The association between substance misuse and first-episode psychosis in a defined UK geographical area during the 1990s
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- Donoghue, K., Medley, I., Brewin, J. et al. Soc Psychiatry Psychiatr Epidemiol (2011) 46: 137. doi:10.1007/s00127-009-0175-5
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The aim of this study was to examine the prevalence of all substance use disorders (SUD) and cannabis-specific SUDs reported in two first-episode epidemiological studies, conducted in the same catchment area, 5 years apart.
The prevalence of schizophrenia in Nottingham and Aetiology and Ethnicity of Schizophrenia and Other Psychoses studies included all people with a first-episode of psychosis between 1992 and 1994 and 1997 and 1999, respectively. Those individuals with a comorbid diagnosis of a SUD (ICD-10 harmful use or dependence) were identified.
An upward (but not statistically significant) trend in all SUDs was found for the first-episode study population as a whole, between the two cohorts (11.9–18.2%). When analysed by age, a significant increase in cannabis-specific SUDs was observed for all first-episode cases aged 16–29 between cohorts (3.2–10.6%). When analysed by age and gender, a significant increase in all SUDs was apparent for female first-episode patients aged 16–29 between cohorts (6.1–24.2%), this same increase was not seen in male patients.
Illegal drug misuse is common in patients with a first-episode of psychosis. However, most concerning is that when both age and gender are considered, females with a first-episode of psychosis aged 16–29 show a highly significant rise in the prevalence of all SUDs over the 1990s. More recent drug use data from England and Wales shows that the prevalence of drug use in the 21st century is declining; further epidemiological studies are required to determine whether this is also the case in young female first-episode psychosis populations.
A comorbid substance use disorder (SUD) is a poor prognostic factor in psychotic illness, associated with more hospitalisations , treatment non-compliance  and higher relapse rates . The prevalence of SUDs in patients diagnosed with a psychotic illness has been reported as more frequent than that of the general population [4–7] with prevalence rates varying depending on service setting, geographical area and social context . Despite the high prevalence and detrimental effect of SUDs on the course of psychotic illness, there have been few large, epidemiological studies conducted to objectively assess the extent and pattern of comorbidity at the first-episode of psychosis. A recent review  identified just seven such studies with prevalence rates ranging from 6 to 44% with SUDs being most common in young males. However, it remains unknown if the prevalence rates of SUDs in psychoses are changing from year to year in line with the changing patterns of SUDs in the general population. This is of particular interest given the postulated association between cannabis use and increased risk of psychosis . One speculative paper using projection calculations, has suggested that increasing cannabis use per se could account for 25% of all new cases of schizophrenia by 2010, representing an overall increase in schizophrenia of 29% compared to 1990 .
Uniquely, there have been two epidemiological studies of first-episode psychosis conducted in the same defined catchment area of Nottingham, UK, using similar methodology at contiguous points in time. These were the Schizophrenia in Nottingham (SIN) study conducted between 1992 and 1994  and the Aetiology and Ethnicity of Schizophrenia and Other Psychoses (ÆSOP) study conducted between 1997 and 1999 .
This study therefore aims to examine the prevalence of all SUDs and cannabis-specific SUDs (harmful use or dependence of cannabis only) in the SIN and ÆSOP first-episode psychosis studies. It is hypothesised that there will be a significant rise in the prevalence of overall SUDs and specifically in cannabis SUDs for younger males between the SIN and ÆSOP study cohorts.
Both SIN (1992–1994) and ÆSOP (1997–1999) were epidemiologically based studies that identified potential cases presenting to psychiatric services over a 2-year period with a first-episode of psychosis, using the World Health Organization psychosis screen . The common inclusion criteria were (1) aged 16–64, (2) resident in the defined catchment area, Nottingham, (3) no previous contact with services with psychotic symptoms, (4) the presence of delusions, hallucinations, thought disorder, bizarre or psychotic behaviour that may indicate a psychotic illness, (5) the absence of an organic cause resulting from cerebral atrophy/injury (ICD-10 code F00-F09 ) or severe learning disability. There was regular liaison between the research study teams and all points of secondary mental health service contact to identify all cases of first-episode psychosis. A ‘leakage’ study was also conducted, based on the methodology of Cooper et al.  to identify any potential cases missed by the original screening process. All electronic and paper information systems within the mental healthcare system were scrutinised to identify patients with a first-episode of psychosis. Case notes were then reviewed and clinical staff interviewed. Patients meeting inclusion criteria were entered into the study.
