Abstract Importance Cannabis sativa, the most widely used illicit substance in Canada, has a unique ability to facilitate relaxation and relieve anxiety while reducing pain. However, no study to date has examined quality of life (QOL) and psychosocial issues in relation to the use of this drug among patients with newly diagnosed head and neck cancer (HNC). Objective To examine the differences in QOL and psychosocial outcomes between marijuana users and nonusers with newly diagnosed HNC. Design, Setting, and Participants This prospective cohort study was conducted at a tertiary care cancer center. Patients were enrolled consecutively and prospectively at the time of HNC diagnosis from January 1,...