PRimary Care Opioid Use Disorders treatment (PROUD) trial protocol: a pragmatic, cluster-randomized implementation trial in primary care for opioid use disorder treatment - Campbell, Cynthia I.; Saxon, Andrew J.; Boudreau, Denise M.; Wartko, Paige D.; Bobb, Jennifer F.; Lee, Amy K.; Matthews, Abigail G.; McCormack, Jennifer; Liu, David S.; Addis, Megan; Altschuler, Andrea; Samet, Jeffrey H.; et al. (Addiction Science & Clinical Practice, 2021)