The prevalence rates for lifetime alcohol and cannabis use among the FEP sample were similar to those of the Canadian population. A study by Barnes et al8
showed that the prevalence rate of lifetime cannabis use in a clinic sample of patients with FEP was 64.0%, which was consistent with the results of our study. However, other clinic studies report high prevalence rates of cannabis abuse among FEP participants in comparison to the general population, but these studies, which include the one by Barnes et al,8
do not compare the prevalence rates of lifetime cannabis use among FEP participants to controls from the same age-group.2,43
The higher prevalence rates for lifetime hallucinogen and cocaine use shown in our FEP sample compared with the general population warrants further scrutiny. Hallucinogen and cocaine use are considered to be risk factors for psychosis in vulnerable people. In healthy individuals, hallucinogen use produces a range of symptoms similar to schizophrenia.44
Hallucinogens also produce changes in the rodent brain believed to reflect changes found in schizophrenia.45
Hallucinogen use in vulnerable people may sensitize the neuronal systems to hallucinations.45
Cocaine can trigger brief psychotic episodes, which are more common among those cocaine users who have a familial loading for schizophrenia.46
Our findings are consistent with this evidence linking hallucinogen and cocaine use to psychosis and suggest that more studies are needed that focus upon hallucinogen and cocaine use in FEP.
Our findings suggest that there are more participants with FEP who engage in high-risk patterns of substance use than participants who meet criteria for DSM-IV
The discrepancies between the SCID diagnoses of abuse and the various measures of use reflect the inherent differences in the criteria used to define abuse. The SCID diagnoses are based upon DSM-IV
criteria and require evidence of clinically significant impairment. The AUDIT and the DAST, on the other hand, recognize hazardous patterns of substance use, which may or may not reflect clinically significant impairment.30
The results suggest that EI services have an effect on subthreshold cases in terms of DSM-IV
criteria; the subthreshold cases would include those participants meeting criteria for drug abuse or hazardous alcohol use. Interestingly, the participants who were heavy drinkers did not respond to the EI treatment, but heavy drinking is strictly a reflection of quantity consumed. Clinical consequences may not be evident. Research is needed to determine whether more specific interventions, such as cognitive behavioral therapy or motivational interviewing,47
are effective for the heavy drinking group.
While involuntary hospitalizations and arrests decreased significantly among all the participants, the disparity between substance abusers and nonabusers observed at baseline diminished significantly at 12 months. Over the 12 months of treatment, the prevalence of substance abuse decreased significantly for all groups, with the exception of the group meeting criteria for heavy drinking. These findings provide some evidence for the effectiveness of EI services for substance abuse among FEP populations.
However, this evidence is preliminary. Although, the results of this study are generalizable to clinic samples of patients, the results may not be generalizable to the overall population of individuals with FEP because this study did not use an epidemiological sample. The study design has a number of key limitations: the design was not randomized with a control group; at 12 months the prevalence of substance abuse and dependence was not determined using the SCID; and the 12-month follow-up period was relatively short, given the long-term course of the illness and the long-term impact of substance abuse. Full data sets were available for only 65% of the sample. Our study failed to compare the prevalence rates of cannabis abuse among participants compared with the general population. Furthermore, our study did not assess the frequency of cannabis use (for example daily or weekly use)—an important omission in light of studies that suggest a causal relationship between weekly cannabis use in adolescence and the later development of psychosis.9–11,48
The CAS relied upon telephone interviews, a method which may tend to overrepresent individuals who are married or who have some postsecondary education training.30
The 2 very different methodologies used to collect data for our clinical sample (face-to-face interview) vs the CAS population sample (telephone survey) may have influenced the results for such a sensitive topic as alcohol or drug use. Although there are no studies that compare the effects of social desirability bias upon population survey interviews vs interviews conducted in a clinical context, comparisons of telephone vs face-to-face survey interviews do not consistently point to a bias arising from the survey method.49
We recognize the limitation in using the CAS database because of the low response rate (47.0%). However, similar analyses were also undertaken with data derived from a different Canadian population survey (the Canadian Community Health Survey, version 1.2: Mental Health and Well-being50
), a survey that obtained a better response rate (77.0%). The analyses from the Canadian Community Health Survey yielded similar findings on the few key comparisons that were possible using the present clinical sample (for example, 54.4% lifetime cannabis use).
Despite these limitations, the results reported here are likely to add to our knowledge regarding the problem of substance abuse in FEP. To the best of our knowledge, there are currently no studies that have compared the prevalence rates of substance use from clinic samples of FEP patients with age-adjusted samples from the general population. Few studies have addressed the effects of an EI service over time on substance use or abuse4,5,51
among participants with FEP. Only 1 randomized controlled trial has demonstrated effectiveness of EI services on substance abuse.25
Substance abuse among patients with FEP may be more amenable to treatment than substance abuse among patients with more chronic forms of the disorder. EI services have the potential to detect hazardous substance use in a population vulnerable to addiction before their use leads to more serious impairment. Therefore, EI in psychosis warrants further research and is a promising therapeutic approach, not only for treating psychosis but also for detecting and reducing substance abuse among individuals experiencing a first episode of psychosis.