models. Tests of statistical
significance for the adjusted associations were given by the Wald chi square measure of association
for percentage outcomes, and t-tests for continuous outcomes. Then, adjusted associations between
cannabis use during the period 15-21 years and later outcomes were computed using the methods
described by Lee (21).
In addition, in order to examine the robustness of the analyses to alternative forms of
classification of cannabis use, the above analyses were repeated using an alternative method of
classifying cannabis consumption during the period 15-21 years. In these analyses, cannabis
consumption was represented by a measure of frequency with which participants used cannabis
during each year during the period 15-21 years, averaged over those years.
Finally, to examine the extent to which early (prior to age 18) cannabis consumption was
associated with later adverse outcomes, the analyses above were repeated using a measure of total
cannabis consumption during the period 15-18 years.
Associations between cannabis use by age 21 and life outcomes at age 25.
Table 1 shows the cohort classified into six groups based on the estimated amount of cannabis used
by age 21. These groups range from non-users, to those who had used cannabis on more than 400
occasions prior to age 21. For each group, the Table reports on measures of a series of outcome
variables, including: university degree attainment by age 25; income at age 25; welfare dependence
during the period 21-25 years; unemployment during the period 21-25 years; relationship
satisfaction at age 25, and overall life satisfaction at age 25. In all cases, results were tested for
linear trend (see Methods). The Table shows that the increasing use of cannabis prior to the age of
21 was associated with declining levels of degree attainment (p < .0001), declining income (p <
.01), increasing welfare dependence (p < .0001), increasing unemployment (p < .0001), declining
relationship satisfaction (p < .001), and declining life satisfaction (p < .0001).
INSERT TABLE 1 HERE
Associations between cannabis use by age 21 and life outcomes at age 25, adjusted for
confounding factors and comorbid mental health disorders and substance use
One explanation for the pattern of associations shown in Table 1 is that these reflect the presence
selection and confounding processes relating to both cannabis use and life course choices and
decisions. To address issues of confounding, the results were adjusted for a large number of
covariate factors by fitting logistic regression and multiple regression models to the data, including
covariate factors. These covariates included measures of the socio-economic background of the
family of origin, measures of family functioning and exposure to adversity, exposure to child
sexual and physical abuse, measures of childhood and adolescent adjustment, measures of
academic achievement in early adolescence, and measures of comorbid mental health disorders and
Table 2 shows the associations between cannabis use by the age of 21 and outcomes during
the period 21-25 years, adjusted for the covariate factors and comorbid mental health disorders and
substance use. This Table shows that, even following extensive adjustment for prospectively-
assessed covariate factors there were still significant trends for increasing cannabis use to be
associated with lower levels of degree attainment (p < .01), lower income (p < .01), higher levels of
welfare dependence (p < .0001), higher levels of unemployment (p < .01), lower levels of
relationship satisfaction (p < .05), and lower overall life satisfaction (p < .01).
INSERT TABLE 2 HERE
In order to examine the robustness of the above findings to alternative classifications of cannabis
consumption, the analyses above were repeated using a measure of the estimated cannabis
consumption during each year, averaged over the period 15-21 years (see Methods). These analyses
revealed the following pattern of results:
1. Increasing frequency of cannabis use during the period 15-21 years was significantly associated
with the following outcome measures by age 25: lower levels of degree attainment (p < .0001),
lower income (p < .01), higher welfare dependence (p < .0001), higher unemployment (p <
.0001), lower levels of relationship satisfaction (p < .001), and lower levels of overall life
satisfaction (p < .0001).
2. After adjustment for confounding factors, frequency of cannabis use during the period 15-21
years remained significantly associated with lower levels of degree attainment (p < .01), lower
income (p < .01), higher welfare dependence (p < .0001), higher unemployment (p < .05), and
lower levels of relationship satisfaction (p < .05) and overall life satisfaction (p < .0001).
The results of this analysis suggest that the findings of a persistent association between cannabis use
and later adverse outcomes are robust to alternative methods of classifying cannabis use.
In addition, in order to examine the extent to which early (prior to age 18) cannabis use was
associated with later adverse outcomes, the analyses reported above were repeated using a measure
of the amount of cannabis used during the period 15-18 years, in place of the measure of cannabis
use during the period 15-21 years (see Methods). In general, the results of the analyses were
congruent with those using the age 15-21 measure of cannabis use, although the associations
between cannabis use at ages 15-18 and later outcomes were somewhat weaker than the
associations between cannabis use at ages 15-21 and later outcomes. After control for confounding,
each of the outcome measures remained significantly (p < .05) associated with the amount of
cannabis use during ages 15-18.
