Background: Drug-related death (DRD) rate in Scotland, UK, has increased rapidly to one of the highest in the world. Our aim was to examine the extent to which opioid-agonist therapy (OAT) in Scotland is protective against drug-related mortality and how this effect has varied over time.

Methods: We included individuals in Scotland with opioid use disorder who received at least one OAT prescription between Jan 1, 2011, and Dec 31, 2020. We calculated drug-related mortality rates and used Quasi-Poisson regression models to estimate trends over time and by OAT exposure, adjusting for potential confounding.

Findings: In a cohort of 46 453 individuals prescribed OAT with a total of 304 000 person-years of follow-up, DRD rates more than trebled from 6·36 per 1000 person-years in 2011–12 to 21·45 in 2019–20. DRD rates were almost three and a half times higher for those off OAT compared with those on OAT after adjustment for confounders. However, confounder adjusted DRD risk increased over time for both people off and on OAT.

Interpretation: Drug-related mortality rates among people with opioid use disorders in Scotland increased between 2011 and 2020. OAT remains protective but is insufficient on its own to slow the increase in DRD risk for people who are opioid dependent in Scotland.