Schizophrenia and Substance Abuse: Prevalence Issues* NADY EL-GUEBALY, M.D.' AND DAVID

C. HODGINS, Ph.D. 2

A review of studies of the prevalence of substance abuse among schizophrenics suggest that both demographic and environmental factors are strong determinants of the extent of substance abuse in this population as well as the type of substances used. In a mid-sized Canadian city, a sample of schizophrenic patients referred to a dual diagnoses clinic were administered the Addiction Severity Index. With age and gender included as a factor, no significant differences were found in the choice or length of use of most drugs between diagnostic groups, contrary to some other reports from large urban centres. Compared with a population ofa similar age, there were fewer regular and more former drinkers among the schizophrenic patients. The choice ofother substances by the sample reflected the pattern of use in the population at large. This approach to prevalence provides a more balanced perspective of the substance abuse by schizophrenics. The major targets for prevention remain the alcohol, caffeine and tobacco consumption.

A

ccording to epidemiological surveys, the prevalence of substance abuse ranges widely among psychiatric samples, depending on the definition, treatment setting, demography and diagnosis (l). According to the NIMH Epidemiological Catchment Area Survey (2), 1.5% of the population has a lifetime diagnosis of schizophrenia or schizophreniform disorder and, of these individuals, 47% have met the criteria for some form of substance abuse dependence (33.7% met the criteria for an alcohol disorder and 27.5% for another drug disorder). The odds of suffering from any substance abuse disorder are 4.6 times higher among schizophrenics than the rest of the population; the odds of having an alcohol disorder are more than three times higher, and six times higher for other drug disorders (3). A review of 18 studies comparing schizophrenics' use of substances with control populations of other psychiatric patients or non patients suggested a non random distribution. Depend-

*Manuscript received July 1991, revised December 1991. 'Director, Department of Psychiatry, Foothills General Hospital; Professor and Head, Department of Psychiatry, University of Calgary, Calgary, Alberta. 2Division of Psychology, Foothills General Hospital; Adjunct Assistant Professor, Department of Psychiatry, University of Calgary, Calgary, Alberta. Address reprint requests to: Dr. N. el-Guebaly, Department of Psychiatry, Footjills Hospital, 1403 - 29 Street NW, Calgary, Alberta T2N 2T9

Can. J. Psychiatry Vol. 37, December 1992

ing on the study, schizophrenic patients' use of amphetamines, cocaine, cannabis, hallucinogens, inhalants, caffeine and tobacco was reportedly greater than or equal to that of the control groups. The use of alcohol, opiates and sedative hypnotics was significantly less than or equal to that of the control groups. The extent to which the findings can be generalized is limited by the sampling heterogeneity of the 18 studies along with the lack of standardization of the diagnoses of schizophrenia and substance abuse (4). Another potential complicating factor is the difference between substances as risk factors for psychotic experiences. In the NIMH catchment area survey, males with alcohol disorders were eight times more likely to develop delusions or hallucinations than the males in the general population and women with alcohol disorders were three times as likely. Daily users of marijuana, on the other hand, were only twice as likely to develop psychoses (5). A recent, thorough methodological review of studies (6) examining alcohol or illicit drug abuse among schizophrenics (excluding samples selected on the basis of a history of abuse) suggested that the prevalence of substance abuse in patients with schizophrenia was comparable to that of the general population except that schizophrenic patients were more likely to use stimulants and hallucinogens. Both demographic and environmental factors were strong determinants of substance abuse among the samples of schizophrenic patients. The need to assess substance abuse in more than one diagnostic group and in non patient controls was'emphasized. This paper describes our experience in a mid-sized Canadian city with a sample of schizophrenic patients referred to a dual diagnoses clinic for substance abuse. The substance abuse profile of these patients is compared with the profile of patients referred to the clinic with other diagnoses (affective disorders, anxiety disorders, and other Axis I disorders) and with the profile of individuals in the general population. Method

To respond to the needs of patients with both substance abuse and another psychiatric disorder, a dual diagnoses clinic was established in 1988 in the ambulatory care component of the department of psychiatry of an acute care teaching hospital. Over two years, the clinic, which is the only one of its kind in the province of Alberta, received 250 referrals. Each patient's substance use was assessed using the Addiction Severity Index (ASI), a structured interview which takes approximately one hour to administer. The instrument 704

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accounts for all aspects of addiction - it assesses the need to treat the substance use, and medical, legal, family/social, employment/support and psychiatric problems (7). The instrument has been validated with populations of addicted patients (8) as well as a psychiatric population (9). In addition to the ASI, each patient's diagnosis was established according to DSM-III-R criteria, and the use of substances in alI groups was compared. The time involved in administering the ASI made it unsuitable as a substance abuse screening device for those at the schizophrenia outpatient clinic. We therefore included two established self-report screening instruments as part of a health habit survey; the survey was administered to every second patient at the clinic over a period of ten weeks. The Michigan Alcoholism Screening Test (MAST) is a 24 item self-report instrument that measures the severity of general alcohol-related deterioration or involvement (10). A cut-off score of 5 is used to screen for alcoholism. Psychometric studies indicate that this instrument has adequate reliability and validity (11,12). The Drug Abuse Screening Test (20 item DAST) yields a self-report quantitative index of problems related to both prescription and non prescription drug abuse (13). A cut-off score of 6 or more indicates clinicalIy significant drug abuse. The results of item and factor analyses suggest that the instrument is reliable and valid in psychiatric populations (14).

subsample of Albertans, ages 20 to 69 (n = 919), in order to make the most appropriate comparisons. Statistical analyses were carried out using chi-squares for categorical variables, and t-tests and analyses of variance for continuous variables.

