Journal of Mental Health (2001) 10, 2, 175–188 The prevalence and characteristics of co-occurring serious mental illness (SMI) and substance abuse or dependence in the patients of Adult Mental Health and Addictions Services in eastern Dorset NICK VIRGO1, GERALD BENNETT1, DAVID HIGGINS1, LISA BENNETT1 & PETER THOMAS2 1Dorset HealthCare NHS Trust & 2Bournemouth University, Bournemouth, Dorset, UK Abstract Researchers interviewed key workers of all NHS inpatient, day-patient and outpatient Adult Mental Health (AMH, n=708) and Addictions (n=313) Services in eastern Dorset. ‘Dual diagnosis’ (co- occurring severe mental illness (SMI) and substance abuse or dependence) occurred in 12% of addictions, 12% of all AMH, and 20% of SMI, AMH patients (range 10% rehabilitation to 41% acute wards). Most ‘dual diagnoses’ in AMH were alcohol and/or cannabis abuse with psychoses, and in addictions heroin dependence and/or alcohol abuse or dependence with depression. Compared with other AMH, SMI patients, AMH ‘dual diagnosed’ patients were younger; were more often male, in less stable accommodation, unemployed, with more than one psychiatric diagnosis and personality disorder; and tended to have more crises and pose greater risk to themselves and others. Compared with ‘dual diagnosed’ addictions patients they were less involved with drugs, at less risk of abuse by others and less often acknowledged dual problems. Introduction over one third of people with alcohol disorders and over half of people with drug disor- Little is known about the UK prevalence of ders had experienced at least one mental substance use disorders in seriously mentally disorder in their life. Among a sub-sample ill (SMI) patients, or how SMI patients mis- drawn from mental health treatment settings, using substances differ from those who do Regier et al. (1990) found a 37% lifetime not. Far more research has been conducted in prevalence of alcohol abuse and a 20% 6- North America, including two large, multi- month prevalence of substance abuse (alco- centre community studies. Among all people hol 14%, drugs 8%). Reviewing other US with mental illness, Kessler et al. (1996) prevalence studies, Mueser et al. (1995) found found a 15% 12-month prevalence of sub- that most had shown that between 25% and stance abuse and Regier et al. (1990) an 11% 35% of people in treatment settings and with 6-month and 29% lifetime prevalence. Also, severe mental illness (SMI), had had a sub- Address for Correspondence: Nick Virgo, Department of Psychological Therapies, Herbert Hospital, Alumhurst Road, Bournemouth BH4 8EW, UK. Tel: 01202 765323; Fax: 01202 760036; nick.virgo@dorsethc- tr.swest.nhs.org.uk ISSN 0963-8237print/ISSN 1360-0567online/2001/0200175-14 © Shadowfax Publishing and Taylor & Francis Ltd DOI: 10.1080/09638230020023732 176 Nick Virgo et al. stance use disorder in the past 6 months. and substance use and dependence are pre- American mental health patients who misuse sented by Meltzer et al. (1996a,b) and by substances have worse functioning in mental Farrell et al. (1998). The results of a private health, social stability, treatment compliance, household survey and a survey of hospitals, legal problems, HIV infection and family hostels and residential homes illustrate quan- stress than others (Drake & Brunette, 1998; tities consumed rather than problems. They Osher & Drake, 1996). The generalisability found that 7% of people with schizophrenia, of these findings to the UK is undetermined, 18% with affective disorders and 22% with given important differences between the two neurotic disorders reported ever using drugs. nations including their patterns of substance Examining alcohol, they found that 16% of use and their mental health and addictions people with schizophrenia, 18% with affec- services. tive disorder and 21% with neurotic disorder British studies have been limited to inner had been drinking over the recommended city London or very select SMI populations limits for the normal population, 14 standard or have approached substance misuse from units a week for women and 21 for men. The examining consumption rather than conse- sample was of people in stable institutional quences. Duke et al. (1994) found a 22% care (not exclusively specialist treatment set- lifetime prevalence of alcohol abuse in peo- tings), which did not include acute care. It is ple with schizophrenia living in the South thus reasonable that the figures are lower Westminster area of London, including those