This research has used data gathered over the course of a 25-year longitudinal study to examine the
relationship between the use of cannabis up to the age of 21 and subsequent life outcomes
including: educational achievement, income, welfare dependence, partnership relationships, and life
satisfaction. This analysis showed that, even following extensive control for factors present prior to
and during adolescence, increasing cannabis use was associated with: declining educational
achievement; reduced income at 25; increased welfare dependence; reduced relationship
satisfaction; and reduced life satisfaction. These results were found to be robust to alternative
methods of classifying cannabis use prior to age 21. Similar, but slightly less marked results were
observed for cannabis use by the age of 18.
These results are consistent with at least three explanations of the association between
cannabis use and life outcomes. First, these associations may be explained by residual
confounding. Although we were able to control a wide range of confounding factors, including
both factors antecedent to cannabis use, and comorbid substance use and mental health disorders,
the possibility remains that the observed associations may be explained by non-observed sources of
confounding (17). Second, the results may reflect the consequences of cannabis use for
neuropsychological functioning. This conjecture is supported by a growing body of evidence that
suggests that the use of cannabis may lead to both acute and long term changes in the structure and
function of the brain (22-24). Third, the origins of these associations may be social rather than
biological. In particular, cannabis use is more frequent in social contexts which may encourage
what have been described by Kandel and colleagues as “anticonventional” attitudes (25). Given
this, it may be suggested that the apparent linkages between cannabis use and life course outcomes
are in fact symptomatic of the greater participation of cannabis users in social contexts that
discourage educational achievement and material success.
Which, if any, of these explanations holds is unclear. Nonetheless, the findings in this
study are consistent with a growing body of evidence that has raised concerns about the extent to
which cannabis use may have adverse psychosocial consequences that span: increased risks of
psychotic illness (6); increased risks of depression and other mental illness (1, 7); and increased
risks of other illicit substance use (9) . These recent findings have raised a strong challenge to the
view that cannabis is a relatively harmless drug, and suggest that the heavy use of cannabis may
have multiple adverse consequences. While there have been suggestions that these associations can
be explained by residual confounding (17), it is notable that despite extensive efforts at statistical
control in a growing number of studies, this has not been shown to be the case.
These findings are, of course, subject to a number of limitations. First, they report on the
experiences of a particular group of individuals born at a specific time and reared in a specific
social context. Second, the results are based on self-report data, and thence will be subject to errors
of reporting and reminiscence. Third, as noted above, the results may be subject to residual
confounding. Nonetheless, within these limitations, the results of the present study suggest that the
increasing use of cannabis in adolescence may result in longer-term educational, economic and
personal disadvantage in young adulthood.
Acknowledgements: This research was funded by grants from the Health Research Council of New
Zealand, the National Child Health Research Foundation, the Canterbury Medical Research
Foundation and the New Zealand Lottery Grants Board.
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Table 1. Associations between level of cannabis use, ages 15-21, and life outcomes ages 21-25.
Number of occasions using cannabis ages 15-21
(n = 319)
(n = 450)
(n = 74)
(n = 62)
(n = 44)
(n = 54)
% Gained university degree by age 25 35.9 27.1 18.3 10.5 9.1 1.9 <.0001
Mean (SD) personal income age 25
% Welfare dependent ages 21-25 25.0 31.7 40.9 52.6 54.6 57.7 <.0001
% Unemployed ages 21-25 21.3 23.2 25.4 42.1 40.9 51.9 <.0001
Mean (SD) relationship qualtity score
Mean (SD) life satisfaction score age 252 19.9
1 Mantel-Haenszel χ2 test of linear trend for percentages; one-way ANOVA for means.
2 Higher scores indicate lower levels of life satisfaction.
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Table 2. Associations between level of cannabis use, ages 15-21, and life outcomes ages 21-25, after adjustment for confounding factors and comorbid
mental health disorders and substance use1.
Number of occasions using cannabis ages 15-21
% Gained university degree by age 25 32.7 29.1 25.5 22.2 19.2 16.4 <.01
Mean personal income age 25 (in
% Welfare dependent ages 21-25 21.1 26.4 32.5 39.2 46.4 53.7 <.0001
% Unemployed ages 21-25 18.4 22.1 26.3 30.9 36.1 41.4 <.01
Mean relationship quality age 25 26.1 25.6 25.1 24.9 24.1 23.7 <.05
Mean life satisfaction score age 253 20.0 20.3 20.7 21.0 21.4 21.7 <.01
1 Factors included: maternal age; maternal education; family socioeconomic status at birth; average family standard of living (ages 0-10); exposure to
childhood sexual and physical abuse; parental changes by age 15; family adversity; parental illicit drug use; parental criminality; parental alcoholism;
parental attachment (age 14); conduct problems (ages 7-13); attention problems (ages 7-9); association with deviant peers (ages 15-21); cognitive
ability score (age 13); grade point average (ages 11-13); other illicit drug use (ages 15-21); frequency of alcohol use (ages 15-21); frequency of
cigarette smoking (ages 15-21); major depression (ages 15-21).
2 Wald χ2 for percentages; t-test for means.
3 Higher scores indicate lower levels of life satisfaction.