Buprenorphine hasn't been as effective as hoped[1] for addiction treatment specifically for people who have taken fentanyl.
[1]: https://www.statnews.com/2022/11/16/fentanyl-isnt-just-causi...
[1]: https://www.statnews.com/2022/11/16/fentanyl-isnt-just-causi...
(I work for Boulder)