Cognitive functioning and cognitive style among drug users in maintenance substitution treatment

While there is a substantial literature showing significant benefits associated with maintenance treatments, there is recent evidence that methadone prescribing may be associated with deficits in cognitive functioning, particularly around executive function. This study assessed levels of cognitive function using the Wechsler Adult Intelligence Scale and linked clients scores on this measure to aspects of cognitive style and to current drug use and drug history. A sample of 30 problem drug users attending two Birmingham community drug services was recruited opportunistically. The mean intelligence quotient (IQ) of the participants was 84.4, 15.6 points lower than the UK average, with participants reporting much lower Verbal than Performance IQ. A significant negative association was found between prescribed methadone dose and IQ. There were no correlations between IQ and criminal thinking or impulsivity. There are concerning implications for the delivery of structured psychosocial interventions to clients with such depressed cognitive functioning, and the association between higher dose and lower IQ merits further investigation.