Effect of cannabis use in people with chronic non-cancer pain prescribed opioids: findings from a 4-year prospective cohort study oleh Gabrielle Campbell, PhD, Wayne D Hall, PhD, Amy Peacock, PhD, Nicholas Lintzeris, MD, Raimondo Bruno, PhD, Briony Larance, PhD, Suzanne Nielsen, PhD, Milton Cohen, MD, Gary Chan, PhD, Richard P Mattick, PhD, Fiona Blyth, PhD, Marian Shanahan, PhD, Timothy Dobbins, PhD, Michael Farrell, MD, Louisa Degenhardt, PhD