St Charles' Hospital, London, UK
Cognitive Neuropsychiatry Research & Academic Unit. The University of Melbourne and Sunshine Hospital, Melbourne, Australia
Brent, Kensington, Chelsea and Westminster Substance Misuse Service, London, UK
Division of Neuroscience and Psychological Medicine, Imperial College School of Medicine, London, UK
Correspondence: Professor Thomas R. E. Barnes, Imperial College School of Medicine, Academic Centre, Ealing Hospital, St Bernard's Wing, Ealing, Middlesex UBI 3EU, UK
Declaration of interest Grant from North Thames Regional Health Authority.
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ABSTRACT |
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Aims To study the extent and nature of comorbid non-alcohol substance misuse in people with schizophrenia in central London.
Method Subjects were identified in an epidemiological census survey of South Westminster. Standardised assessment of each subject included demographic data, ratings of mental state and movement disorder and questioning about drug and alcohol misuse.
Results Individuals with schizophrenia or related psychoses were identified (n=352) and 57 (16%) reported a lifetime history of non-alcohol substance misuse. Age and gender were the main variables relevant to the extent and pattern of misuse. Self-reported non-alcohol substance misuse showed no significant relationship with a range of outcome measures.
Conclusions The high proportion of subjects reporting non-alcohol substance misuse is comparable with figures from the USA. The reports of lifetime misuse most commonly referred to cannabis, psychostimulants, LSD, opiates and anticholinergics. Misuse was concentrated in those younger than 36 years and was reported more often by males.
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INTRODUCTION |
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METHOD |
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Questionnaire and interview schedules
A detailed questionnaire and case-note review provided demographic data,
history of onset and course of illness, and ICD-9
(World Health Organization,
1978) and Feighner criteria for schizophrenia
(Feighner et al,
1972). Substance misuse was assessed using the Substance Use
Rating Scale, patient version (SURSp; Duke
et al, 1994). The SURSp contains ten questions derived
from the Severity of Alcohol Dependence Questionnaire
(Stockwell et al,
1983). It elicits information about the use of legal drugs such as
nicotine and caffeine, before proceeding to detailed questioning about the
onset of use, maximum ever use and current use of illicit drugs. Direct
questions are asked about the use of cannabis, opiates, sedatives, stimulants
such as cocaine, crack cocaine, amphetamines and ecstasy, and hallucinogens.
Mental state was assessed using the Manchester Scale
(Krawiecka et al,
1977). Movement disorders were assessed using the Tardive
Dyskinesia Scale (TDS; Barnes & Trauer,
1982), the Abnormal Involuntary Movement Scale (AIMS;
Guy, 1976), the modified
Extrapyramidal Side-Effects Rating Scale (EPSE;
Simpson & Angus, 1970) and
the Barnes Akathisia Rating Scale (BARS;
Barnes, 1989).
Statistical analysis
The data were analysed using SPSS, version 9.0 (SPSS Inc, Chicago, IL).
Between sub-groups, comparisons were made using the 2 test or
Fisher's exact test. All probabilities quoted for t-tests are
two-tailed.
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RESULTS |
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Diagnosis
Of the total sample, including 49 patients (14%) in long-stay psychiatric
hospitals, 223 (63%) had received a primary diagnosis of schizophrenia
according to ICD-9. Only 142 (40%) fulfilled the Feighner criteria for
definite schizophrenia.
Rates of non-alcohol substance misuse on self-report
Overall, 57 patients gave a lifetime history of misuse of substances other
than alcohol. This was 21.5% of the 265 patients for whom adequate information
was available. There was no significant statistical association between
self-report of non-alcohol substance misuse and a diagnosis of schizophrenia
by Feighner criteria as opposed to other diagnoses made according to ICD-9.
The frequencies of reported lifetime non-alcohol substance misuse are shown in
Table 2. Almost all patients
admitting to past non-alcohol substance misuse had tried more than one of the
listed substances. Only 13 patients admitted to current non-alcohol substance
misuse, that is, illicit use of a drug in the previous month. In 12 cases this
was cannabis misuse and in one case benzodiazepine misuse. No further
statistical analysis was judged appropriate for this small number of patients.