An extensive battery of assessments was administered to consenting participants. These included; the Schedules for clinical assessment in neuropsychiatry (SCAN) , schedule for the assessment of negative symptoms  and the personal and psychiatric history schedule . If participants declined a face to face interview, the SCAN Item Group Checklist (IGC)  was completed from case notes and information from clinical staff. Following clinical data collection, a consensus diagnostic meeting was held for each case, a vignette which summarised the presenting complaint was presented, in addition to clinical information from the SCAN or IGC to a group of clinicians blind to patient identity. Consensus meetings were attended, where possible, by the principle investigator and clinical researcher who conducted the assessments. A primary diagnosis of a psychotic disorder (ICD-10 codes F1X-F33 ) was assigned, as well as a comorbid diagnosis of substance harmful use (ICD-10 F1X.1) or dependence (ICD-10 F1X.2) where appropriate.
Ethical approval was obtained from the local research ethics committee for both the SIN and ÆSOP studies. Further details on entry criteria and study design for SIN and ÆSOP are presented elsewhere [12, 13, 20].
Characteristics of the sample
Sociodemographic and diagnostic characteristics for the SIN and ÆSOP studies
SIN (N = 168)
ÆSOP (N = 203)
SUD aged 16–64
Prevalence of all SUDs overall and cannabis-specific SUDs for the SIN and ÆSOP studies and Chi-squared analysis for those aged 16–64
SIN % (N)
ÆSOP % (N)
Similarly in the ÆSOP study, the majority of those with a comorbid SUD were male (78.4%, 29/37) with a mean age of 23 (SD 5.5). The prevalence of cannabis-specific SUDs in the ÆSOP study was 6.9% (14/209) poly-drug use 7.9% (16/203), and stimulant use 3.4% (7/203).
There was a difference of 6.3% for all SUDs and 2.7% for cannabis-specific SUDs between the SIN and ÆSOP studies, but these differences did not reach statistical significance (p > 0.05).
Comorbid SUDs were more common in males in both SIN (χ2 (1) = 5.902, p = 0.015) and ÆSOP (χ2 (1) = 6.623, p = 0.010) studies. Males and females were subsequently analysed separately. An increase in the prevalence of all SUDs between the SIN and the ÆSOP studies for both males and females was found, but this difference did not reach significance (p < 0.05). A similar result was found for cannabis-specific SUDs, with an increase in prevalence between the two male psychosis cohorts that did not reach significance at the p < 0.05 level. Unfortunately, numbers were insufficient to conduct a separate analysis for females.
SUD, participants aged 16–29
In the SIN cohort, the prevalence of SUDs for participants aged 16–29 was 14.9% (14/94) when compared with 5.8% (5/74) for those aged 30 and over. This difference was not statistically significant (χ2 (1) = 2.733, p = 0.098). However, in the ÆSOP cohort those aged 16–29 had a significantly higher prevalence of SUDs (30.1%, 34/113) when compared with those aged 30 and over (3.3%, 3/90), χ2 (1) = 24.061, p < 0.001).
Prevalence of all SUDs overall and cannabis-specific SUDs for the SIN and ÆSOP studies and Chi-squared analysis for those aged 16–29
SIN % (N)
ÆSOP % (N)
Post hoc power analysis
Post hoc power analysis was conducted in order to further investigate the non-significant increase in the prevalence of SUDs in those aged 16–64, the results of which are presented in Table 2. Statistical power was low for this analysis ranging from 0.217 to 0.465.
Power analysis was also conducted post hoc for the χ2 comparisons for those aged 16–29. Statistical power was higher for this analysis ranging from 0.430 to 0.716 (Table 3).
A higher SUD prevalence rate in younger males was found in this study, which has been replicated in other epidemiological first-episode psychosis studies [9, 24]. The prevalence rates of SUDs found in the SIN and ÆSOP studies are similar to rates reported in Germany, 14% ; however, higher prevalence rates have been reported in Canada, 34.5%  the USA, 27%  and Scandinavia, 23% . This also reflects the contemporaneous pattern of drug use in the general population of England and Wales as reported by the British Crime Survey (BCS) . The BCS is a household survey conducted biannually and is completed by around 10,000 people across England and Wales living in both urban and inner-city areas. Those taking part are asked if they have taken a list of illicit substances ever, in the past year or in the past month, therefore this information only refers to the number of people that had used a substance, with no quantitative or diagnostic rating attached to them. Although quantities and frequencies of drug taking is not recorded this data is the best available in terms of drug use rates in England and Wales and can be used as a guide to the general pattern of use.