than those from other studies of people in not in contact with mental health treatment treatment settings. services. In Camberwell London, in 171 This non-metropolitan UK study aimed to people with any psychotic illness who were establish the lifetime and point prevalence of younger and all drawn from mental health substance abuse and dependence among all treatment services, Menezes et al. (1996) current SMI patients of all services of an found a 42% lifetime prevalence of alcohol NHS Trust, not just those with psychosis and abuse, which is comparable to the 37% of including those of specialist addiction serv- Regier et al. (1990). Examining 12-month ices; to assess how far US-found differences prevalence, they found 36% for any sub- between substance misusing and other SMI stance abuse (alcohol 32%, drugs 16%) and patients occurred in this sample; and to detect draw comparison with the very close results differences between ‘dually diagnosed’ pa- of a study in New England (Drake & Wallach, tients of specialist addictions services and 1989), which used the same method of case those of other adult mental health services. identification. Cantwell et al. (1999) found a 37% 12- Method month prevalence of drug use or drug or alcohol misuse in first episode psychosis The study was carried out in an NHS Trust patients in Nottingham. This study did not serving a community on the south coast of use the DSM based definitions used in the England. The population of 450,000 in- two aforementioned studies but included any cludes a large conurbation (of Bournemouth, drug use of at least once per month in the Poole and Christchurch) surrounded by a preceding year. The National Psychiatric rural belt of small market towns (e.g. Morbidity Survey in England results as they Wimborne) and holiday resorts (e.g. relate to co-occurrence of mental disorder Swanage). The AMH Service for this com- Prevalence of substance misuse in SMI 177 munity consisted of seven multidisciplinary, were to be discussed. They were encouraged specialist Community Mental Health Teams to read the case notes beforehand and to bring (CMHTs) linked to primary health care teams, them to the interview. Interviews took about an acute hospital, residential and day treat- 60 minutes and covered an average of 12 ment and rehabilitation units, and a group patients. therapy treatment unit. The Addictions Serv- Statistical analysis ice provides community drug and alcohol teams, a detoxification ward and an absti- The principal aim was to compute the over- nence-oriented, day treatment unit for sub- all prevalence of co-occurring serious men- stance dependence. tal illness and substance abuse or dependence together with its 95% Confidence Interval Design (CI) and then to do the same for each compo- To establish (A) what proportion of the nent of the services. To compensate for the current patients of an NHS Trust’s (1) Adult fact that CMHTs were underrepresented, a Mental Health (AMH) and (2) specialist Ad- weighted analysis was carried out when data dictions Services were currently diagnosed from the different CMHTs were combined, with or met the criteria for a severe mental with or without data from the other services illness (SMI) and (B) what proportion of (Lee et al., 1989). Patients studied in each those SMI patients had current substance CMHT were weighted by the inverse of the abuse or dependence, thus calculating the probability with which they were sampled in point prevalence of ‘dual diagnosis’ in each order to ensure that the estimates of preva- arm of the service. To then compare charac- lence were not biased by the sampling strat- teristics of (C) AMH SMI patients with cur- egy. The analysis was carried out using SPSS rent substance abuse or dependence with for Windows Version 6.1 (Norusis, 1993). AMH SMI patients without and (D) AMH For each analysis the weights were standard- ‘dual diagnosis’ patients with addictions serv- ized by dividing by a constant (total number ice ‘dual diagnosis’ patients. had all patients been included ¸ total number Information was gathered on all persons actually sampled) which ensured that the who, on a specific day (15.01.97), were pa- total number of cases in each weighted analy- tients of any of the Trust’s services except in sis was equivalent to the total number of the case of its seven Community Mental cases actually studied and eligible to be in- Health Teams (CMHTs) whose 2612 pa- cluded (Lee et al., 1989). This technique tients were too