The remainder of the analysis refers to lifetime self-reported history of
non-alcohol substance misuse, defined by a clear statement on questioning that
a substance had knowingly been taken for a non-medical purpose.
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Age
Having a lifetime history of non-alcohol substance misuse on self-report
was significantly associated with being less than 36 years of age. For those
completing the substance misuse questionnaire, 57% of those aged 35 years or
younger admitted to non-alcohol substance misuse, compared with 9% of those
over 35 years (Pearson's 2=65.437, 1 d.f.,
P<0.0001). The only drugs misused with anything approaching the
same frequency in the older age group as in the younger were the
anticholinergics (7% of those over 35 years and 10% of those aged 35 or
under). The remainder of the analysis focuses on those aged 35 years or
younger at assessment and for whom detailed drug histories were available (67
out of 82 patients; 82% of those aged 35 years or less).
Gender and ethnic origin
Ethnic origin was determined by self-report. The most common ethnic groups
were White (61%) and African-Caribbean and Black African (31%). Asian and
other ethnic groups accounted for only 1.5% and 3% of the total sample,
respectively. Data were missing on two subjects (3%). However, the numbers of
individuals from each ethnic grouping were considered too small to permit a
meaningful statistical analysis of the relationship between ethnic origin and
self-report of lifetime non-alcohol substance misuse. When all ethnic groups
were considered together, men (64%) were more likely than women (41%) to
report lifetime non-alcohol substance misuse (Pearson's
2=11.47, 1 d.f., P=0.001).
Table 2 shows that, in descending order of frequency, subjects reported lifetime misuse of cannabis, psychostimulants, LSD (lysergic acid diethylamide), opiates, anticholinergics, sedatives, ecstasy, PCP (polychlorophenol) and solvents. This rank order was preserved across different age groups and between genders, with minor variations. In the under-35-year age group, women reported lower rates of cannabis misuse than men. Women were slightly less likely to report anticholinergic misuse and slightly more likely to report misuse of benzodiazepines. The small numbers of female subjects reporting any substance misuse prohibited adequate statistical comparison for these substances.
Relationship between non-alcohol substance misuse, age of onset of
illness and outcome variables
Just under half (48%) had misused substances other than alcohol before
their first psychiatric presentation. Only 18 out of 34 in current contact
with psychiatric staff reported disclosing their non-alcohol substance misuse.
No significant association was found between giving a history of lifetime
non-alcohol substance misuse and age of onset of illness (defined as age of
first contact with health professionals because of psychiatric symptoms).
Further, no association was found between reported lifetime history of
non-alcohol substance misuse and number of admissions to hospital, number of
compulsory admissions, accommodation in temporary housing, employment status
or marital status.
Relationship between non-alcohol substance misuse, psychiatric
symptoms and movement disorders
No significant association was found between reporting a history of
lifetime non-alcohol substance misuse and the presence or absence of positive
symptoms, negative symptoms or disorganisation symptoms derived from the
Manchester Scale, for either gender. However, among men (but not women) under
the age of 36 years there was a positive association between giving a lifetime
history of non-alcohol substance misuse and having definite parkinsonism
(defined as a score of 2 or more on one item of the EPSE, P=0.001;
Pearson's 2=10.499, 1 d.f.). In this subgroup, there was no
significant association between a lifetime history of non-alcohol substance
misuse and the presence of akathisia (a score of two or more on the global
item of the BARS, P=0.072; Pearson's
2=3.246, 1 d.f.)
or anxiety (a score of two or more on the Manchester Scale item for anxiety,
P=0.053; Fisher's exact test). Furthermore, no relationship was found
between lifetime non-alcohol substance misuse and the presence or absence of
tardive dyskinesia (as rated either on the AIMS or TDS) or depression
(Manchester Scale).
