National Addiction Centre, Institute of Psychiatry, London
Department of Child Psychiatry, Institute of Psychiatry, London
Leicester Royal Infirmary, University of Leicester
Royal Free and University College Medical School, London
Institute of Psychiatry, London
Office for National Statistics, London, UK
Correspondence: Annabel Boys, National Addiction Centre, 4 Windsor Walk, London SE5 8AF, UK. E-mail: a.boys{at}iop.kcl.ac.uk
Declaration of interest None. Funding details in Acknowledgements.
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ABSTRACT |
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Aims To determine which of alcohol, nicotine and cannabisis mostclosely linked to psychiatric disorders in early adolescence.
Method Data from 2624 adolescents aged 1315 years were drawn from a national mental health survey of children. The relationship between psychiatric morbidity and smoking, drinking and cannabis use was examined by logistic regression analyses.
Results Having a psychiatric disorder was associated with an increased risk of substance use. Greater involvement with any one substance increased the risk of other substance use. Analyses of the interactions between smoking, drinking and cannabis use indicated that the relationship between substance use and psychiatric morbidity was primarily explained by regular smoking and (to a lesser extent) regular cannabis use.
Conclusions In this sample, links between substance use and psychiatric disorders were primarily accounted for by smoking.The strong relationship is likely to be due to a combination of underlying individual constitutional factors and drug-specific effects resulting from consumption over the period of adolescent development and growth.
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INTRODUCTION |
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METHOD |
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Measures
Demographic measures
Demographic characteristics were measured using a series of closed
questions. The nine categories recommended by the Government Statistical
Service (1996) were used to
assess ethnicity. Because of the small numbers of respondents in most of the
non-White ethnic groups, the categories were collapsed into five groups
(White, Black, Indian,
Pakistani/Bangladeshi and other) as used by
Meltzer et al (2000).
The addresses of participating families were classified using six broad
categories from the ACORN geodemographic targeting classification
(CACI Information Services,
1993). These categories provide a broad socio-economic
categorisation which is complementary to social class categorisation.
Family variables
The parent interviews included questions about the characteristics of the
family in which the child was living. These included the marital status of the
parent (married, cohabiting or lone parent), the number of children in the
household, family economic status (whether either or both parents were
working) and gross annual household income (a series of categories which were
later used to calculate weekly income). The parent was also questioned about
the type of accommodation in which the family lived (detached, semi-detached
or terraced house, maisonette or flat) and housing tenure (whether the
property was owned, or rented privately or from the social sector). The
reported relationships between different family members in the household were
recorded to establish whether or not the family was
reconstituted (i.e. if there were any stepchildren in the
family).
Mental health
Mental health was assessed using items based on ICD10 and
DSMIV diagnostic criteria (World
Health Organization, 1992; American Psychiatric Association,
1994). Structured interviews tend to elicit overreporting of rare
symptoms. It has been suggested that this might arise from respondents not
fully understanding the questions (Brugha
et al, 1999). To address this problem, the structured
questions were supplemented by open-ended questions which interviewers were
instructed to use when symptoms were identified. Answers to these questions
were transcribed but not rated by the interviewers. Instead, experienced
clinical raters, masked to the data on substance use, reviewed the data from
the structured and open-ended questions and assigned each child a diagnosis
(or no diagnosis). Further details of these measures and of the validity and
reliability of the resulting diagnoses have been published elsewhere
(Goodman et al,
2000).
Psychoactive substance use
Questions pertaining to the use of alcohol, cigarettes and cannabis were
taken from the national surveys of smoking, drinking and drug use conducted by
the ONS (Goddard & Higgins,
1999; Becher et al,
2001). These were self-completed using a laptop computer.
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RESULTS |
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Mental health
Just over one in ten of the children in this study were classified as
having a psychiatric diagnosis. Of these, 171 children had an emotional
disorder, of whom 66 were diagnosed with a depressive disorder. The remaining
136 children had other disorders (predominantly disruptive behavioural
disorders, but ranging from pervasive developmental disorder to eating
disorders). The numbers with specific diagnoses were too small for meaningful
analysis and so broad categories for type of disorder were used.