many to study in total. A helps to ensure that realistic estimates of random sample of 60 patients of each CMHT standard error and results of hypothesis tests was selected from all those registered for the are obtained from the package (Norusis, Care Programme Approach (CPA) with that 1993). CMHT. Information was gathered from the Two sets of comparisons were made (see professional (‘key worker’) responsible for Design, C and D), each involving two groups co-ordinating the care of each patient using a and testing two similar hypotheses on each structured interview and standardized rating variable. To reduce the overall chance of scales. making a Type I error, for each variable a Several weeks in advance of being inter- Bonferroni adjusted significance level of viewed key workers were informed of the 0.025 was used. No further adjustment was nature of the project and told which patients made for the number of variables tested. 178 Nick Virgo et al. Means of normally distributed variables were 1996) for alcohol and other drugs separately. compared using the independent samples t- The scale is based on DSMIII-R definitions test. For variables measured on a nominal (American Psychiatric Association, 1987) scale, the groups were compared using the and has demonstrated high validity and reli- chi-squared test for association. If the vari- ability (Drake et al., 1989, 1990; Mueser et able could be ordered, the chi-squared test for al., 1995). Current status was determined by linear trend was used (Breslow & Day, 1980). the highest point of the scale occupied for a Researchers first established whether the period of one month or more during the patient had an SMI, either with or without a preceding six months (Drake et al., 1996). functional psychosis, according to the definition of the Department of Health’s Building Results Bridges report (Department of Health, 1996). This definition, which can include any Axis Prevalence of serious mental illness I disorder as an SMI depending on the pa- Key workers were interviewed about 1021 tient’s diagnosis and level of disability, vul- (87%) of the targeted 1177 patients. The nerability, risk and need for care, is broader numbers of patients investigated and cover- than the strict diagnoses of psychoses used as age rates N (%) were acute hospital, 98 an analogue of SMI in other studies (Menezes (100%), rehabilitation, 189 (98%), group et al., 1996; Duke, et al., 1994). Such therapy unit, 79 (69%), CMHTs, 342 (81% of inclusiveness combined with ease of applica- the target sample) and addictions, 313 (89%). tion made it better suited to this study of a full range of NHS care settings. Patients with Of the total 1021 patients, 55% (CI 52– current substance abuse or dependence and/ 58%) had a confirmed SMI and 44% (CI 41– 47%) had a confirmed SMI with functional or personality disorder were classified SMI only if they also met the criteria of a co- psychosis. Some 56% (CI 53–59%) had either or both of these and are henceforth morbid Axis I disorder. No further informa- described as the ‘SMI’ group. The preva- tion was collected for patients who did not lence of SMI with 95% CI are reported for meet the criteria for SMI. each part of the service in Table 1. The continued interview recorded psychiatric diagnoses, time in current treatment, Characteristics of the 510 SMI patients housing situation and employment status. On seven-point, ordinal scales for the previ- Because of missing data all of the follow- ous 6 months, key workers then rated the ing summaries are based on 500 patients, number of crises leading to additional inter- except for age, which is based on 496. vention; risk to self and others and risk of The mean age of the SMI patients was 42 abuse by others; overall level of disablement years (SD 12 range 17–67) and half (50%) resulting form mental illness; and need for were male. formal and informal care. The most commonly reported diagnoses Key workers then reported lifetime prob- were schizophrenia 52% (CI 48–56%); de- lems with alcohol or other drugs, the drugs pression 17% (CI 14–20%); bipolar disorder ‘misused’ during the previous 6 months, and 12% (CI 9–15%); schizo-affective disorder current status as either abstinence, non-prob- 10% (CI 8–13%); anxiety 7% (CI 5–10%); lematic use, abuse or dependence according obsessive-compulsive disorder 4% (CI 2– to the Clinician Rating Scale (Drake et al., 6%); personality disorder 2% (CI 1–4%); and Prevalence of substance misuse in SMI 179 Table 1: