Cognitive impairment in methadone maintenance patients

Abstract

Few well-controlled studies have examined psychomotor and cognitive performance in methadone maintenance patients (MMP). In the present study, performance of 18 opioid-dependent MMP was evaluated relative to that of 21 control participants without substance abuse histories. The MMP and control groups were balanced with respect to gender, race, age, years of education, current employment status, current reading level, and estimated IQ score. Recent drug abstinence was verified by urine testing. Participants with a urine screen positive for benzodiazepines or a breathalyzer test positive for alcohol prior to performance testing were excluded. To avoid testing under conditions of acute heroin or cocaine intoxication, but without testing under conditions of acute withdrawal, participants with current use of heroin or cocaine were only required to abstain for 24 h prior to performance testing. MMP exhibited impairment relative to controls in psychomotor speed (digit symbol substitution and trail-making tests), working memory (two-back task), decision making (gambling task), and metamemory (confidence ratings on a recognition memory test); results also suggested possible impairment in inhibitory mechanisms (Stroop color-word paradigm). MMP did not exhibit impairment in time estimation, conceptual flexibility or long-term memory. The wide range of impaired functions is striking, and may have important implications for daily functioning in MMP. Further research is necessary to determine the clinical significance of the impairments in laboratory-based tests for daily performance in the natural environment, as well as to differentiate impairments due to acute methadone dosing, chronic methadone maintenance, chronic poly-drug abuse, and other factors.