Drinking, smoking and cannabis use
One hundred and sixty-six of the respondents indicated that they did not
wish to complete the section of the interview pertaining to substance use.
These cases were therefore dropped from the analyses using these variables,
leaving data on 2458 remaining cases. There was no significant demographic
difference between the study participants who responded to the questions on
substance use and those who did not.
A third of the responders (867; 35.3%) reported that they had never consumed an alcoholic drink. A further 35 (1.4%) stated that they did not currently drink alcohol. Of the 1557 drinkers, 286 (18.4%) estimated that they drank alcohol at least once a week and were classified as regular drinkers. Half of the participants claimed that they had never tried a cigarette, and a further quarter that they had smoked just once; 189 indicated that they used to smoke and 113 that they currently smoked occasionally. Just 9.0% (222) of the sample classed themselves as regular smokers and just over half of these (56.1%) were girls.
Almost one in ten (216; 8.8%) admitted to having tried cannabis (88 girls), 91 of whom estimated that they were using this drug at least once a month at the time of interview.
An eight-category polysubstance use variable was computed to show the three-way cross-over between those classified as regular smokers, regular drinkers and lifetime cannabis users. Four-fifths of the sample (1964; 79.9%) were not current drinkers or smokers and had never used cannabis. These were assigned a score of 0 to denote the baseline comparison category. A further 81 participants (3.3%) were classified as regular smokers only; 162 (6.6%) were regular drinkers only; 77 (3.2%) had used cannabis only; 36 (1.5%) were both regular drinkers and smokers; 51 (2.1%) were regular smokers who had also used cannabis; 35 (1.4%) were regular drinkers who had also used cannabis; and finally, 53 (2.1%) were both regular smokers and drinkers and had also used cannabis.
Logistic regression analyses
Three series of logistic regressions were conducted to explore the
characteristics of the regular smokers, the regular drinkers, and the lifetime
cannabis users. Respondents were characterised in terms of demographic data,
family background variables, psychiatric diagnoses and other substance use.
Frequency data for these variables are presented in
Table 1.
Table 2 summarises the results
from the logistic regression analyses showing the adjusted odds for the
predictor variables that reached statistical significance
(P<0.05).
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Demographic variables
As expected, increased age was a significant risk factor for use of all
three substances: the odds for regular smoking and regular drinking at age 15
years were almost triple those for 13-year-olds. Gender was a significant
predictor in just two of the models: female respondents were less likely to be
regular drinkers or to have used cannabis than their male peers. Black and
Indian children were less likely to be current smokers than those who were
White. Ethnic group did not predict regular alcohol use or cannabis use in the
other two models.
Family variables
There was little consistency in which family variables were associated with
substance use in the sample. Children who were living in families where there
were stepchildren were more than twice as likely to be regular smokers. A
similarly increased risk was associated with living in social-sector rented
accommodation. In contrast, children from families where just one parent was
working were less than half as likely to be current smokers than those with
two working parents. Similarly, greater household income was also associated
with a reduction in smoking risk.
Respondents who were classified as living in a thriving area according to the ACORN categories were more likely to be regular drinkers than those from any of the other five categories. Living in social-sector rented accommodation decreased the risk of regular alcohol use.
Just one family variable reached significance in the model predicting lifetime cannabis use: children from lone parent families were almost twice as likely to have used cannabis than children from families where the parents were married (adjusted OR=1.85, P<0.01).
Mental health
Each of the three categories of psychiatric disorder was associated with an
increased risk of being a regular smoker. In particular, those suffering from
a depressive disorder were over five times as likely to be smokers. Depressive
disorder also doubled the risk of regular drinking (adjusted OR=1.97,
P<0.05) and of lifetime cannabis use (adjusted OR=2.37,
P<0.05). The odds for cannabis use by those with some other
non-emotional type of disorder were similarly inflated (adjusted
OR=1.96, P<0.05).
