AIMS To measure all-cause mortality risk after an ambulance-attended non-fatal opioid overdose and associations with number of days following attendance, and individual and clinical characteristics.

DESIGN A prospective observational study.

SETTING Oslo, Norway.

PARTICIPANTS Patients treated with naloxone for opioid overdose by Oslo Emergency Services between 1 June 2014 and 31 December 2018.

MEASUREMENTS Medical records were linked to the national Cause of Death Registry (1 June 2014-31 December 2019). Crude mortality rates (CMR) and incidence risk ratios (IRR) with 95% confidence intervals (CI) were estimated for the time periods (0-7 days, 8-31 days, 32-91 days, 92-183 days, >183 days) using multivariate Poisson regression analysis. IRR were estimated for sex, age, Glasgow Coma Scale (GCS), respiration rate, place of attendance and non-transportation following treatment. Robust variance estimates applied due to multiple risk periods. Standardized Mortality Rates (SMR) were estimated.

FINDINGS Overall, 890 patients treated for 1764 overdoses contributed to a total time at risk of 3142 person-years (PY). Median number of attendances was 1 (range 1-27). The majority were male (75.5%) and the mean age was 37.7 years. In total, 112 (12.6%) died; 5.2% within 183 days and 2.2% between 184 and 365 days. Acute poisoning was the most common single cause of death (52.7%). The CMR was 3.6 (95% CI = 3.0-4.2) per 100-PY. The women had a SMR of 32 (95% CI = 15.8-57.9) and the men 24.9 (95% CI = 17.7-34.2). The CMR (22.2, 95% CI = 10.6-46.8) was particularly high in the first 7 days, and significantly higher than in the following periods. However, this finding was only valid for those with severe overdose symptoms (GCS score = 3/15 and/or respiratory rate ≤6/min). Except for increasing age, no other indicators were associated with the mortality risk.

CONCLUSION Patients treated by Oslo Emergency Services between June 2014 and December 2018 for a non-fatal opioid overdose with severe overdose symptoms at attendance had an overall high mortality risk compared with the general population, but particularly during the first 7 days after attendance.