Comparative rates of drug use between cohorts
The increase in the comorbid prevalence rate of all SUDs in the two cohorts did not reach significance (p > 0.05) for participants aged 16–64. Statistical power was low as a result of a small sample size, despite having recruited large numbers of first-episode patients.
A significant increase in all comorbid SUDs was observed when comparing the 16–29 year age group alone across the cohorts. This increase is quite striking given the small 2% increase in rates of substance use in the general population of England and Wales, reported as part of the BCS, over the same time period . When split by gender and age, a significant rise in the prevalence of comorbid cannabis-specific SUDs and a trend for all SUDs was observed between the SIN and ÆSOP cohorts for younger males. This is consistent with the increase in cannabis use (25–29%) and overall drug use (28–33%) in young males seen contemporaneously in the general population.
However, the significant rise in all comorbid SUDs apparent between the SIN and ÆSOP cohorts amongst females aged 16-29, was not observed in the general population, where a static 19% prevalence rate was reported between 1994 and 1998 . This may indicate that the traditional gender differential, with regards to comorbid substance abuse and psychosis in the UK, is changing as the prevalence of all comorbid SUDs in younger women with psychoses appeared to be on the increase in the 1990s in UK.
Whilst these results should be treated as preliminary due to the aforementioned small sample size, it is evident that although SUDs are more prevalent in male patients with a first-episode of psychosis, female patients must not be forgotten when considering prevention, intervention and treatment of SUDs.
The increase in SUDs in the 16–29 age group is of concern due to the possible undesirable effects on a patient’s course and outcome of illness [2, 3, 29]. The presence of a comorbid SUD in patients with psychoses has already been identified as being associated with a significant increase in utilisation and cost to inpatient mental healthcare service providers . Furthermore, the same study commented that a previous SUD may also lead to a greater cost to a socialised healthcare system (as in the UK) in terms of housing support and psychosocial support of patients, over a longer period of time.
Cannabis and first-episode psychosis
The increase in comorbid cannabis-specific SUDs across the two cohorts in this study is of particular interest due to the controversial nature of the relationship between cannabis use and psychosis. Historical  and birth cohort studies [32, 33] have both found cannabis usage to precede psychotic symptom onset. There has also been a growing body of evidence to suggest an association between cannabis use and heightened risk of a psychotic illness, with heavier use posing an even greater risk . The dose–response effect is particularly important due to the escalation in potency of the drug and the development of more sophisticated, indoor, hydroponic growing techniques introduced in England in the early 1990s [34, 35].
Recent trends in UK drug usage
The most recent drug use data for England and Wales suggests that there has been a decrease in overall drug use in the population from 12.1% in 1998 to 9.3% in 2007/08 and a steady decrease in cannabis use from 10.3 to 7.4% . The same has been reported for those aged 16–24 with overall drug use rates falling from 31.8% in 1998 to 21.3% in 2007/08 and for cannabis from 28.2 to 17.9%. This pattern of decrease in overall drug use can be seen for all three younger age groups reported in the BCS (i.e. those aged 16–19, 20–24 and 25–29). Further epidemiological studies are needed to determine whether this decrease in drug use prevalence is mirrored in those with a first-episode of psychosis, especially amongst women.
Strengths and limitations of this study
This study had a number of strengths. It is a comparison of two large, epidemiological studies, conducted in the same catchment area using the same methodology, 5 years apart. Diagnoses were assigned to participants using ICD-10 criteria following consensus meetings where all available information was collated and presented. Also, a leakage study was performed to identify any patients that may have been missed by the original screening process.
A limitation of this study is the lack of corroboration of self-report of drug use with the use of biological techniques such as hair or urine analyses. Previous studies have shown self-reporting of drug use to be reliable and consistent with urine drug screens in cannabis users  and patients with schizophrenia . However, diagnoses of SUDs in the SIN and ÆSOP studies were derived through consensus meetings utilising all available information, reducing any potential confounding factors between the two studies. Finally, the sample size of participants with a SUD is relatively small; a lack of statistical power may therefore have increased the chance of a type two error.
There has been considerable interest and concern about the possible impact of cannabis use both in the incidence of new cases of schizophrenia and as a poor prognostic factor in comorbid cases. This paper suggests that there has been an increase in drug taking in the 16–29 age group, especially amongst women, between the SIN and ÆSOP study populations. The contemporaneous pattern of drug use in the indigenous population mirrors this for men, but not for women. Recent drug use data from England and Wales now shows that the prevalence of drug use is declining; further epidemiological studies are required to determine whether this is the case in first-episode psychosis populations.