Psychoactive substance use
Smoking, drinking and cannabis use were consistently interrelated, with
more frequent use of one substance carrying an increased risk of use of the
other two. For example, when compared with non-drinkers, respondents who
reported that they drank alcohol at least once a fortnight were almost five
times as likely to be regular smokers. The odds ratio increased to 8.28 in
respondents who drank at least once a week. Furthermore, the likelihood of
being classified as a regular drinker was approximately double in adolescents
who had tried cigarettes and eight times greater in regular smokers. Similar
relationships were observed between cannabis use and regular smoking and
drinking. When compared with non-cannabis users, respondents who admitted to
using this drug at least once a month at the time of interview were 11.44
times more likely to be regular smokers and 2.67 times more likely to be
regular drinkers.
Relationship between substance use and mental health
The relationship between substance use and mental health was examined
further by means of four additional logistic regressions with the following
dependent variables:
The relationship between the eight-category polysubstance use variable described earlier and psychiatric diagnoses was examined while controlling for the background and family variables in Table 2. The results from these four regressions are presented in Table 3. Individuals who were not classified as regular drinkers or smokers and had never used cannabis were used as the comparison group (labelled none).
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Any diagnosis
The likelihood of having any psychiatric diagnosis was quadrupled in
adolescents who were just regular smokers. A similarly increased risk was
evident in those who were regular smokers and regular drinkers. Furthermore,
regular smokers who had also used cannabis were almost seven times as likely
as those in the none category to have a psychiatric disorder,
and the risk doubled again (adjusted OR=14.17, P<0.001) for users
of all three substances.
Depressive diagnosis
Both the regular smokers and the regular drinkers who had also used
cannabis were four to five times more likely to have a depressive disorder
than those in the comparison category. For those who both smoked and drank on
a regular basis, the adjusted odds ratio increased to 7.11
(P<0.01). However, by far the greatest risk for a depressive
disorder was observed in the users of all three substances (adjusted OR=26.80,
P<0.001).
Other emotional disorder
The relationship between substance use and other emotional disorders was
less pronounced. In common with the other diagnoses, being a regular smoker
was associated with an increased risk (adjusted OR=2.86, P<0.01),
as was being a user of all three substances (adjusted OR=2.55,
P<0.05).
Other psychiatric disorders
Once again, participants who reported regular smoking were over five times
more likely to have a diagnosis of other (non-emotional) psychiatric
disorder; these odds increased to 6.92 for regular users of both
tobacco and alcohol and to 8.77 for regular smokers who had tried cannabis.
Finally, the increase in risk for users of all three substances was 7.31
(P<0.001).
Interactions between substances
Further analyses were conducted to examine which of the three substances
(tobacco, alcohol and cannabis) predicted each of the above four categories of
psychiatric disorder. A series of logistic regressions examined the
relationship between psychiatric diagnosis and the interactions between the
three substances. These showed that the main drug-related effects were
primarily due to whether or not individuals were categorised as regular
smokers, and secondarily whether or not they were regular cannabis users (with
one exception: only regular smoking predicted other emotional
disorder; adjusted OR=2.13, P<0.01). In particular, in
respondents who smoked, the risk of having any type of psychiatric diagnosis
was more than quadrupled (adjusted OR=4.35, P<0.001); the odds
were 3.45 for depressive disorders (P<0.001), 2.13 for other
emotional disorders (P<0.004) and 4.66 for other types of
psychiatric disorder (P<0.001). Regular use of cannabis (more than
once a month) further increased the risk of any psychiatric diagnosis by a
factor of 3.50 (P<0.001), that of depressive disorder by 3.91
(P<0.001) and that of other psychiatric diagnosis by 2.18
(P<0.05). In no case was there any additional effect associated
with having used cannabis on a less frequent basis, regular alcohol use or
taking all three substances that could not be explained by other drug
combinations.
