目的：鴉片類依賴是慢性長期易復發的疾病，美沙冬替代治療從2005年開始引進台灣，然而，病人在美沙冬替代治療中，有高退出率引起關注。此研究目的在討論台灣美沙冬替代治療留置率其相關因子。方法：此研究為回顧性世代研究，納入中部四家醫院參與美沙冬替代治療的病人，從2007年1月到2009年5月，共有1944位納入此研究。依照其留置在美沙冬替代治療的時間分為1-30、31-90、91-180、181-360及超過360天。結果：病人的美沙冬替代治療留置率，隨著時間逐漸減低，只有290位(14.99%)病人在美沙冬替代治療超過360天，留置時間越長的組別美沙冬劑量越高。年紀大的病人較年輕的病人，待在美沙冬替代療法，有顯著較久(p ＜ 0.05)。使用海洛因時間較久的病人，待在治療也有顯著較久(p＜ 0.05)。病人在離開美沙冬替代治療時，美沙冬劑量不穩定變動較大。結論：高劑量美沙冬及年紀較長病人在美沙冬替代治療時間會比較長，另外美沙冬劑量的大變動可能與退出治療相關。

Objective: Opioid dependence is a chronic and relapsing disorder. In Taiwan, the methadone maintenance treatment (MMT) has been introduced since 2005. But high dropout rate from the MMT patients has been high. In this study, we intended to explore the related factors for patients’ retention duration in the MMT program in Taiwan. Methods: This is a retrospective cohort study. We reviewed the charts of subjects enrolled in the MMT program at four sites in central Taiwan. Totally, 1,944 heroin users in the MMT program were enrolled consecutively from January 1, 2007 to May 31, 2009. Five groups of the MMT duration were divided into 1-30, 31-90, 91-180, 181-360, and more than 360 days. Result: The retention rate of the MMT was gradually decreased with the time. Only 290 (14.99%) subjects stayed in the MMT for more than 360 days. Higher dosage of methadone was found in subgroups of longer retention of MMT. Elderly patients who stayed in the MMT, were found to be staying longer than younger ones (p ＜ 0.05). Patients staying longer in the MMT had longer duration of heroin use (p ＜ 0.05). Unstable dosage of methadone was found to be more in those patients before their withdrawal from the MMT program. Conclusion: Our study gained important information that higher dosage and older age would be a favorable factor for longer retention duration in the MMT in Taiwan. Furthermore, dramatic changes in dosage could lead to patients’ withdrawal from the MMT program.