Epidemiology
Estimates of the prevalence of substance use disorders among psychiatric patient populations vary widely, reflecting factors such as the use of samples with acute versus nonacute illnesses, the geographic site of studies (for example, urban versus rural or West versus East), and the availability of illicit drugs in the study location. Studies in the United States confirm that the prevalence of substance use disorders among patients with severe mental illness is higher than in the general population (
2). This finding has been corroborated by the National Comorbidity Survey (
4).
A second finding with major clinical implications is that the co-occurrence of severe mental illness and substance use disorders is associated with an increased probability of receiving some kind of treatment. The 1992 National Longitudinal Alcohol Epidemiologic Survey (
5) showed that respondents with past-year alcohol use disorders were twice as likely to seek help for their alcohol problems if they also had either a comorbid drug use disorder or major depression, and they were five times more likely to seek help when both comorbid conditions were present (
5).
International prevalence studies have revealed that persons with severe mental illness have significantly higher rates of substance use—particularly of alcohol, cannabis, and amphetamines—than the general population (
6,
7). Such studies suggest that the consequences of substance abuse among patients with severe mental illness may be mediated by differences in the types of mental health services available in these countries.
For example, Fowler and associates (
8) found higher rates of alcohol, cannabis, and amphetamine use among patients with schizophrenia relative to the general population in Australia. The researchers also found that although younger males with more involvement with the criminal justice system used substances, they did not report increased risk for suicide or hospitalization, in contrast to findings in many U.S. studies. Such differences in consequences could be attributable to the treatment strategies of the Australian mental health system, which places greater reliance on the use of mobile crisis treatment units for in-home management of acute psychotic episodes.
Screening and assessment
Screening. Patients with severe mental illnesses should receive routine screening for any regular use of nonprescribed psychoactive drugs for three reasons (
9). First, attempts at controlled use of psychoactive substances by individuals with severe mental illness are likely to lead to a substance use disorder over time (
10). Second, use of even small amounts of alcohol or other drugs is likely to be associated with negative outcomes among these individuals. Finally, persons with severe mental illness are likely to be unaware of or confused about the consequences of their substance use, and any report of regular use is likely to be associated with substance use disorder (
11).
A variety of self-report screens for substance use disorders can be completed as part of an initial intake interview for a patient with a severe mental illness. Among them are brief instruments such as the Drug Abuse Screening Test (
12), the Michigan Alcoholism Screening Test (MAST) (
13), the CAGE questionnaire (
14), and the Dartmouth Assessment of Life Style Instrument (
15). However, a clear consensus supports combining the use of self-reports with collateral reports and laboratory tests (
9).
Assessment. One of the more commonly used standardized assessment instruments in the substance use disorder field is the Addiction Severity Index (ASI) (
16). Appleby and colleagues (
17) examined the validity of the ASI in a sample of 100 patients consecutively admitted to a public mental hospital, two-thirds of whom had a diagnosis of a psychotic disorder. In that study, the ASI was compared with the CAGE questionnaire, a drug abuse version of the CAGE, the Chemical Abuse and Dependence Scale, the short form of the MAST, and the Drug Abuse Screening Test. The researchers found strong correlations between the ASI and the other scales and concluded that even with a minimum cut-off score, the ASI alcoholism scale is diagnostically as accurate as the CAGE or the short MAST for outpatients with psychiatric illnesses.
However, recent studies have raised questions about the performance of the ASI. Lehman and colleagues (
18) compared the performance of the ASI with that of the Structured Clinical Interview for DSM-III-R in a sample of 435 inpatients at two inner-city psychiatric hospitals. The researchers used receiver operating characteristic analysis, which permitted assessment of the optimal threshold of ASI alcohol and drug composite scores to detect
DSM-III-R substance use disorders. They found that the sensitivity values for the ASI alcohol and drug use composite scales at extremely low ASI scores (.01) are only .81 and .82, respectively. They concluded that the ASI should not be used by itself to detect substance use disorders among psychiatric inpatients. Zanis and associates (
19) made similar observations in an examination of the validity and the test-retest and interrater reliabilities of the ASI in a sample of 62 outpatients with severe mental illness.
Corse and colleagues (
20) described a qualitative study of subject and interviewer reactions to and perceptions about the ASI. They found that the ASI appears to underestimate subjects' substance abuse problems for three reasons. First, the definition of "regular use" used in assessing substance use imposes a cutoff of at least three times a week. Although this cutoff works well for the general population, patients with severe mental illness may exhibit patterns of less frequent weekly use that are associated with more serious consequences but that are not picked up.
Second, the ASI lacks questions that explore the interactive effects of severe mental illness and substance use. Finally, the drug and alcohol treatment history elicited by the instrument assumes that this treatment is delivered in the alcohol and drug specialty treatment sector, whereas most treatment for patients with severe mental illness occurs in medical or mental health settings.
The researchers offered specific suggestions for making the ASI more relevant for assessments of patients with severe mental illness. They include creating a psychiatric symptom checklist; adding questions about isolation, estrangement, and patients' relationships to the social and family problems sections; shortening the intervals over which respondents have to report their housing arrangements; and probing the extent to which patients rely on others.
Carey and associates (
21) reported preliminary data on the use of the Time Line Follow Back, which uses a calendar and various aids to memory to help patients recall their use of alcohol and other substances over time intervals of varying lengths (
22). Carey and associates compared results of the Time Line Follow Back over a 30-day interval with results of the ASI's 30-day assessment of alcohol use in a sample of 79 outpatients with severe mental illness. They found an excellent level of agreement between the two assessment instruments (kappa coefficient of .79), and a correlation of .75 between the two approaches on the number of days respondents reported that they had been drinking. The Time Line Follow Back procedure may actually yield higher estimates of drinking than the ASI for a 30-day interval (
23). Given that even moderate amounts of alcohol or other substance use may lead to adverse consequences for persons with severe mental illness, the Time Line Follow Back appears to offer a highly promising assessment approach that should be further examined in future research.
Self-reports. The screening and assessment instruments discussed above rely on the use of self-reports, a source of data that continues to be viewed with suspicion by many clinicians and researchers. However, an important shift in perspective on the use of self-reports is taking place. The old question of whether self-reports are valid is being replaced by questions about when and under what circumstances self-reports of substance use are likely to be valid and reliable.
Shaner and colleagues (
24) conducted an open trial with 108 subjects with schizophrenia using supplements to a routine clinical evaluation that included a semistructured interview for recent and lifetime use of alcohol and other drugs. Clinicians failed to recognize cocaine use among 30 percent of the patients who denied cocaine use but whose urine toxicology tests were positive for cocaine. The poor reliability of the self-reports highlights the need for collection of collateral information.
Specific recommendations for improving self-report data include ensuring the sobriety and mental stability of the respondent when the assessment is being conducted, using interview approaches rather than paper-and-pencil self-report instruments, using verification techniques and multiple sources of data, establishing adequate rapport between interviewer and respondent, and providing respondents with assurances of confidentiality.