Methadone has been used to treat opiate dependence since the mid-1960s. Despite its clinical effectiveness there is evidence from neuropsychological studies demonstrating that its long-term use might have negative effects on cognition. Nevertheless, it remains uncertain whether the observed cognitive impairments in patients undertaking methadone maintenance treatment (MMT) are solely attributable to the pharmacological effects of methadone, as suggested by some researchers. Determining the effects of MMT on neuropsychological function using electroencephalography (EEG) combined with event-related potentials (ERP) has been used infrequently. However EEG and ERP provide a means of closely examining information processing to determine whether MMT induces any deficits. The purpose of this review was to investigate whether psychophysiological evidence supports cognitive impairment in association with MMT by focusing on research using EEG and ERPs. The findings of EEG studies to date appear not support the notion that cognitive impairments are attributable to the specific pharmacological effects of methadone suggested by some neuropsychological studies. However, due to the methodological deficits and limited number of the studies, any conclusion based on the findings of the existing EEG studies should be avoided.
Keywords: EEG; ERP; Methadone; Opiates; Review.