University Department of Psychological Medicine, Gartnavel Royal Hospital, 1055 Great Western Road, Glasgow G12 0XH, UK.
Correspondence: Tel: 0141 211 3927; fax: 0141 357 4899; e-mail r.cantwell{at}clinmed.gla.ac.uk
Declaration of interest None. This study was supported by the Chief Scientist Office for Scotland.
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ABSTRACT |
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Aims To examine the effects of comorbid substance use on symptoms, social functioning and service use in patients with schizophrenia.
Method Patients (n=316) with and without substance use problems from three centres participating in the Scottish Comorbidity Study were compared, using research interviews and case note review, on measures of symptoms, social functioning and service use.
Results Patients with substance use problems were younger, more likely to be male and had shorter duration of illness. They had more police contact and increased self-reported needs, but otherwise showed few differences when compared with those without such problems.
Conclusions The presence of problem substance use had only modest impact on service use, symptoms or social functioning for this group of patients with schizophrenia. This has important implications for service development to meet the perceived needs of this group.
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INTRODUCTION |
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METHOD |
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This study formed part of a wider investigation into the prevalence of substance misuse among patients with schizophrenia in three areas of Scotland when compared with locally recruited controls. Details of prevalence rates in comparison with controls may be found in the paper by McCreadie et al (2002). Ethical approval was obtained from the relevant local ethics committees and all participants gave informed, written consent before inclusion.
Assessment
All participants were interviewed by research nurses, who used sections 11
and 12 of the Schedules for Clinical Assessment in Neuropsychiatry (SCAN)
(World Health Organization,
1994) to identify lifetime (i.e. any time preceding
the year up to interview) and past year drug and alcohol use.
The three research nurses were trained in the use of this instrument and
reliability was checked by reviewing recorded interviews at several points
throughout the study. Basic demographic details, including age, gender,
ethnicity and social deprivation, were obtained. Social deprivation was
determined from the participants' post-codes, using the Carstairs Deprivation
Index (Carstairs & Morris,
1990). Service use was estimated by recording contacts with
primary care staff, community mental health team members, out-patient
services, depot clinics, general hospitals, accident and emergency
departments, police and other (e.g. voluntary) services within the past year.
Number of psychiatric admissions, days spent in hospital and use of the Mental
Health Act over the preceding 2 years were also recorded. Social functioning
was assessed using the Global Assessment Scale (GAS;
Endicott et al, 1976),
in addition to information on marital status, living arrangements and
employment. The Camberwell Assessment of Need (CAN;
Slade et al, 1999) was used to gauge subjective and keyworker-reported needs (both met and
unmet). In addition, all participants were interviewed by research
psychiatrists, who administered the Positive and Negative Symptom Scale
(PANSS; Kay et al,
1987) to assess current symptom severity. Regular reliability
checks, by reviewing recorded assessments, were also carried out for this
instrument throughout the study period.
For the purposes of this study, participants were identified as having problem use if they met ICD-10 research criteria for harmful use or dependence. Based on the SCAN interview, participants were further divided into those with problem use in the past year and those with lifetime use. Although it might be hypothesised that recent use is more likely to influence symptoms, social functioning and service use, lifetime use might also affect the course of illness and so is reported here as well.
To help corroborate the participants' reports of current use, every 20th patient was asked to give a urine sample (for cannabis measurement) and a hair sample (for measurement of opioids, sedatives, cocaine, stimulants, hallucinogens and volatile substances) to assess drug use in the previous 3 months (up to 30 days for cannabis). Substance use was also assessed by interview with keyworkers using a five-point rating scale (Drake et al, 1989). Laboratory analysis revealed no significant discrepancy with participants' own accounts of their drug-taking, but the accounts agreed relatively poorly with keyworker ratings (although in no consistent fashion). We thus relied on the extended research nurse interview (i.e. participant report) as providing the most reliable information on substance use.
Analysis
Chi-squared tests for categorical data and t-tests for continuous
variables were used for univariate analyses. As there were multiple
comparisons, only differences at the 1% level were regarded as
significant.
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RESULTS |
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Cannabis was the most commonly used drug, followed by opioids for current users and stimulants for lifetime users. Regarding alcohol, 49 (16%) reported problem use in the past year and 122 (39%) in the time before that. When combined, 64 (20%) had problem drug and/or alcohol use (hereafter referred to as problem substance use) in the past year and 141 (45%) at some time before that. Further details of substance use in this sample (including exact numbers with harmful use and with dependence) have been published separately (McCreadie et al, 2002).
Demographic findings
Comparisons of participants who were problem users and those who were not,
in terms of gender, age, ethnicity, social deprivation and illness duration,
are given in Tables 1 and
2. Younger age and male gender
were associated with problem use (either current or past), as was shorter
duration of illness. There was no difference in the age at onset between the
two groups, but those who were problem drug users in the past year had an
earlier age of onset of illness when examined separately (23.9 years
v. 27.9 years, P=0.002). Those with problem alcohol use in
the past year were also more likely to be in employment than their
non-problem-using counterparts. Numbers were too small to detect any
differences in ethnicity.