Point prevalence of (a) Serious Mental Illness (SMI) and (b) Co-occurring SMI and substance abuse or dependence (based on the preceding six months) in the Addictions Service and in each component of the Adult Mental Health (AMH) services Serious mental illness Co-occurring disorder Component of Service N % 95% CI N % 95% CI Addictions (n=313) 44 14 10–18 38 12 9–16 Acute Hospital (n=98) 66 67 58–77 27 28 19–37 Rehabilitation Service (n=189) 184 97 95–100 18 10 5–14 Group Therapy Unit (n =79) 1 1 0–4 0 0 0 CMHT1 A (n=55) 25 45 32–59 4 7 2–14 CMHT B (n=60) 45 75 64–86 13 22 11–32 CMHT C (n=46) 33 72 58–85 7 15 4–26 CMHT D (n=57) 24 42 29–55 4 7 2–15 CMHT E (n=29) 18 62 43–81 4 14 1–27 CMHT F (n=38) 28 74 59–88 3 8 0–17 CMHT G (n=57) 42 74 62–85 5 9 1–8 Total of CMHTs (n =342) 60 55–65 12 10–15 Total (n=1021) 56 53–59 12 10–14 1 Community Mental Health Team adjustment reaction 2% (CI 1–3%). The ment 5%, student 3%, sheltered employment majority had been in treatment for more than 3% and retirement 2%. 6 months. A third, (CI 29–37%) of SMI patients had The usual accommodations for SMI pa- in their lifetime abused or been dependent on tients had been their own home 34%, shel- alcohol or other drugs. Examining alcohol tered accommodation 18%, their parents’ and other drugs separately, 23% (CI 19– home 16%, privately rented accommodation 27%) had a lifetime history of abuse or de- 11%, local authority rented accommodation pendence on alcohol, while 22% (CI 18– 10%, an institution or hospital 6%, a bed sit 25%) had a lifetime history of abuse or de- 4% and lodgings 2%. pendence on other drugs. The Clinician The SMI patients main employment or Rating Scale measures of SMI patients’ cur- source of income had been disability benefit rent involvement with alcohol and other drugs, 46%, unemployment 27%, housewife 10%, based on the preceding 6 months, are summa- part-time employment 6%, full-time employ- rized in Table 2. Key workers reported that Table 2: Rating of current substance use, based on the preceding 6 months, in the (a) 510 Seriously Mentally Ill (SMI) patients and (b) the 123 who also had substance abuse or dependence (SMI+) Alcohol Drugs Alcohol or drugs SMI SMI+ SMI SMI+ SMI SMI+ Abstinent 73% 26% 81% 33% 66% - Non-problematic use 14% 16% 5% 4% 12% - Abuse 9% 42% 11% 50% 16% 74% Dependence 4% 16% 3% 13% 6% 26% 180 Nick Virgo et al. Table 3: Current problematic use (abuse or dependence) of alcohol and other drugs, based on the preceding 6 months, in the 510 seriously mentally ill (SMI) patients in each component of the services Service Problem with Problem with Problem with alcohol other drugs alcohol or other drugs % 95% CI % 95% CI % 95% CI Addictions n= 44 41 (26–56) 80 (67–92) 86 (76–97) Adult mental health n=4661 12 (9–15) 12 (9–15) 20 (17–24) Rehabilitation n=184 7 (3–11) 5 (2–9) 10 (5–14) Acute hospital n=66 21 (11–31) 33 (22–45) 41 (29–53) Community Mental Health Teams n=215 12 (8–17) 12 (7–16) 21 (15–26) Note: 1 The total includes one patient of the Group Therapy Unit most patients had abstained from both alco- have a problem with alcohol only, 42% with hol and other drug use, that most problematic other drugs only and a fifth, (21%), with both use was abuse rather than dependence and alcohol and other drugs. that there was little difference between levels In addition to completing Clinician Rating of problem use of alcohol and problem use of Scales for alcohol and other drugs, key work- other drugs. ers indicated from a checklist the drugs they believed each SMI patient had ‘misused’ in Prevalence of co-occurring serious the preceding 6 months. Half were reported mental illness and substance abuse or to have misused one drug only (including dependence alcohol), 34% two drugs, 4% three, 6% four Some 22% (CI 19–26%) of the 510 SMI and 5% five or more. Those most commonly patients were reported, on the basis of the reported were alcohol 74% (CI 65–81%); preceding 6 months, to have current abuse or cannabis 40% (CI 32–49%); prescription dependence on alcohol or other drugs and drugs 17% (CI 10–24%); amphetamines 12% thus a ‘dual diagnosis’. The proportions of (CI 6–18%); opiates 10% (CI 5–16%); those 510 SMI patients are reported sepa- benzodiazepines 10% (CI 4–15%); sedative- rately for alcohol and other drugs in different hypnotics 8% (CI 3–13%); over-the-counter parts of the Trust and are shown in Table 3. medications 2% (CI 0–5%); MDMA 3% (CI The prevalence of co-occurring problems in 0–6%); and LSD 2% (CI 0–6%). the total