Delay discounting (DD) procedure has been used to probe the extent to which behaviour is insensitive to its long-term consequences. During the DD task, participants are offered a choice between a small reward, which is delivered immediately, and a larger reward, which can be obtained only after a delay. Several studies has been reported that drug addicts are insensitive to future outcomes in DD. Previous studies indicated that Methadone Maintenance Treatment (MMT) decreases risky behaviors such as illegal drug use, needle sharing and risky sexual behaviors. But, there is a serious question that could it change underlying cognitive processing of risky behavior or not?

In this study, we evaluated 266 opioid dependents (age: 31±9 years, education: 10±3 years) before MMT entry on DD. 78 patients (30%) has been completed at least three month MMT and re evaluated on DD. The Mazour model was fitted to data (V=A/(1+kD)) (K: delay discounting coefficient, D: delay) and least square parameter estimation was used to estimate delay discounting coefficient.

K was significantly reduced after 3 month successful MMT (0.12±.6 vs. 3.9±12.6) (P values=0.016). Successful patients in MMT had lower K in baseline but not significantly.

MMT could improve future time horizons in underlying cognitive processing of decision making. Based on this study, We could accept more favorably MMT as a real effective addiction therapy not just a substitution between street drugs and state drugs.