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DISCUSSION |
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In the initial logistic regression analyses, regular smoking was consistently related to the psychiatric disorders studied. In particular, those with depressive disorders were over five times more likely to be regular smokers than individuals with no diagnosis. Other research studies have noted similar links between smoking and affective disorders in both adults (e.g. Glassman et al, 1990; Farrell et al, 2001) and young people (Breslau et al, 1991; Patton et al, 1996; Fergusson & Woodward, 2002). Associations between tobacco use and drug dependence, anxiety and psychosis have also been reported elsewhere (Degenhardt & Hall, 2001). One study found strong links between nicotine dependence and nearly all psychiatric disorders in adolescents, yet no consistent relationship between disorders and regular smoking or experimental use (Dierker et al, 2001). In our study no distinction was made between regular and dependent nicotine use; dependent individuals were included in the general category labelled regular smokers. Consequently, it is possible that the strong relationships between psychiatric diagnoses and regular use noted here were in fact driven by the presence of nicotine-dependent individuals in this category.
The finding that depressive disorders and other (non-emotional) psychiatric disorders were associated with roughly double the risk of cannabis use is consistent with studies that have noted that people who use cannabis are at greater risk of psycho-social disorders and personal adjustment problems than those who do not (e.g. Reilly et al, 1998; Troisi et al, 1998). Regier et al (1990) found that half of the cannabis-dependent individuals from a community sample met DSMIII criteria (American Psychiatric Association, 1980) for other disorders (excluding alcohol- or drug-related disorders). Similar findings have been described in adolescents and young people (e.g. Rey et al, 2002). Fergusson et al (1997) reported an association between early cannabis use (before the age of 15 years) and an increased risk of a range of psychiatric disorders and problem behaviours.
Polydrug use
It is widely recognised that many adolescents who engage in the regular use
of one psychoactive substance are also users of other licit or illicit drugs.
This presents a considerable challenge when attempting to ascertain which
particular drug or drug combinations are associated with psychiatric
morbidity. Kandel and colleagues examined the comorbidity of dependence on
single and multiple drugs with anxiety and depressive disorders, and found
that for individuals who were uniquely dependent on cigarettes, alcohol or
illicit drugs the risk of psychiatric diagnosis was roughly doubled, while
being dependent on an illicit drug and a legal substance quadrupled this risk
(Kandel et al,
2001).
We approached this problem by examining the relationship between mental health and different categories of substance in the sample (regular smoking, regular drinking and cannabis use, and the four possible combinations of these behaviours), while controlling for background and socio-familial factors. The regular smokers, and respondents who were in the category for all three drugs, were consistently at greater risk of psychiatric disorders. Furthermore, if a regular smoker was also a regular drinker or had used cannabis, the risk of mental disorder was further increased (with one exception: other emotional disorder). Second, the analyses examined which of the three types of substance use (tobacco, alcohol and cannabis) was most closely related to psychiatric diagnoses. The strongest effect was associated with regular cigarette smoking, with an additional risk if an individual was a regular cannabis user (again, with one exception: other emotional disorder). Less frequent cannabis use and regular alcohol use were both unrelated to psychiatric disorder when background variables and other substance use were controlled for. These results complement those reported by Degenhardt et al (2001), who found consistent links between tobacco use and a number of different psychiatric diagnoses in a representative sample of Australian adults. Another study found stronger links between psychopathology and extent of cannabis use compared with alcohol use (Milich et al, 2000). However, it is worth noting that although the current study provided little evidence for links between regular alcohol use and psychiatric disorders, follow-up data would be required to examine whether long-term regular use of alcohol is linked to subsequent negative psychiatric outcomes.
Socio-demographic findings
A number of socio-demographic factors were associated with smoking,
drinking and cannabis use over and above the influence exerted by psychiatric
disorders and other substance use. Female participants were less likely to be
regular drinkers or to have ever used cannabis than their male peers.
Interestingly, despite evidence from other recent UK-based studies that girls
are more likely to be regular smokers than boys of a similar age (e.g.
Becher et al, 2001), gender was not significantly related to regular smoking in the current
analyses. In common with the results of the majority of national and
international studies of substance use in adolescence (e.g.
Becher et al, 2001;
Rey et al, 2002)
smoking, drinking and cannabis use were found to be strongly associated with
increasing age.
