Under-Reporting of Drug Use Among Individuals With Schizophrenia: Prevalence and Predictors

Background and Purpose: Drug use is common in schizophrenia, and it is suspected that many individuals with this condition under-report their use, leading to significant barriers to treatment.  There is a consensus that multi-method approaches to drug use assessment relying on all available evidence are ideal, yet most studies and community-based practices employ measures that exclusively consider what individuals with schizophrenia disclose about their use. Few studies have evaluated the measures that consider what these individuals disclose about their illicit behaviors, which could have implications for drug use assessment and the treatment of this population. This study examined the rates of drug use disclosure in a large, heterogeneous sample of individuals with schizophrenia, when compared with laboratory assays, and identified characteristics that predict drug use under-reporting.  

Method: A total of 1042 individuals with a schizophrenia diagnosis participating in the screening/baseline procedures of the Clinical Antipsychotic Trials of Intervention Effectiveness study completed a self-report of their drug use and laboratory tests, which assayed cannabis, cocaine and methamphetamine; procedures included radioimmunoassay (RIA) and urine drug screens. The analytic approach examined (1) the concordance between laboratory tests and the self-report of drug use and (2) the predictors of drug use under-reporting in this sample.  

Results: More than one third (n = 397; 38.0%) of the 1042 participants tested positive for any drug use, and cannabis yielded the largest number of positives (n = 280; 26.9%), followed by cocaine (n = 213; 20.4%), and methamphetamine (n = 72; 6.9%) by laboratory tests. Of the 397 participants with positive results, most (n = 229; 57.7%) did not disclose using drugs on the self-report, and the sensitivity of this measure was low for any drugs, cocaine, cannabis and methamphetamine (.42, .32, .38, .26, respectively). Then, logistic models were employed to examine the predictors of this under-reporting, controlling for age, race and gender. Greater criminal justice system involvement significantly predicted accurate reports of drug use for those with positive results for any drugs and cannabis (all p < .050), whereas illness severity and psychopathology did not predict drug use disclosure (all p > .955). Greater neurocognitive impairment was the most consistent predictor of under-reported drug use for participants with positive results for any drugs, cannabis and cocaine (all p < .025), and those with better ( > 1 SD) cognitive function were 1.55 times more likely to accurately report their use.

Conclusions and Implications: The clinical relevance of this research is underscored by the fact that this is the first study to examine the predictors of under-reported drug use in schizophrenia, and the findings show under-reporting is considerable when compared to laboratory assays. Participants under-reporting drug use were more likely to manifest neurocognitive deficits, and the exclusive reliance on self-reports should be used with caution when social workers are engaging individuals with schizophrenia into treatments for addiction.  It will be imperative that social workers secure an integral role in future research development efforts seeking to minimize cognitive impairments in this population, and thereby focus on optimizing treatment.