Abstract
The level of happiness is low among patients with chronic mental or physical disorders. However, happiness and its association to sociodemographic and clinical factors remain unknown among patients with opioid use disorder (OUD) and people who inject drugs (PWID). This prospective cohort study aimed to examine self-reported happiness levels in patients with OUD/PWID, changes over time, and its associations with sociodemographic factors, opioid agonist therapy (OAT), and substance use. From 2017 to 2023, 967 patients with OUD/PWID were examined at baseline and one-year follow-up assessments in eight OAT outpatient and municipality clinics in Norway. Happiness was assessed with an eleven-point Likert scale and presented as percentage (from 0% "completely unhappy" to 100% "completely happy"). A linear mixed model analysed associations between exposures and outcomes at baseline and over time. Participants were predominantly men (71%), with a mean age of 43 (SD: 11); 87% received OAT. Mean happiness was 45% of min-to-max (95% CI: 35;54) with an 11% improvement over time. High substance use (-24%, 95% CI: -32; -16) was associated with lower self-reported happiness at baseline, but self-reported happiness increased over time among those with more substance use. Living with someone was linked to higher happiness compared to living alone.