Substance misuse has been proven to have many negative academic, behavioral, and emotional effects. Individuals who are addicted to alcohol, opiates, cocaine, or cannabis have been studied at length in an effort to demonstrate the deleterious consequences of substance use on users, family members, friends, employers, and society at large. But less is known about how substance use affects cognitive abilities of individuals with psychotic disorders. This is a critical area of research, as substance use rates are particularly high in individuals with psychosis, especially people with schizophrenia. Kim Donoghue of the Division of Psychiatry at the University of Nottingham in England recently conducted a meta-analysis of existing research on substance and poly-substance use among individuals diagnosed with psychosis.
Donoghue reviewed numerous studies that included people with psychosis who had a history of substance use, misuse, and dependency related to alcohol, cannabis, and cocaine. The literature also included participants with psychosis who had no history of substance use. Donoghue analyzed how each level of use and each particular substance affected cognitive functioning and found that in contrast to what was expected, individuals with psychosis who used drugs performed better on some cognitive tests than those who did not use drugs. Specifically, cocaine users had better psychomotor processing speed and attention than nonusers, but had deficits in memory and verbal ability. Individuals with psychosis who used cannabis had better overall functioning than those who did not use cannabis.
The findings revealed here should be considered with caution. First, Donoghue acknowledges that the effect sizes in her study were small. The limited number of studies focusing on unique substance use with psychosis limited the scope of the results. Also, Donoghue points out that the differentiation between use, misuse, and dependency varied between studies. One explanation for the finding related to cannabis is that it is theorized that these individuals may be higher-functioning individuals. If they are able to seek out and acquire drugs, despite the limitations of their psychosis, they may have higher functional competence and more neurological capacity than their nonusing peers. However, this finding should not be considered advocacy for drug use. Donoghue added, “Longitudinal studies with a more extensive follow-up period will enable an in-depth assessment of the extent of impairment resulting from long-term substance misuse.”
Donoghue, Kim, and Gillian A. Doody. Effect of illegal substance use on cognitive function in individuals with a psychotic disorder, a review and meta-analysis. Neuropsychology 26.6 (2012): 785-801. Print.
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