Buprenorphine is a treatment medication that decreases mortality risks among people with opioid use disorder (OUD). Despite its efficacy, buprenorphine is underused in the US. Insurance restrictions are commonly cited as barriers to buprenorphine prescribing. Using Medicaid, Medicare Advantage, and commercial insurance formulary files, we examined insurance-imposed utilization restrictions for buprenorphine for OUD for each year from 2017 to 2021 by insurance type. Almost all plans covered immediate-release buprenorphine in 2021, with a general trend of decreasing prior authorization requirements and quantity limits since 2017. In contrast, two payers had relatively low coverage of extended-release buprenorphine, with only 46 percent of commercial plans and only 19 percent of Medicare Advantage plans covering this formulation. Even though most Medicaid plans covered extended-release buprenorphine in 2021, 37 percent required prior authorization. Policy makers and researchers concerned with buprenorphine insurance barriers should shift their attention to extended-release buprenorphine. State lawmakers could help address these barriers by mandating that insurers include extended-release buprenorphine on their preferred drug lists.