Suicide in people prescribed opioid-agonist therapy (OAT) in Scotland, 2011-2020: a national retrospective cohort study.

Background

Internationally, it is estimated that 700,000 people take their own life annually. Previous evidence shows that opioid dependence is associated with a substantial increased risk of suicide.

A large and consistent evidence base has shown that opioid-agonist therapy (OAT) reduces the risk of both overall mortality, and drug-related deaths (DRD) in particular with up to a 60% reduced risk. There is emerging evidence that OAT is protective against suicide with risk reduced by approximately 50% for those on OAT, compared to those off OAT. However, the evidence base on suicide risk and the preventative role of OAT to date is limited.

The main aim of this study was to examine the risk of Suicide among people prescribed OAT in Scotland. Our objectives were to determine if OAT is protective against suicide and whether suicide risk in people with opioid dependence followed trends in DRD or general population suicide rates in Scotland. 

Methods

We undertook a national retrospective cohort study of individuals in Scotland who received at least one prescription for OAT between 2010 and 2020. Records were linked to mortality data from National Records of Scotland, and other healthcare datasets (including sociodemographic and comorbidity) held by Public Health Scotland. The primary outcome measure was suicide, as defined by national statistics. We calculated standardised mortality ratios (SMR) using the age and sex specific suicide rates in Scotland for years 2011-2020. We then fitted multivariable competing-risk regression models (with all-cause mortality as the competing event) to determine whether OAT was protective against suicide and to estimate trends over time, adjusting for potential confounders. 

Results

Between 1 Jan 2011 and 31 Dec 2020, 46,453 individuals received at least one OAT prescription with over 304,000 person years (py) of follow-up. There were 575 deaths classed as suicide among the cohort and the overall suicide rate was 1.89 (95% CI 1.74-2.05) per 1,000 py. The age and sex SMR for suicide was 7.89 times (7.27-8.56) higher than in the general population. 

After adjustment, OAT was shown to be highly protective against suicide risk, where the risk of suicide was more than three times greater (adjusted HR: 3.07; 95% CI 2.60-3.62) off OAT compared to on OAT. Suicide risk decreased over time, falling from 2.57 (2.19-3.02) per 1,000 py in 2011-12, to 1.48 (1.21-1.82) in 2019-20.

Conclusion

People with opioid dependence in Scotland are at a substantially greater risk of suicide than the general population. However, during a period where drug-related death rates in Scotland rose to globally high levels, our study suggests that suicide rates in this population may have declined. There was strong evidence that risk of suicide is lower among those on OAT. Maintaining and enhancing investment in drug treatment and suicide prevention is essential to sustaining these trends and reducing inequalities experienced by people who use drugs in Scotland.