National Addiction Centre, Institute of Psychiatry, King's College London
Department of Psychiatry and Behavioural Science, Royal Free and University College London Medical School
Department of Psychiatry, University of Leicester
Institute of Psychiatry, King's College London
Department of Psychological Medicine, University of Wales College of Medicine
National Addiction Centre, Institute of Psychiatry, King's College London
Office for National Statistics, London
Correspondence: Dr Michael Farrell, Senior Lecturer and Consultant Psychiatrist, National Addiction Centre, Institute of Psychiatry and Maudsley Hospital, 4 Windsor Walk, London SE5 8AF, UK. E-mail: m.farrell{at}iop.kcl.ac.uk
Declaration of interest None. Funding detailed in Acknowledgements.
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ABSTRACT |
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Aims This study aims to report on consumption patterns of and dependence on nicotine, alcohol and non-prescribed drugs and to report on the levels of psychiatric morbidity in these groups.
Method A national household study of psychiatric morbidity was conducted in England and Wales. Psychiatric assessment was based on the Clinical Interview Schedule Revised (CISR). Measures of nicotine, alcohol and drug use and dependence were obtained. This paper compares the levels of psychiatric morbidity in the non-dependent and the nicotine-, alcohol- and drug-dependent cases.
Results Twelve per cent of the non-dependent population were assessed as having any psychiatric disorder compared with 22% of the nicotine-dependent, 30% of the alcohol-dependent and 45% of the drug-dependent population.
Conclusions There is a clear relationship between dependence on nicotine, alcohol and drugs and other psychiatric morbidity.
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INTRODUCTION |
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Having one psychiatric disorder significantly increases the risk of having multiple psychiatric disorders (Kessler et al, 1997). The relationship between psychiatric disorders, substance consumption, misuse and dependence has been the subject of a large-scale epidemiological study (Helzer & Pryzbeck, 1988; Regier et al, 1990; Robins & Regier, 1991; Kessler et al, 1994). The issue of comorbidity of substance use disorders and other psychiatric disorders has become a major policy issue (Hall & Farrell, 1997). The British Psychiatric Morbidity Survey is the largest programme of epidemiological research on the prevalence of psychiatric disorders conducted to date in the UK (Meltzer et al, 1995; Jenkins et al, 1997a,b). The comparison of the prevalence of nicotine, alcohol and drug dependence across prison, homeless and institutional populations is reported elsewhere (Farrell et al, 1998).
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METHOD |
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Measures of psychiatric morbidity
The Clinical Interview Schedule Revised (CISR;
Lewis et al, 1992)
was used to measure levels of psychological morbidity. The Office of
Population Censuses and Surveys (OPCS; now named the Office for National
Statistics) questions on tobacco and alcohol consumption used regularly in
national surveys were included. Added to were measures of alcohol problems
used in the US National Alcohol Survey
(Hilton & Clark, 1991), which recorded experiences over the past 12 months. The Diagnostic Interview
Schedule (DIS) on non-prescribed drugs
(Robins et al, 1981)
was adopted as the measure of use of non-prescribed drugs and dependence.
Measures for nicotine, alcohol and other drugs met ICD10
(World Health Organization,
1992) criteria for dependence. The criteria for alcohol dependence
required three or more dependence symptoms and were consistent with the
criteria for an ICD10 diagnosis of alcohol dependence. Parallel surveys
were conducted on an institutional
(Meltzer et al, 1996) and homeless sample (Gill et al,
1996) and also on a prison sample
(Singleton et al,
1999). A repeat household survey is currently under way. Logistic
regression was conducted to examine the relationship between consumption and
dependence on alcohol, nicotine and non-prescribed drugs and psychological
morbidity. Psychological morbidity was measured using CISR scores, with
those scoring above 12 classed as suffering from mixed anxiety and depressive
disorder (F41.2). The use of algorithms allowed the ICD10 diagnosis of
anxiety and depressive disorders from the CISR.
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RESULTS |
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Overall, 5% of those interviewed were classed as alcohol dependent. Alcohol
dependence varied according to age, gender and consumption levels
(Table 1). With regard to
gender, 8% of men and 2% of women were classified as alcohol dependent. The
pattern of drinking was categorised as: light drinkers, 1-7 units/week for
women and 1-10 units per week for men; moderate drinkers, 8-14 units/week for
women and 11-21 units/week for men; heavy drinkers, 15+ units/week for women
and 22+ units/week for men (this category subdivided into fairly heavy (15-25
units/week for women and 22-35 units/week for men), heavy (26-35 units/week
for women and 36-50 units/week for men) and very heavy drinkers (36
units/week for women and
51 units/week for men)). Alcohol dependence
increased according to consumption levels, rising from 4% dependent among
moderate drinkers to 34% among the heavy drinkers. Alcohol dependence was most
common among the younger age group of 16-24 years.
