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 .
Cognitive Functioning During Methadone and Buprenorphine Treatment: Results of a Randomized Clinical Trial
Cognitive impairment in drug-dependent patients receiving methadone ( MMP ) maintenance treatment has been reported previously . We assessed cognitive functioning after at least 14 days of stable substitution treatment with buprenorphine ( BUP ) or MMP and after 8 to 10 weeks . We performed a r and omized , nonblinded clinical trial in 59 drug-dependent patients receiving either BUP or MMP maintenance treatment and healthy normal controls ( n = 24 ) matched for sex , age , and educational level . Thirteen patients dropped out of the study before the second testing was performed  ( BUP , n = 22 ; MMP , n = 24 ) . A neuropsychological test battery was used to measure selective attention , verbal memory , motor/cognitive speed , and cognitive flexibility . In addition , subjective perceived stress was assessed with a question naire . Patients in both treatment groups performed equally well in all of the cognitive domains tested . Both BUP and MMP patients showed significantly improved concentration and executive functions after 8 to 10 weeks of stable substitution treatment . The control group achieved better results than the BUP and MMP groups in most cognitive domains , indicating cognitive impairment in the patients . Perceived stress did not show any significant change after 8 to 10 weeks of treatment , and no major differences were detected between the 3 groups . No effects of perceived stress on cognitive function were found . Our results indicate a cognitive impairment in patients receiving maintenance treatment with BUP  or  MMP  compared with healthy controls . Selective attention improved in both patient groups during treatment . We propose that the improvement of attention may facilitate rehabilitation of drug-dependent patients
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 .