Concurrent alcohol and non-alcohol substance misuse
The results of the alcohol questionnaire have been presented in detail
elsewhere (Duke et al,
1994). Reporting alcohol misuse was associated with giving a
positive non-alcohol substance misuse history (Pearson's
2=18.847, 1 d.f., P=0.0001). Only five subjects (four
White males and one White female) gave a history of alcohol misuse without
additional lifetime drug use. However, 20 of the non-alcohol
substance-misusing group reported no alcohol problems. Adding the five
individuals who admitted misusing alcohol but not drugs to the lifetime
substance misuse positive category made no significant difference to
the majority of the findings listed above. In men, the addition of such cases
reduced the statistical significance of the association between self-reported
lifetime substance misuse and akathisia and anxiety. Inclusion of those
misusing alcohol increased the association of lifetime substance misuse with
depression (as defined by a Manchester Scale item score of 2 or more) but the
finding was not statistically significant (
2 test;
P=0.095). No new findings resulted among women.
Anticholinergic drug misuse
Anticholinergic drug misuse (defined as deliberately taking more of an
anticholinergic drug than was prescribed in order to experience psychotropic
effects) was spread more evenly across the age groups than the misuse of
illegal drugs. It was associated with lifetime history of non-alcohol
substance misuse in those aged 36 years or older, but not in those
younger.
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DISCUSSION |
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Self-reported non-alcohol substance misuse in young males was significantly associated with the presence of parkinsonian symptoms. One possible explanation is that the dysphoric experience of parkinsonism may have prompted patients to misuse substances to gain some relief, in line with the self-medication hypothesis of substance misuse (Schneier & Siris, 1987; Krystal et al, 1999). However, our findings provide, at best, only weak support for a self-medication hypothesis, and more recent studies have failed to provide supportive evidence for such a notion (Salyer & Mueser, 2001). Given that the non-alcohol substance misuse reported by those with schizophrenia may simply reflect usage in the general population, the reasons for taking drugs also may be similar (Condren et al, 2001).
General limitations of the questionnaire method
Studies of populations without mental illness, comparing questionnaire
findings with the results of biological tests such as urine and hair analysis,
indicate that questionnaires substantially underestimate rates of recent use
of certain illicit drugs, notably amphetamines, cocaine and opioids
(Mieczkowski, 1991; Condren et al,
2001). This may be because the interviewees see these drugs as
being highly illegal or socially stigmatising, or because they fear the
possible consequences of disclosure. We therefore believe that our results
represent an underestimate, particularly of rates of recent stimulant and
opiate misuse. In particular, the finding that only 13 people admitted to
recent non-alcohol substance misuse is unconvincing, given the frequency of
self-reports of lifetime use and the results of other studies using biological
methods of assessment to support questionnaires (see
Table 3). As in the general
population (Cook et al,
1995), those with mental illness may selectively underreport
recent misuse of some illegal drugs to their families, to health professionals
and to researchers.
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Limitations of the SURSp
The information gathered on non-alcohol substance misuse using the SURSp
was limited to the maximum lifetime use of each substance and the amount of
each drug used in the preceding month, and omitted any assessment of drug
dependency. The underlying assumption was that, in the presence of a severe
mental illness, the use of comparatively small amounts of an illegal drug may
have serious consequences for the mental state of the user
(Drake et al, 1989). In this study, the numbers of people admitting to recent misuse of any
particular substance were too small to allow separate analysis. This was
unfortunate, because consequences of misuse of these various substances, with
their distinct pharmacological effects, would be expected to differ
considerably.
Comparison of findings with those of other studies
Previous studies of stimulant misuse among people with schizophrenia are
summarised in Table 3. Only
one, the ECA, is an epidemiological study. The remainder are studies of
selected groups such as clinic attenders and in-patients. Our study shows
findings broadly comparable with those of the only other UK study, that of
Menezes et al (1996),
which used the same screening questionnaire but studied people with a broader
range of diagnoses. The overall rate of substance misuse was higher in that
study, although the sample was an average of 8 years younger (mean age=42.3
years) than our own sample, and our findings suggest a marked propensity for
misuse of substances other than alcohol in younger patients. Further, their
study was of patients known to services, who may have been more symptomatic as
a consequence of their substance misuse.
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Clinical Implications and Limitations |
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LIMITATIONS
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Received for publication February 22, 2001. Revision received July 5, 2001. Accepted for publication July 6, 2001.
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