The optimal, or even minimum, duration of medication treatment for opioid use disorder (OUD) needed to improve long-term outcomes has not been established empirically. As a result, health plans set potentially restrictive treatment standards to guide benefits and payment. To address this gap, we used a National Quality Forum measure for OUD medication treatment duration (180 days) to examine the impact of longer treatment on health care outcomes within a key population of Medicaid enrollees. Compared to buprenorphine discontinuation around the National Quality Forum benchmark (six to nine months), longer treatment (at least fifteen months) was associated with relative reductions in the risk of having all-cause inpatient (-52percent) and emergency department (-26percent) use, opioid-related hospital use (-128percent), overdose events (-173percent), and opioid prescriptions (-120percent) and in the rate of prescription opioid use (-124percent). We argue that these clinical benefits provide a rationale for policies that increase access to longer-term buprenorphine treatment, including lengthening the standards for minimum treatment duration.