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Symptoms and social functioning
Symptoms were measured using sub-scale (positive, negative and general) and
total scores from the PANSS. Higher scores on the general sub-scale (which
includes anxiety and depression ratings) reached significance for the group
with problem substance use (past year) but this difference disappeared in the
total scores (Tables 3 and
4). On measures of social
functioning, GAS scores were not significantly different, nor was there any
difference in living arrangements or marital status. Those reporting problem
use (both past year and lifetime) did, however, have a greater self-reported
number of needs and higher mean needs rating (combined scores for partially
met or unmet need) (Tables 5
and 6).
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Service use
With the exception of increased attendance at depot clinics (22.5%
v. 11.2%, P=0.008; OR=2.3, 95% CI 1.0-5.2) for lifetime
problem substance users, and increased contact with psychiatrists (95.3%
v. 82.3%, P=0.01, OR=0.2, 95% CI 0.05-1.1) for past-year
substance users, participants with problem drug or alcohol use were no more
likely than those without substance use problems to have accessed primary care
or to have had contact with other specific individuals in secondary care
services (community psychiatric nursing, occupational therapy, psychology or
social work) within the preceding year. Neither were they more likely to have
attended general hospitals or accident and emergency departments. They did,
however, have more police contact (past-year users 34.9% v. 14.9%,
P<0.001, OR=3.1, 95% CI 1.3 to 7.0; lifetime users 29% v.
10.8%, P<0.001, OR=3.4, 95% CI 1.5 to 7.5). This reflected both
greater reporting of crimes committed against the participants, and police
contact for other reasons. Our method did not allow a further breakdown of
these data. Numbers of admissions (past-year users 0.67 v. 0.89,
P=0.259, 99% CI -0.6 to 0.16; lifetime users 0.85 v. 0.6,
P=0.113, 99% CI -0.59 to 0.55), days admitted (past-year users 96.7
v. 61.8, P=0.211, 99% CI -19.9 to 89.8; lifetime users 78.3
v. 98.5, P=0.371, 99% CI -64.7 to 24.2) and detentions under
the Mental Health Act (past-year users 0.2 v. 0.32, P=0.225,
99% CI -0.37 to 0.13; lifetime users 0.31 v. 0.16, P=0.066,
99% CI -0.58 to 0.34), all within the previous 2 years, also showed no
significant difference.
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DISCUSSION |
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Methodological issues
One possible explanation for our finding is that those identified but not
interviewed were more likely to be substance users. Although we cannot
entirely rule this out, no difference emerged on any of the demographic and
clinical factors that we were able to ascertain. Although the rates for
problem drug use in the past year in our sample are a little lower than those
reported in other UK studies (e.g. Menezes
et al, 1996), the participants in the latter tended to be
urban-based and younger. Underreporting could also have led to our finding of
lack of difference. Our method of case finding was detailed and comprehensive,
and corroborative hair and urine analyses in a subsample did not reveal recent
use in those who denied it. When all other factors (such as age, geographical
setting and diagnosis) are taken into account, the proportion of patients who
were problem substance users is unlikely to differ greatly in our sample from
those in other recent UK studies (Menezes
et al, 1996; Brown,
1998).
Reasons for the lack of difference
Are there other possible explanations for the lack of difference in this
sample? Although most studies of chronically ill populations have found a
detrimental effect of substance use, in many the participants were drawn from
hospitalised, urban samples. Our patients were predominantly community-based,
and came from a mix of urban and rural settings. Their level of problem
substance use and any associated consequences may therefore more accurately
reflect patterns throughout the UK. Similar lack of effect in a community
sample was reported by Zisook et al
(1992). Warner et al
(1994), who also found little
adverse consequences of substance use, suggest another explanation
that the finding of poorer outcome for patients with comorbid substance misuse
might be mediated through non-compliance with treatment. They suggest that
assertive community support might minimise this effect and thus any adverse
consequences. We could not assess compliance, but all three areas in this
study have well-developed community mental health teams and easy access to
support for patients. Last, it has been suggested that patients with
schizophrenia who are substance misusers might be a more able group at onset
(Arndt et al, 1992)
and that those with the most severe forms of illness are too disabled to
engage in drug-seeking activity. Our study design could not test this
hypothesis.
Relevance of our findings
These results should be interpreted with caution. They do not suggest that
problem substance use in itself is of no consequence to this group. By
definition, these people have suffered through this misuse. As has been
previously noted, we cannot predict what level of functioning such patients
might have had if they were not substance users
(Zisook et al, 1992),
and there remains an onus on general psychiatry and specialist addiction
services to address their needs. What this paper does add is the
interpretation that, in a sample that is older and more representative of
urban and rural populations than samples in other UK studies, problem
substance use may inflict less-severe damage than previously suspected.
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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 May 7, 2002. Revision received October 30, 2002. Accepted for publication November 12, 2002.