Demographics of Substance Use in Patients With Schizophrenia

The proportion of schizophrenia patients suffering from a comorbid drug or alcohol use disorder varies tremendously in published studies, from as low as 10% to as high as 70% (Mueser et al. 1990). The observed range is partially due to variability in the diagnostic criteria employed for schizophrenia, sample demographic characteristics (e.g., male vs. female, urban vs. rural), the types of patient populations studied (e.g., inpatient vs. outpatient), and different criteria for defining drug and alcohol disorders (e.g., DSM-III-R diagnosis, positive urine toxicology screens, rating scales) (Mueser et al. 1990). Although structured clinical interviews have been found to produce the most reliable diagnoses, these are time consuming and expensive due to the need for trained personnel, and therefore are not often used in clinical studies (Mueser et al. 1995). Surveys conducted exclusively in inpatient settings tend to produce higher rates of substance use disorders, in part because persons with dual disorders (i.e., substance use and another major Axis I disorder) are more likely to enter into treatment because exacerbation of either problem may become a focus of clinical attention (Mueser et al. 1995).

The Epidemiologic Catchment Area (ECA) study revealed that 47% of all individuals in the United States with a lifetime diagnosis of schizophrenia or schizophreniform disorder met criteria for some form of substance abuse or dependence (33.7% for alcohol disorder and 27.5% for another drug abuse disorder) (Regier et al. 1990). This figure is comparable with the range of 40%-60% lifetime prevalence gleaned from an analysis of 47 published studies of schizophrenia patients with sample sizes of at least 30 in which the criteria for abuse or dependence were clearly delineated (Cantor-Graae et al. 2001). The authors of this review also found that studies in which more than one method of diagnosis was employed (e.g., chart review plus interview) yielded higher prevalence rates compared with studies that relied on a single method. Regardless of method, in community samples of patients with schizophrenia that are not composed solely of inpatient groups, a figure of approximately 50% lifetime prevalence is found repeatedly. This finding is replicated even from sources outside the United States, such as the recent study combining both structured interview and chart review of 87 patients with schizophrenia in Malmo, Swe den, which noted a lifetime prevalence of any substance use disorder of 48.3% (47.1% for alcohol alone or in combination with other drugs, 26.4% for alcohol only) (Cantor-Graae et al. 2001).

In addition to the lifetime prevalence data, the ECA study found that the odds of having a substance abuse diagnosis were 4.6 times greater for persons with schizophrenia compared with the rest of the population, with the odds of alcohol disorders more than 3 times greater and those of other drug disorders 6 times greater (Regier et al. 1990). Among all substances, nicotine is clearly the most frequently abused agent, with prevalence estimates ranging from 70% to 90%, over 3 times greater than the general population estimate of approximately 25% (Davidson et al. 2001). (See more extensive discussion in Chapter 5, "Nicotine and Tobacco Use in Schizophrenia.") Excluding nicotine use, the ECA study results are consistent with other prevalence studies of schizophrenia demonstrating that alcohol tends to be the most frequently abused agent (20%-60%), followed by cannabis (12%-42%) and cocaine (15%-50%) (Chambers et al. 2001). Use of amphetamines (2%-25%), hallucinogens, opiates, and sedative/hypnotics is less common.

The most consistent findings with regard to demographic characteristics are that those who are younger, were younger at age of schizophrenia onset, or are male are more likely than those who are older and female to abuse drugs or alcohol (Hambrecht and Hafner 2000). It is important to note, however, that evidence is accumulating to document that substance use difficulties among women are not sufficiently recognized, and that women with schizophrenia and comorbid substance disorders are less likely to receive substance abuse treatment (Alexander 1996; Comtois and Ries 1995). The undertreatment of women may lead to unrealistically low prevalence estimates in retrospective chart review studies, yet even in interview studies male gender appears as an independent risk factor after the disparities in gender frequency are controlled for among study participants (Cantor-Graae et al. 2001). There is also evidence from the Malmo, Sweden, cohort and other studies indicating that the onset of substance use in schizophrenia occurs at a younger age in males than in females (Salyers and Mueser 2001).

