Opioid overdose deaths and the expansion of opioid agonist treatment: a population-based prospective cohort study.

BACKGROUND AND AIM

Effective policies to reduce drug-related overdoses remain a public health priority. We aimed to estimate the causal effects of a national opioid agonist treatment (OAT) program on population level drug fatalities.

DESIGN

Population-based prospective cohort study exploiting supply driven variation in treatment uptake across cohort-age groups generated by the introduction and scale-up of a national OAT program. A Poisson difference-in-differences model with an intention-to-treat design was used to assess how treatment uptake altered the age profile of risks and infer treatment effects on drug fatalities.

SETTING

Norway, from 1996 through 2016.

CASES

The data include a total of 5634 drug-related overdose deaths and cover the introduction of the Norwegian OAT program in 1998 and its initial growth period, reaching 12 286 ever-treated recipients by 2016.

MEASUREMENTS

Fatal opioid-related overdoses were defined as deaths with a primary cause assigned an International Classification of Diseases 10th Revision (ICD-10) code F11, or X42, X44, X62 or X64 in combination with T40.0-T40.4. Other non-opioid related fatal overdoses were defined by a primary cause registered as F12, F14, F15, F16 or F19, or X42, X44, X62 or 64 in combination with T40.5-T40.9.

FINDINGS

An additional 887 deaths (95% credibility interval [CI] = 265-1563) would have been expected in the absence of OAT, which implies one death avoided per 111 (95% CI = 61-342) treatment-exposed person-years. At scale, the program reduced annual overdose mortality by 27% in 2016 (95% CI = 10%-41%) relative to a no-OAT counterfactual, corresponding to 99 fewer expected fatal overdoses (95% CI = 28-180) in 2016. Analysing fatal opioid-related and other drug overdoses separately found similar numbers for avoided opioid-related fatalities (921, with 95% CI = 373-1526) and no treatment effects on non-opioid related fatalities (-38, with 95% CI = -193-154).

CONCLUSION

The introduction and rapid scale-up of a national opioid agonist treatment program in Norway was associated with substantial and plausibly causal reductions in drug fatalities.