sample of 1021 patients was 12% (CI Comparisons between adult mental 10–14%) and those in different parts of the health severely mentally ill patients with Trust are summarized in Table 1. The preva- and without substance abuse or depend- lence in AMH was identical to that in the ence Addictions Service (12%). Patients with co-occurring problems tended Nature of substance problems in SMI to be younger (respective means 35.9 years v. patients with substance abuse or de- 43.9 years, t=5.9, df=440, p<0.0001) and pendence were more often male (65% v. 47%, c 2=8.4, Just over a third (37%) of the 123 patients df=1, p<0.01) and unemployed (40% v. 24%, with co-occurring problems were reported to c 2=8.1, df=1, p<0.01). Prevalence of substance misuse in SMI 181 Table 4: Diagnoses of SMI patients with and without current substance abuse or dependence based on the preceding 6 months AMH SMI AMH SMI Addiction SMI patients without patients with with substance substance misuse substance misuse misuse n=370 Contrast 1 n=85 n=38 Contrast 2 Schizophrenia 54% 52% 5% 8.7** Schizo-affective disorder 12% 6% 5% Bipolar disorder 11% 16% 5% Psychotic episodes 1% 2% 3% Depression 14% 23% 66% 9.2** Anxiety 7% 7% 29% Obsessive-compulsive disorder 5% 1% 11% Adjustment reaction 2% 2% 5% Anorexia nervosa 1% 2% 5% Paranoid ideas 0% 2% 3% Personality disorder 1% 7.7** 7% 5% Note: People with personality disorder were classified SMI only if there was a co-occurring Axis I disorder besides substance abuse or dependence. Contrast 1 compares AMH SMI patients who either had or did not have a substance abuse or dependence. Contrast 2 compares AMH SMI patients with a substance abuse or dependence against the same addictions service patients. Each contrast was computed using the c 2 test, and values of this statistic are only given when these are significant at the 0.025 level; ** p<0.01 Patients with co-occurring problems were other drugs (63% v. 37%, c 2=120.3, df=1, more likely to have lived with friends (7% v. p<0.00001). 1% c 2=10.0, df=1, p<0.01) or in privately By definition SMI patients with co-occur- rented accommodation (19% v. 8%, c 2=9.1, ring problems were more involved with alco- df=1, p<0.01) and less likely to have lived in hol or other drugs, the Clinician Rating Scale their own home (18% v. 39%, c 2=12.9, df=1, reflecting the most severe level of use for a p<0.001) in the preceding 6 months. period of 1 month during the preceding 6 Patients with co-occurring problems were (Table 5). For all SMI patients, key workers more likely to have more than one psychiatric also reported all those checklist drugs ‘mis- diagnosis besides substance abuse or depend- used’ in the preceding six months. Patients ence (15% v. 7%, c 2=5.1, df=1, p<0.025) and with co-occurring problems were more likely to have a personality disorder (7% v. 1%, to have ‘misused’ both alcohol (73% v 14%, c 2=7.7, df=1, p<0.01). Table 4 illustrates df) and cannabis (39% v 4%, df). Further c 2 diagnostic differences between groups of SMI tests were not performed because of small patients. numbers: the frequency of reports of ‘mis- Patients with co-occurring problems were use’ by patients without co-occurring prob- more likely to have reported a lifetime his- lems being less than 0.5% for each of the tory of abuse or dependence on alcohol (72% other drugs. The frequencies of ‘misuse’ of v. 10%, c 2 = 152.5, df = 1, p<0.00001) and/or other drugs by SMI AMH patients with co- 182 Nick Virgo et al. occurring problems were not significantly significant differences between the two groups different to those reported in the previous in either their housing (c 2=11.1, df=8, NS) or section (nature of substance problems) apart usual employment or source of income from opiates. (c 2=4.9, df=7, NS). The distribution of the number of crises The two groups did not differ significantly leading to more treatment according to key in their number of psychiatric diagnoses (c 2 workers reports on the ordinal scale was test for linear trend 2.6, df=1, NS) but addic- skewed, with 52% of patients having no tions patients were more likely than AMH crises in the preceding 6 months. However patients to be diagnosed with depression and those with co-occurring problems tended to less likely to be diagnosed with schizophre- have more crises (c 2 test for linear trend 18.9, nia (Table 4). There was no significant df=1, p<0.00001). The respective percent- difference between the two groups for time in ages of patients with and