There are conflicting data regarding the functional capabilities of substance-using patients with schizophrenia compared with non-substance users with severe mental illness. In one of the first studies to examine this issue, Mueser et al. (1990) reported findings on 149 recently hospitalized patients who met DSM-III-R criteria for schizophrenia, schizoaffective disorder, or schizophreniform disorder, and found lower educational levels among the substance-abusing severely mentally ill compared with severely mentally ill patients without substance use disorders. Yet later studies have indicated that substance-using patients with schizophrenia might be more functional than non-substance users. Arndt and colleagues' study of 131 schizophrenia patients with and without comorbid substance use (n =64 and 67, respectively) matched for symptomatology and clinical history noted better premorbid adjustment among the so-called pathological substance users (Arndt et al. 1992). In another study, comparing 34 patients with schizophrenia who had histories of substance abuse with 17 patients with schizophrenia who were abstinent (Zisook et al. 1992), the substance abusers were more likely to have been married or gainfully employed.

The most comprehensive attempt to correlate symptomatology and social function with substance use among patients with schizophrenia was performed by Salyers and Mueser (2001), employing 404 patients with a history of recent hospitalization (i.e., prior 3 months) recruited from within a large multicenter psychosocial treatment strategies study. Individuals were ages 18-55, agreed to receive fluphenazine decanoate but not other major psychotropic agents, and received at least three of the monthly assessments of psychiatric symptoms, social functioning, side effects, and substance use over the 3- to 6-month follow-up period. It should be noted that those who were homeless or transient and patients with active ongoing physical dependence (or with suspected drug-induced psychosis but not schizophrenia) were excluded.

In this study, those who consistently reported low or no use of substances scored significantly higher than regular drug or alcohol users on assessments of negative symptoms, particularly the social amotivation and diminished expression scores, although the groups were comparable on ratings of psychotic symptoms (Brief Psychiatric Rating Scale [BPRS]) and distress (Symptom Checklist-90). There were also no significant differences in ratings of tardive dyskinesia, parkinsonism, or akathisia between users and nonusers, although those who reported the greatest frequency of social problems had higher akathisia ratings irrespective of degree of substance use. As one might expect from those who manifest greater negative symptomatology, the low- or no-use group also demonstrated more severe impairment in leisure activities and less frequent social contacts. Although the substance users enjoyed a higher level of social functioning, the drug users in particular reported significantly greater interpersonal problems compared with the low-/no-use group. Interestingly, despite the greater social functional status of substance users, this group had an earlier age of onset for their mental illness and more hospitalizations than the low-/no-use group.

The biological correlate of higher functional status can be seen in work by Scheller-Gilkey and colleagues, who examined differences in magnetic resonance imaging scans for a large sample (n = 176) of schizophrenia pa tients. The investigators noted the rate of gross brain abnormalities among both alcohol and drug abusers to be less than half the rate found among patients with no history of alcohol or substance abuse, although this finding did not reach the 0.05 level of statistical significance (Scheller-Gilkey et al. 1999).

Demographic differences exist between urban and rural groups with schizophrenia, especially with regard to housing, and there are also data to suggest that patterns of substance use differ between the two settings. Alcohol use alone or in combination with cannabis is likely to be present in schizophrenia patients living in a rural setting, whereas the use of multiple substances, particularly cocaine, is common in urban settings (Mueser et al. 2001).

Perhaps one of the most important demographic trends recently recognized among the severely mentally ill is the high prevalence of human immunodeficiency virus [HIV], hepatitis B, and hepatitis C (Meyer in press). Whereas the former may be transmitted sexually, hepatitis C in the United States is transmitted primarily by use of shared needles among intravenous drug users. (This topic is covered in detail in Chapter 7, "HIV and Hepatitis C in Patients With Schizophrenia.") Patients with schizophrenia are more likely to engage in high-risk behavior resulting in HIV or hepatitis C infection, yet there is remarkably little in the way of data about the extent of intravenous drug abuse in this disorder. In one large study of mentally ill persons (65% of whom had schizophrenia or schizoaffective disorder), 62.1% of those infected with hepatitis C (n = 145) reported a lifetime history of intravenous drug abuse (IVDA), whereas only 5.1% of the hepatitis C-negative group (n=604) reported a history of IVDA (Rosenberg et al. 2001). Among the HIV-positive persons with severe mental illness, the lifetime prevalence of IVDA was 8.6% compared with 1.4% for the HIV-negative group (Rosenberg et al. 2001). Another, smaller study of 91 schizophrenic patients employing two self-reporting measures found a 22.4% lifetime prevalence of injected drug use; moreover, despite IVDA and high-risk sexual behaviors, 65% reported no concern with HIV infection, and AIDS knowledge was significantly lower among the schizophrenic patients than the control group, particularly among those with long-standing illness and multiple psychiatric admissions (Grassi et al. 1999).

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