NDARC Technical Report No. 39 (1996)
Blood toxicology results for all accidental heroin 'overdose' deaths that occurred in the south western Sydney region during 1995 (N=39) were compared to those of a sample of 100 current south western Sydney heroin users who had injected within the preceding 24 hours. Overall, fatal overdose cases had a higher median concentration of morphine than the needle exchange attendees (0.35mg/L v 0.09 mg/L). However, there was substantial overlap between blood morphine concentrations of the two groups, ranging from 0.08 mg/L to 1.45 mg/L. The overlap covered 90% of heroin-related deaths. A third of current users had morphine concentrations more than twice the toxic morphine blood level employed by the analytical laboratories, and 7% had morphine levels higher than the median recorded for fatal cases. Only 4 of the 39 heroin-related fatalities had blood morphine concentrations exceeding the highest recording for the current user group.
There was a marked contrast in the prevalence of alcohol detected in the groups. Alcohol was detected in 51% of fatal cases (median=0.10g/100ml) compared to only one current heroin user (1%). There was a significant negative correlation among fatal cases between blood morphine and blood alcohol concentrations (r = -0.41). The overlap between the morphine distributions of current heroin users and fatalities involving alcohol was substantially greater than between current users and alcohol negative cases.
There was no significant difference between the proportions of fatalities and current heroin users in which benzodiazepines were detected in the blood. Both alcohol and benzodiazepines were detected in 10% of fatal cases compared to 1% of current heroin users. Methadone was detected in one (2%) fatal case, and in 27% of current heroin users.
These data further call into question the assumed mechanisms underlying heroin fatalities. It is clear that a conclusion of heroin overdose cannot be based on blood morphine concentrations alone.
The study also supports previous work implicating the role of alcohol in what are reported as heroin overdoses. Alcohol was detected in over a half of heroin fatalities, compared to only one current heroin user. These data, taken in conjunction with previous studies, indicate that strategies to reduce the morbidity and mortality of heroin overdose should focus on the role of alcohol.