patients without co- current treatment (c 2 test for linear trend 4.7, occurring problems who had experienced the df=1, NS). following numbers of crises leading to addi- Abuse or dependence on alcohol or other tional treatment in the previous 6 months drugs were; none, 31%, 57%; one, 27%, 21%; The two groups did not differ significantly two,13%, 7%; three, 11%, 4%; four or more, in frequency of past abuse or dependence on 18%, 10%. either alcohol (c 2=0.6, df=1, NS) or other Key workers rated patients with co-occur- drugs (c 2=4.3, df=1, NS). However, com- ring problems at greater risk to themself than pared to AMH patients, addictions patients those without (c 2 test for linear trend 20.5, had significantly greater current involvement df=1, p<0.0001): and also at greater risk to in drugs (c 2 test for linear trend 16.3, df=1, the safety of others (c 2 test for linear trend p<0.0001) but not alcohol (c 2 test for linear 11.2, df=1, p<0.001). trend 0.0, df=1, NS), summarised in Table 5. Key workers’ ratings of patients’ current Addictions patients were more often reported levels of personal and social disability arising to be misusing more than one type of drug from their mental illness did not differ sig- (84% v. 44%, c 2=6.2, df=1, p<0.025) but nificantly between groups (c 2 test for linear there were higher rates of reported misuse of trend 1.6, df=1, NS). only one of the13 drugs considered: opiates Key workers’ ratings did not differ signifi- (62% v. 5%, c 2=33.8, df=1, p<0.0001). cantly between groups on either needing for- More addictions than AMH patients (90% mal (c 2 test for linear trend 2.4, df=1, NS) or v. 8%) were prescribed methadone (c 2=27.9, informal (c 2test for linear trend 4.3, df=1, NS) df=1, p<0.00001). care. Key workers judged whether or not patients recognised that they had both a mental Comparisons between those ‘dual illness and a substance misuse problem. A diagnosis’ patients served by the Adult significantly greater proportion of the addic- Mental Health Service and those served tions patients (84%) than AMH patients (37%) by the Addictions Service did so (c 2=9.1, df=1, p<0.01). The mean age for both groups was 36 The two groups did not differ significantly (t=0.2, df=115, NS). Males made up 65% of (c 2 test for linear trend 0.9, df=1, NS) on the AMH patients and 32% of the addictions crises leading to more treatment. patients (c 2=4.2, df=1, NS). There were no Key workers’ ratings did not differ signifi- Prevalence of substance misuse in SMI 183 Table 5: Current degree of involvement in alcohol or other drugs, based on the preceding 6 months, by groups of SMI patients AMH SMI without AMH SMI with Addiction SMI with substance misuse substance misuse substance misuse n=370 n=85 n=38 (a) Alcohol Abstinent 87% 26% 26% Non-problematic use 13% 14% 26% Abuse - 44% 24% Dependence - 16% 24% (b) Other drugs Abstinent 95% 36% 5% Non-problematic use 5% 5% 3% Abuse - 53% 21% Dependence - 6% 71% cantly between groups on either risk to self stance use problems were found in one in (c 2 test for linear trend 2.8, df=1, NS) or to eight of all patients using AMH services. The others (c 2 test for linear trend 2.4, df=1, NS). size of the sample allowed estimates of preva- Key workers’ ratings of level of risk of lence to be made with a reasonable degree of abuse by others were higher for Addictions confidence. than AMH patients (c 2 test for linear While these prevalence rates are lower than trend=12.7, df=1, p<0.001): the median (and those reported from some British and North inter quartile ranges) for the former was 5 (3) American studies they do represent a prob- and for the latter was 3 (2). lem of significant size. There are also simi- Ratings of patients’ current levels of per- larities between some of our results and some sonal and social disability arising from their of the other UK and US studies. Duke et al. mental illness did not differ significantly (1994) found that 22% of their community between groups (c 2 test for linear trend 4.8, sample had a lifetime history of alcohol abuse, df=1, NS) the present study found 23% in. Regier et al. Ratings did not differ significantly between (1990) found a 20% 6-month prevalence of groups in need for either formal or informal substance misuse in their community sub- care. sample drawn from mental health treatment settings, the present study found a 20% preva- Discussion lence in SMI AMH patients. Cantwell et al. (1999) found a 37% 12-month prevalence in Prevalence