Hot and cold executive functions in pure opioid users undergoing methadone maintenance treatment: Effects of methadone dose, treatment duration, and time between last methadone administration and testing

Context: Methadone maintenance is a standard treatment for opiate-dependent individuals. However, deficits in cognitive functioning have been associated with this treatment. Aim: This study aimed to determine the dose and treatment duration-related effects of methadone on executive functions. Setting and Design: Pure male opioid users with no considerable history of other drug abuse, undergoing methadone maintenance treatment (MMT) were recruited from a major government-run de-addiction center. Methods: Hot executive functions including decision-making and emotion recognition were assessed using the Iowa gambling task and Ekman faces test, whereas cold executive functions including working memory (WM), cognitive flexibility, and response inhibition were assessed using n-back, Wisconsin card sorting test, and the GO/NOGO task, respectively. Statistical Analyses Used: Descriptive statistics, Pearson's correlation coefficients, and multiple regression analysis were used to test the hypotheses of the study. Results: Methadone dose and length of MMT were found to be associated with greater impairment in executive functions. Impairment in cognitive performance was also found to be inversely related to time since dosing. Regression analyses revealed that methadone dosage and time since dosing accounted for a significant proportion of the variance in cognitive flexibility, while the total amount of methadone administered was able to predict deficits in WM, methadone treatment duration predicted psychomotor speed, and time since dosing predicted decision-making ability. Conclusions: To keep cognitive impairment at a minimum, methadone dose and treatment duration will have to be customized considering the history of opiate abuse so that impairment attributable to long-term opiate use may be differentiated from acute methadone dosing.