Results Substance Use Among the Specialty Clinic Referrals

Of the 250 patients referred to the clinic, 29 had a primary diagnosis of schizophrenia (see Table I). There was a statistical difference in age (F(4,249) = 3.4, P < 0.001) and gender (chi-square = 14.6, df = 4, P < 0.006) between diagnostic groups; the schizophrenia group was younger on average and had the highest proportion of males. Because of these demographic differences, age was covaried and gender was included as a factor in subsequent statistical analyses. The age range of the sample was 18 to 69 years and subjects were predominantly Caucasian (96% Caucasian, two percent Native, two percent other). The average education was 11.5 years (SD = 2.7) and did not differ among diagnostic groups. Compared with the other groups, the schizophrenics were more likely to be unmarried (chi-square = 17.5, df = 8, P < 0.05), less likely to be employed (chi-square = 20.1, df = 8, P < 0.01) and reported more psychiatric inpatient admissions (5.4 versus 2.7 overall; F(4,242) = 3.6, P < 0.01). When age was covaried, no statistical differences were found among the referred groups on most of the addiction severity indices. There was no difference in either the lifetime use of alcohol (number of months of regular use) (see Table II) or in the number of days the subject used alcohol in the

Finally, that same year we conducted preliminary comparisons between these figures and the results of the National Alcohol and Other Drug Survey for the Province of Alberta (15). The data presented in this report are from the Table I

Demographic Characteristics of Groups Patients Referred to the Dual Diagnoses Clinic

Total subjects Males (n) Females (n) Age mean (years) AgeSD Education mean (years) SD Education SD

Schizophrenia

Affective Disorders

Anxiety Disorders

Other Axis I Disorders

Substance Abuse Only

Overall

29 25 4 32.1 8.7 10,7 2.0

64

33 31 37.0 9,8 12.0 3.3

29 15 14 39.7 9,1 11.3 2.9

30 23 7 32.7 7.7 11.6 2.4

98 57 41 35.5 10.1 11.4 2.5

250 153 97 36.7 9,7 11.5 2.7

41 31 28

27 30 43

34 25 41

29 28

48 3 48

40 23 37

50 21 29

40

Marital Status • Divorced or separated

3 24

• Never married

72

27 31 42

14 28 59

34 25 41

• Married (%)

44

Employment status • Employed • Unemployed • Not in work force

21 38

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CANADIAN JOURNAL OFPSYCHIATRY Table II Substance Use by Diagnosis t Other Axis I Disorders (n = 30)

Substance Abuse Only (n = 98)

Affective Disorders (n =64)

Anxiety Disorders (n =29)

168.7 98.7 29.0

196.4 102.8 60.0

220.7 109.3 23.0

151.1 95.9 24.0

173.9 103.4 86.0

25.6 42.3 7.0

64.2 103.8 15.0

57.3 64.7 10.0

54.5 60.1 4.0

116.7 101.1 23.0

11.1 8.7 8.0

70.3 92.7 21.0

116.1 118.9 14.0

77.3 127.4 7.0

74.5 101.2 35.0

4.2 5.2 4.0

20.8

53.0

15.2

46.0

32.7 13.0

69.2 3.0

12.1 4.0

49.9 21.0

40.2 34.9

48.7

• SD

14.1 14.7

36.0 48.6

• n*

8.0

17.0

72.3 3.0

4.0

44.6 74.8 16.0

111.1 65.7 15.0

128.4 82.7 30.0

60.0 70.2 7.0

101.2 59.1 13.0

110.5 71.5 41.0

58.6 73.0 11.0

60.0 52.6

126.0 76.4

52.8 46.6

12.0

2.0

34.7 23.4 6.0

44.0 30.2

0.0 0.0

60.0

• SO

68.8 102.8

• n*

5.0

3.0

0.0

67.9 2.0

4.7 6.4

91.3 62.3 15.0

116.7 168.9 36.0

125.2 108.9 13.0

119.0 86.0 15.0

Months of Use/Lifetime

Schizophrenia (n =29)

Alcohol • Mean • SD

• n*

Opiates • Mean • SO

• n* Sedatives • Mean • SO

• n* Cocaine • Mean • SO

• n*

Amphetamines • Mean

Cannabis • Mean • SD

• n*

Hallucinogens • Mean • SO

• n*

17.0

Inhalants • Mean

3.0

Months of use> one substance/day • Mean • SD

• n*

79.0 69.8 55.0

'the number of subjects reporting regular use of the substance for one month or more. Chi-square analyses were used to examine between-diagnostic differences in the number of users where sample size allowed; tN = 250

previous month. In all groups, alcohol was consumed for the longest time and by the greatest number of people. Males in all referred groups reported drinking to intoxication significantly more than females (F(4.244) = 13.9, P < 0.(001). No significant differences were found in the choice or length of use of most drugs among diagnostic groups either

during the subject's lifetime or during the previous 30 days. Table II lists the number of users and the number of months they had been using the substance during their lifetime (only for the sake of clarity). However, during the previous 30 days, more people with anxiety disorders reported using sedative hypnotics and minor tranquilizers (chi-square = 9.34, P

Schizophrenia and substance abuse: prevalence issues.

A review of studies of the prevalence of substance abuse among schizophrenics suggest that both demographic and environmental factors are strong deter...
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