first-episode psychosis patients, the present Problematic use of mood altering substances study found 41% prevalence in AMI acute was found in one in five seriously mentally ill hospital patients. Menezes et al. (1996) found (SMI) patients using Adult Mental Health lifetime and 12-month prevalence rates that (AMH) Services within the previous 6 months. were higher than those from the correspond- One in three SMI patients had experienced ing SMI AMH group from the present study. problematic substance use in their lifetimes. That the prevalence of co-occurring disor- The co-occurring problems of SMI and sub- ders varied considerably within the care sys- 184 Nick Virgo et al. tem, from 10% of rehabilitation patients and dependence is rare, medical interventions 12% of CMHT patients to 28% of patients in (e.g. detoxification), and psychological treat- the acute hospital (and 41% of SMI patients ment approaches based on models of depend- there), to some extent represents the ways in ence (e.g. disease concept) may seem to be which patients are managed. For example largely inappropriate and therefore patients mentally ill patients who live in residential may be best treated in mental health rather rehabilitation facilities are more closely moni- than addictions services. tored than those living in the community and This is the first British study to examine the have less opportunity to purchase or ingest prevalence of co-occurring disorders in a illicit mood altering drugs. These figures specialist addictions service. It is interesting may also represent the ways in which the that this prevalence was identical to that misuse of drugs exacerbate mental illness observed in the specialist mental health serv- and make it more likely that substance SMI ices. That patients of addiction services patients using alcohol and other drugs will display high levels of psychopathology is not soon need an acute bed. Estimating the new but SMI is unexpected, especially given prevalence of co-occurring problems just by that most patients with a primary problem of investigating patients in acute wards would severe mental illness would be likely to present give an inflated estimate, reflecting Berkson’s at mental health services. It will be important fallacy (Berkson, 1949): estimates of the to investigate further the types of SMI ap- prevalence of co-occurrence are inflated when pearing in addiction services and the pathway studies examine samples from treatment serv- which led them in. ices rather than the general population (since Co-morbid patients have greater the probability that persons will receive treat- problems ment will be increased by either disorder). Berkson’s fallacy implies that the prevalence Patients with dual disorders tended to have of co-occurrence will be greater in services more extensive and more severe problems for acutely ill patients than in those providing than those without. Consistent with North longer term care. American studies this group posed more risks Most problematic substance use in patients to themselves and others, and more demands of the mental health services was abuse rather on services (in terms of crisis interventions), than dependence. It is not clear to what extent thus justifying concern about them. The abuse has the capacity to stimulate and exac- finding that they posed greater risk to others erbate mental illness, although some have is consistent with the British study that found argued from the stress-vulnerability perspec- higher levels of aggressive behaviour in the tive (Zubin & Spring, 1977) that patients with co-morbid group (Scott et al., 1998). The SMI are likely to experience adverse conse- interesting failure to find differences in key quences from ingesting relatively small workers’ ratings of need for formal and infor- amounts of mood altering substances. In a mal care, and disability arising from the men- recent review of the status of etiologic theo- tal illness was inconsistent with US research. ries of co-occurrence, Mueser et al. (1998) It is difficult to interpret the findings about concluded that there is support for this super- the association between personality disorder sensitivity model that implies that any use with substance use disorder, since personal- has the capacity to harm the health of se- ity disorders are probably not routinely diag- verely mentally ill persons. To the extent that nosed with the same rigour as Axis 1 disor-

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