Objectives: Since 2009, the Taiwanese government has subsidized treatment for non-AIDS-related drug addiction. The aim of this retrospective cohort study was to investigate the effect on National Health Insurance (NHI) resources of treatment for people with addiction who enrolled in a methadone substitution treatment program. Methods: Data from 2009 to 2014 of people with drug addiction who were treated with methadone were collected as samples. Analytical tools such as the Inverse Probability of Treatment Weighting (IPTW), which is based on propensity score and weighted multiple regression, were used to further compare the use of NHI resources by the stable-treatment and interrupted-treatment groups. Individual characteristics of sex, age, and income level were controlled for in addition to the level, ownership, and Bureau of NHI branch of the medical institution. Results: According to the weighted multiple regression analysis results of the NHI point values of the outpatient and emergency departments, the NHI point values of the stable-treatment group increased by 9% relative to the interrupted-treatment group (p = 0.0023). The results of a Poisson regression on the NHI utilization frequency of outpatient and emergency department visits indicated that with the same control variables, the average NHI utilization frequency of the stable-treatment group increased by 14% relative to the interrupted-treatment group (p ＜ 0.001). Conclusions: Among people with addiction who enrolled in the methadone substitution treatment program, those in the stable-treatment group had not only higher logarithmic NHI point values but also higher NHI utilization frequency in their outpatient and emergency department visits compared with the interrupted-treatment group. Although no statistical significance was observed, further research should investigate why, after IPTW, the average annual inpatient point values for the interrupted-treatment group were higher than those for their stable-treatment counterparts.