In this cross-sectional study of all-payer pharmaceutical data, findings showed that while mean daily out-of-pocket costs for buprenorphine decreased between 2015 and 2020, costs continued to vary by payer and remain high for some in 2020. Public health and insurer strategies aimed at reducing higher patient out-of-pocket costs may address financial barriers and improve buprenorphine treatment retention. Future research might continue to examine how cost-sharing may impact MOUD treatment initiation and retention under different payers.