Children from more affluent families were slightly more likely to be regular alcohol users, but less likely to smoke cigarettes regularly. Although seemingly unrelated to smoking or cannabis use, the ACORN categories (CACI Information Services, 1993) predicted regular alcohol use: respondents from families living in thriving areas (those populated by wealthy achievers living in suburban areas, affluent greys (middle-aged people) in rural communities and prosperous pensioners in retirement areas) were significantly more likely to be regular drinkers than those from elsewhere. It is possible that the consumption of alcohol under parental supervision at mealtimes was more common among the more affluent families. This could explain the higher prevalence of weekly drinking in children from families with higher incomes, families who are owner-occupiers and those who live in thriving areas. In contrast, it is unlikely that the cigarette and cannabis use occurs to a similar degree in what could be described as positive family contexts. Future studies that explore the links between substance use and psychiatric morbidity should control for the social context of substance use (particularly alcohol) so that the relationships noted in the current study can be further disentangled.
In contrast, respondents living in social-sector rented accommodation were less likely to be regular drinkers, but approximately twice as likely to be regular smokers compared with those living in privately owned homes. The likelihood of being a regular smoker decreased significantly with increasing gross household income. A strong association between deprivation and levels of smoking has been noted by a number of researchers (e.g. Jarvis & Wardle, 1999). Our findings indicate a similar relationship for tobacco.
Relationships between substance use and family structure were also evident. Children from what were classified as reconstituted homes (i.e. with stepchildren) were more than twice as likely to be regular smokers. In contrast, the smoking risk for participants who came from homes where just one parent was working was less than half of that for respondents with two working parents. Finally, in common with findings noted by Rey et al (2002) from a sample of Australian teenagers, children of lone parents were nearly twice as likely than their peers to have tried cannabis.
Limitations of the study
A number of limitations should be considered when interpreting the findings
from this study. First, the measures pertaining to substance use relied solely
on self-report. Although reviews have suggested that this is a reasonably
accurate means of eliciting data on this subject from young people, the
quality of the data is likely to be affected by the circumstances under which
interviews were conducted. The levels of self-reported substance use tended to
be lower than those from other recent UK national surveys such as those by
Becher et al (2001)
and by Goddard & Higgins
(1999). Although considerable
effort was invested in emphasising the confidentiality of the data, the fact
that interviews were conducted in a home setting and respondents were aware
that their parents and a schoolteacher were also going to be interviewed for
the study might have contributed to more underreporting of substance use than
studies that have used self-completion techniques to gather data within the
school environment. Furthermore, it is possible that the 166 participants who
opted out of the section on substance use did so because they were in fact
substance users. This paper therefore implicitly assumes that no bias was
engendered by this potential underreporting. Because of the broad nature of
the core aims of the survey the actual questions on substance use were limited
and no measures of dependence were taken. A further limitation was that the
small numbers of individuals with particular diagnoses precluded more specific
analyses to examine differences in the links between substance use and
individual disorders.
In summary, the study has provided additional evidence that users of one substance are at increased risk of using others. The findings also confirm previous assertions that substance use and psychiatric disorders often co-occur in adolescents as well as in adults. Finally, analyses of the interactions between smoking, drinking and cannabis use indicated that the primary link between substance use and psychiatric disorder was explained by regular smoking, and that the risk of disorder was additionally augmented if an individual was using cannabis on a regular basis.
Clinical implications
It has been noted elsewhere that a large proportion of research into
psychiatric morbidity and substance use has tended to focus on alcohol and
illicit drug use, with smoking as a secondary interest
(Dierker et al,
2001). Our findings suggest that far from being subsidiary,
tobacco use is of central importance when trying to make sense of the links
between substance use and mental disorders. There is growing interest in the
links between smoking and psychiatric disorders. The current findings provide
further evidence that smoking is linked to baseline psychiatric morbidity and
to other forms of substance involvement too. It is important not to overlook
both legal and illegal substance use issues in adolescents who are showing
signs of psychiatric problems. Similarly, where substance use concerns are
brought to the fore, it could be useful to screen for and address psychiatric
morbidities. Finally, our results emphasise the importance of investing in
smoking prevention at an early age.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication September 18, 2002. Revision received January 17, 2003. Accepted for publication January 20, 2003.
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