HighlightsA broad range of domains of neuropsychological performance are significantly impaired in studies which have compared  methadone population s with the healthy controls .
However low power , poor quality and heterogenous population s limit the interpretation of these results .Short term ( less than 1 year ) abstinent groups , when compared with methadone groups , still exhibited cognitive impairments but results are inconclusive .
It is still not clear what the role of global sedative effects of opioids such as methadone have on cognitive impairment .
Only higher quality longitudinal studies using ecologically valid cognitive tests , in well‐defined population groups can address this question .Methadone population s present with a broad range of neuropsychological impairment when compared with healthy controls .
Results : Data from a total cohort of 1063 CM , 412 AP and 879 HP participants , from 23 independent studies  indicate global impairments in neurocognitive function in CM relative to HP participants .
Conclusion : Method ological issues such as small sample sizes , heterogeneity and poor quality limited the interpretation of the results and does not address whether the observed impairments reflect co‐morbid functioning , methadone‐related sedation and /or other factors .
Introduction : There is a presumption that neurocognition is commonly impaired in chronic methadone exposed individuals ( CM ) when compared with healthy controls ( HP ) .
Additionally , it remains unclear if short term ( < 1 year ) abstinence ( AP ) is associated with an altered cognitive profile when compared with CM .
Impaired performance in a test of decision-making by opiate-dependent tobacco smokers.
This study tested whether opiate dependence , tobacco smoking , or their combination accompanied impaired performance on the  gambling task ( GT )  , which tests decision-making .  GT previously detected impairments in patients with lesions of the ventromedial prefrontal cortex and in substance abusers . Four groups were matched on demographic characteristics and intelligence : methadone-maintained smokers ( n = 9 ) and nonsmokers ( n = 9 ) , and control ( i.e. , not opiate-dependent ) smokers ( n = 9 ) and nonsmokers ( n = 10 ) . The  Wisconsin Card Sorting Task ( WCST )  was administered to test whether differences in  GT performance reflected generalized deficits in prefrontal cortical function . While there were no significant group differences on the WCST , groups differed significantly on  GT performance ( F(3,31 ) = 2.95 , P = 0.048 ) , controlling for depressive symptom ratings and childhood attention deficit hyperactivity disorder .  Methadone-maintained smokers ( but not nonsmokers ) performed more poorly than either of the two control groups ( P = 0.007 versus smokers ; P = 0.024 versus nonsmokers ) . In a planned analysis of methadone-maintained subjects , smokers scored more poorly on  GT  than nonsmokers ( F(1,18 ) = 5.64 , P = 0.032 ) and had more treatment failures ( 67 % heroin use during the last 30 days versus 20 % ) . The findings suggest that among opiate-dependent individuals , tobacco smoking may be a marker for a more severe form of substance abuse disorder , reflecting impaired decision-making , as modeled by GT
HighlightsA broad range of domains of neuropsychological performance are significantly impaired in studies which have compared  methadone population s with the healthy controls .
However low power , poor quality and heterogenous population s limit the interpretation of these results .Short term ( less than 1 year ) abstinent groups , when compared with methadone groups , still exhibited cognitive impairments but results are inconclusive .
It is still not clear what the role of global sedative effects of opioids such as methadone have on cognitive impairment .
Only higher quality longitudinal studies using ecologically valid cognitive tests , in well‐defined population groups can address this question .Methadone population s present with a broad range of neuropsychological impairment when compared with healthy controls .
Results : Data from a total cohort of 1063 CM , 412 AP and 879 HP participants , from 23 independent studies  indicate global impairments in neurocognitive function in CM relative to HP participants .
Conclusion : Method ological issues such as small sample sizes , heterogeneity and poor quality limited the interpretation of the results and does not address whether the observed impairments reflect co‐morbid functioning , methadone‐related sedation and /or other factors .
Introduction : There is a presumption that neurocognition is commonly impaired in chronic methadone exposed individuals ( CM ) when compared with healthy controls ( HP ) .
Additionally , it remains unclear if short term ( < 1 year ) abstinence ( AP ) is associated with an altered cognitive profile when compared with CM .