Moallef S, DeBeck K, Fairbairn N, Cui Z, Brar R, Wilson D, Johnson C, Milloy MJ, Hayashi K Inability to contact opioid agonist therapy prescribers during the COVID-19 pandemic in a Canadian setting: a cross-sectional analysis among people on opioid agonist therapy Addict Sci Clin Pract PubMed