Integrative exploration of bio-psycho-social determinants of DSM-5 severity levels of opioid use disorder: the BEBOP cohort study protocol. - Lalanne L; Lutz PE; Caparros-Roissard A; Ruppert E; Waeckerle G; Scherer C; Oster F; Brand C; Henck S; Soavelo H; Ramousset C; Lebreton M; et al. (BMJ open, 2025)