Medication non-adherence presents a considerable problem in patients with schizophrenia. Cognitive and executive functions can affect adherence. The association between medication non-adherence and cognitive impairment in schizophrenia is under investigated with limited and conflicting research data.

To prospectively assess the rate of drug adherence among a sample of patients with schizophrenia and to compare the cognitive and executive functions between adherent and non-adherent patients.

One hundred and nine patients with schizophrenia diagnosed according to the DSM-IV classification were initially assessed by the Wechsler Adult Intelligence Scale (WAIS), Wechsler Memory Scale-Revised (WMS-R) and Wisconsin Card Sorting Test (WCST) and six months later by the Brief Adherence Rating Scale (BARS).

Among the patients, 68.8% were non-adherent to their antipsychotic medication. Adherent patients (31.2%) had significantly higher mean scores for the total, verbal and performance IQ. Moreover, they had significantly higher mean scores in most of WMS subtests (orientation, information, verbal paired association, digit span, visual memory span), and higher mean scores for; total correct, conceptual level response, percentage and categories completed on the WSCT subscales (P<0.0001). Whereas the non-adherent group had higher mean scores in; trials administered, total errors, perseverative responses, and perseverative errors (P<0.0001). In a step regression analysis, digit span, conceptualization, total and percentage of errors were putative predictors of non-adherence to antipsychotic medications.

Cognitive deficits, especially verbal memory and executive functions were the strongest patients’ related factors associated with non-adherence to medication. Psychiatrists should consider possible cognitive factors influencing adherence to enable offering proper interventions.