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Drug use and dependence
Five per cent of all adults interviewed reported having taken an illegal
drug. Cannabis was the most commonly used drug (5%), followed by stimulants
(1%) and hallucinogens (1%). Rates of heroin, cocaine and amphetamine use were
insufficient to allow separate analyses. For the purposes of these analyses,
drug types were divided into two groups: the use of cannabis and the use of
other drugs, which include stimulants, hallucinogens, hypnotics, opiates and
solvents. Subjects may have taken more than one type of drug.
As with alcohol consumption, drug use varied according to age and gender
(Table 2). Men were
significantly more likely to have used an illegal or non-prescribed drug in
the past (7% compared with 4%) (2=42.30, d.f.=1,
P<0.0001), and the use of drugs was far more common among the
youngest age group and declined rapidly with increasing age. For example, 15%
of adults in the age group 16-24 years had used a drug in the past year,
compared with only 6% of those aged 25-34 years and only 1% of those aged
45-55 years.
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Similarly, drug dependence varied according to age and gender, with 6.7% of those aged 16-24 years scoring as dependent compared with 0.5% of those aged 55-64 years. Men were more likely to score as dependent, with 2.8% of men classed as drug dependent compared with 1.5% of women. Dependence also varied according to drug type, with 1.8% classed as dependent on cannabis and 1.2% classed as dependent on other drugs (Table 2).
Tobacco consumption and nicotine dependence
At the time of interview 32% of those surveyed were current smokers, with
8% classed as light smokers (less than 10 a day), 13% moderate smokers (10-20
a day) and 11% heavy smokers (more than 20 a day). At interview, two-thirds of
the sample did not smoke cigarettes, with 47% having never smoked cigarettes
and 22% classed as ex-smokers. Unlike alcohol and tobacco consumption, among
those who smoked there were no gender differences in patterns of cigarette
consumption (Table 3). However,
women were significantly more likely to have never smoked cigarettes
(2=79.02, d.f.=1, P<0.0001) and men were
significantly more likely to be ex-smokers and have quit smoking at some point
in the past (
2=70.77, d.f.=1, P<0.0001). Patterns
of cigarette consumption did vary according to age, with the heaviest smoking
being most common among men and women aged 25-55 years.
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Regarding dependence on nicotine, anyone who currently smoked cigarettes was classed as dependent, that is, 32% of the sample (50% male and 50% female). Measures are available to discern the severity of nicotine dependence but this is not explored further here.
Psychiatric morbidity
A total of 15.5% of all subjects were scored as having a psychiatric
disorder, with 13.5% having one disorder and 2% of subjects having two or more
disorders. Women were more likely than men to have a disorder, with 17% of
females having one disorder compared with 10% of men and 2.6% of females
having two or more disorders compared with 1.5% of men.
Drug, alcohol and nicotine dependence and the increased risk of
psychiatric morbidity
The relationship of drug, alcohol and nicotine dependence to psychological
morbidity was explored across the sample
(Table 4). The non-dependent
population (i.e. those who were scored as non-dependent on drugs, alcohol and
nicotine) were compared with those who were classed as drug, alcohol or
nicotine dependent: 67% (6779) of the total sample were classed as
non-dependent, whereas 33% (3329) were classed as drug, alcohol or nicotine
dependent, with nicotine dependence accounting for the majority of this.
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There was a clear relationship between dependence on nicotine, alcohol and drugs and psychological morbidity. The non-dependent population differed significantly in terms of the presence of disorders from the drug-, alcohol- and nicotine-dependent population: 12% of the non-dependent population were assessed as having any disorder compared with 22% of the nicotine-dependent, 30% of the alcohol-dependent and 45% of the drug-dependent population. Significant differences across the groups also were found for the presence of two or more disorders: the highest prevalence rates were among the drug-dependent population, where 12% were assessed as having two or more disorders, compared with only 1% of the non-dependent population.
Given that there are significant social and demographic factors associated with drug, alcohol and nicotine dependence and with the presence of psychiatric disorders, a multiple logistic regression was performed to control for these and for other significant factors that may confound the observed association between drug, alcohol and nicotine dependence and psychiatric disorder. The odds ratios (ORs) produced show the increase or decrease in the odds of having a psychiatric disorder that an individual with a particular characteristic had in relation to those in a reference category (for which the OR is 1.00) while taking into account the possible confounding effects of other factors in the model.
The following variables were entered into a regression model where having a disorder v. having no other psychiatric disorder was the dependent variable: drug dependence, alcohol dependence, nicotine dependence, age, gender, ethnicity, employment status, marital status, housing tenure and family unit type.
Table 5 shows that dependence on drugs, alcohol or nicotine was associated significantly and independently with having a psychiatric disorder, even after various social and demographic characteristics were controlled for. A respondent's age, gender, marital status, housing tenure, work status, type of work (manual v. non-manual) and dependence on drugs, alcohol and nicotine all were found to be associated independently with having a disorder. However, the dependence variables showed the strongest association with having a psychiatric disorder. Analyses showed that a drug-dependent subject was about three times more likely to have a disorder compared with a non-drug-dependent subject (OR=3.25). Alcohol dependence also was associated with increased odds of having a disorder (OR=2.20), as was nicotine dependence (smoking cigarettes, OR=1.60).
