comparison of response inhibition behavior between methadone maintenance patients and active opiate users

Background: increasing evidence indicates that opiate users and methadone maintenance patients (mmps) are impaired in executive control tasks and response inhibition behavior compared to healthy individuals; however, the cognitive functional difference between opiate addicts and mmps has not been clarified. objectives: this study employed go/no-go tasks to evaluate the response inhibition behavior in three groups: active opiate users, stable mmps and healthy control subjects with negative urine analysis. patients and methods: in this study, 45 opiate-dependents (including opium and heroin), 50 successful methadone maintenance patients (mmps) and 50 normal controls were recruited. these three groups were matched in terms of age, gender and education level. each subject conducted the six variants of go/no-go tasks in a sequential order, after being given the instructions to respond to stimulus displayed on the screen by pressing the space bar as quickly as possible (go stimuli) and withholding responses to other stimuli (no-go stimuli). we used mann-whitney nonparametric analysis to compare the performances of opiate users, mmps and healthy controls on go/no-go task scores. results: in go trials, opiate dependents and mmps showed better performance than controls with lower omission errors, while in no-go trials, opiate users and mmps committed more errors and revealed poorer performance than the controls. no significant difference was found between opiate users and mmps performance on go or no-go trials, and these groups were significantly faster than controls in response to targets on go trials or non-targets on no-go trials. conclusions: opiate users and mmps showed significant deficits on measures of response inhibition when compared to the normal participants, while mmps did not differ from opiate users in their ability to inhibit their response to non-targets.