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The relationship between drug, alcohol and nicotine dependence and psychiatric disorder was found to hold true according to the type of disorder experienced (Table 6). For mixed anxiety disorders, generalised anxiety disorders, depression and phobic and panic disorders there was a clear association between dependence and non-dependence. Across all categories of disorder the prevalence of disorders differed significantly between the non-dependent and the drug-, alcohol- and nicotine-dependent populations, with the highest rates of disorder generally reported among the drug-dependent group.
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Gender differences
Significant gender differences were found in the prevalence of psychiatric
disorders across all groups except in the drug-dependent population. Females
in the non-dependent, nicotine-dependent and alcohol-dependent populations
were significantly more likely than males to report the presence of a
psychiatric disorder. Among the drug-dependent population, gender differences
in psychological morbidity disappear males and females were equally
likely to score as having a disorder. Among subjects scoring positively for
two or more disorders in the non-dependent population, females were
significantly more likely to report two or more disorders. However, among the
nicotine-, alcohol- and drug-dependent populations no gender differences were
found in the prevalence of two or more disorders.
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DISCUSSION |
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Nature of the relationship between dependence and psychiatric
morbidity
This study shows excess morbidity, with the greatest excess in those who
are drug dependent, a stepwise reduction to alcohol and a further reduction
for nicotine dependence. There does not appear to be any consensus about the
nature of the relationship but a bi-directional model appears to be the most
plausible. Currently, premorbid psychological or developmental vulnerability
is well described as being associated with early involvement with illicit drug
use and similar characteristics are associated with early initiation of
nicotine and alcohol consumption. Cumulative comorbidity across these
substances also is likely to add to the gradient, with high rates of nicotine
and alcohol dependence in the drug-dependent population.
There is much interest in the self-medication hypothesis for the use of a range of psychoactive substances but little empirical data to support such a hypothesis, except possibly for the case of affect regulation and consumption of nicotine (Cooney et al, 1998).
Kessler (1995) reports that affective disorders and anxiety disorders are strongly comorbid and that disorders of a single type are more strongly related to each other than to disorders of another type. Kessler et al (1997) report that the relationship of mood and anxiety disorders with substance use disorders was among the weakest comorbidities. Currently, there is a strong appreciation that there are many complex factors influencing the relationship of different disorders.
Studies that could examine directly the nature of the relationship between substance consumption and psychiatric morbidity ideally require a large population cohort followed from early teens into adulthood so that risk factors and measures of personality and psychological well-being prior to involvement with tobacco, alcohol or other drugs could be measured and longitudinal follow-up might determine the contribution of quantified tobacco, alcohol and other drug consumption and dependence to the evolution of psychiatric morbidity.
Such studies are not currently available, but cross-sectional studies provide some indication of the nature of the relationship. Apart from drug-induced organic psychosis, there are very few conditions that are robustly linked to a specific substance. Most of the reports indicate increased levels of disorders across the whole spectrum of disorders. Some studies have reported increased rates of phobic, agoraphobic and panic disorders in alcoholics (Stockwell et al, 1984) but the larger population-derived samples do not support this (Kessler et al, 1997). Probably, the most robust association is for bipolar disorder, the presence of which seems to be related clearly to increased rates of alcohol dependence in men.
Generalised increase in psychiatric disorder
The non-specific nature of the increase in the disorders would lead one to
hypothesise that much, if not all, of the disorder is related to quantity and
frequency of consumption of substances that can give rise to anxiety,
dysphoria and related subjective feelings. Some of the clinical studies
indicate that complete cessation of substance consumption can be associated
with immediate improvement in measures of psychological well-being
(Raimo & Schukit, 1998). However, abstinent alcohol-and drug-dependent individuals score higher on
measures of anxiety and mood-related disorders than the general population.
Such a finding is consistent with raised baseline measures of psychiatric
morbidity of at-risk young people but also with the longer term impact of
prolonged nicotine, alcohol and drug consumption.
Limitations of the study
The low prevalence of psychotic disorder and other major mental illness
makes analyses and reporting on this type of psychiatric comorbidity
difficult. Comorbidity with severe mental illness is a topic of major policy
concern and some of the issues need to be clarified in studies of
non-treatment populations (Johnson,
1997).
This current study is a large British cross-sectional study that reports elevated rates of non-psychotic disorders, with increasing levels of disorders associated with increasing levels of engagement with tobacco, alcohol and other drugs. Future studies with detailed measures of the severity of alcohol and drug dependence would help to elucidate the nature of the relationship between the severity of dependence and the degree and severity of psychiatric disorder. This survey measures Axis I disorders and it is likely that Axis II disorders are linked more strongly with alcohol and drug dependence, both for premorbid risk of involvement and as predictors of the severity of dependence. Axis II disorders have been measured in the repeat survey.
Overall, this cross-sectional study replicates other international studies and demonstrates a strong association between nicotine, alcohol and drug dependence, but the nature of the relationship requires longitudinal studies if it is to be elucidated further.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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REFERENCES |
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Received for publication September 20, 2000. Revision received May 10, 2001. Accepted for publication May 17, 2001.
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