NDARC Technical Report No. 67 (1999)
EXECUTIVE SUMMARY
Aims: This report compares trends in the rates of deaths attributed to opioid overdose and suicide among young Australia adults over the period 1964 to 1997.
Method: Data on the age at death and gender for deaths attributed to suicide and opioid overdose were obtained from the Australian Bureau of Statistics for the years 1964 to 1997. Suicide and opioid overdose mortality rates for each year were estimated for males and females aged 15-24 years, 25-34 years, and 35-44 years. Proportional mortality analyses were used to examine differences between each of eight five-year birth cohorts (1940-44, 1945-49, 1950-54, 1955-59, 1960-64, 1965-69, 1970-74, 1975-79) in the proportion of all deaths attributable to opioid overdose and suicide. The cumulative proportional mortality was also estimated for each of the birth cohorts.
Results:
1) Opioid overdose deaths
The number of deaths attributed to opioid overdose among Australian adults aged 15-44 years increased from 6 in 1964 to 600 in 1997. The proportion of all deaths attributed to opioid overdose in this age group increased from 0.1% in 1964 to 7.3% in 1997, while the mortality rate per million population increased from 1.3 in 1964 to 71.5 in 1997. There were marked differences between birth cohorts in the proportion of deaths that were attributed to opioid overdose. Persons born between 1944-49 had a consistently low proportion of deaths attributed to opioid overdose throughout the period 1964-1997, while successive birth cohorts showed progressively higher proportions of deaths due to opioid overdose. The onset of the increase in overdose mortality began at progressively younger ages in each successive cohort.
2) Suicide deaths
The number of suicide deaths among Australian adults aged 15 to 44 years increased from 720 in 1964 to 1718 in 1997. The rate per million in this age group increased from 152.3 in 1964 to 204.6 in 1997, while the proportion of all deaths attributed to suicide increased from 9.7% to 20.8%.
3) Opioid overdose compared with suicide
The pattern of age-related mortality trends differed between these two causes: suicides occurred among younger adults than opioid overdose deaths, and the average age at death has been decreasing for suicide, while it increased for opioid overdose, with both converging around 30 years. The cumulative proportion of all deaths attributed to suicide increased over the eight birth cohorts in a similar way to opioid overdose deaths, but with one difference, namely, the increase in the proportion of deaths attributable to suicide peaked at an earlier age than that for overdose in each birth cohort.
Discussion: There has been a steep increase in the number and rate of opioid overdose deaths among young Australian adults between 1964 and 1997, an increase that was much steeper than the increase in suicide deaths. Opioid overdose deaths now account for 1 in 11 deaths, while suicide deaths account for 1 in 5 deaths. Together, these two causes account for almost 30% of deaths among Australian adults aged 15-44 years.
Explanations of trends in opioid overdose: The increase in the rate of fatal opioid overdose in Australia between 1964 and 1997 is unlikely to be an artefact of changes in the way in which deaths among young adults have been classified. Any such change in diagnostic practice would have to be very marked to explain the fifty six-fold increase in mortality rate from these causes between 1964 and 1997. These changes would also need to have varied markedly with age and sex to explain the observed trends.
The increase in overdose mortality, and the striking birth cohort differences in mortality, are most plausibly explained by an increase in the prevalence of heroin use among subsequent birth cohorts between 1964 and 1997. This hypothesis is supported by historical data on trends in illicit heroin use over the period.
An increase in average heroin purity between 1992 and 1995 has probably contributed to the recent increase in opioid overdose mortality. The higher the blood morphine level, all else being equal, the easier it will be for a heroin user to overdose. Nonetheless, purity is unlikely to be the sole explanation of the increase because mortality increased steadily throughout the study period, rather than being confined to the last three years. If increased heroin purity was the sole explanation of the increase one would expect more deaths among new recruits to heroin use who would have the lowest tolerance for opioid drugs and be the least experienced in judging the purity of street drugs. But the typical overdose fatality in 1997 was a 30 year old male with a 12 year history of regular heroin use.
A number of changes in patterns of drug use may have contributed to the increased rate of opiate overdose deaths between 1979 and 1995. These include: more risky patterns of heroin use, such as injecting alone, or in the street; and an increase in the use of CNS depressant drugs among opioid users, especially by injection. Some of these trends have been observed in New South Wales but it is uncertain how widespread they have become. It may also be that more risky drug use patterns are adopted as opioid users age.
A steady expansion in methadone maintenance treatment over the study period is unlikely to be the explanation of the increase in overdose deaths. This is due to the fact that 80% of opioid overdose deaths in New South Wales between 1990 and 1995 were due to heroin, and methadone maintenance also reduces clients' risk of overdose mortality.
Implications: Public concern about suicide deaths has prompted national efforts to prevent these deaths among young adults. There has not been a similar concern about nor effort to prevent opioid overdose deaths. There is an urgent need for: education of drug users and their peers about safer drug use practices and effective responses to overdose; increased treatment options for heroin users; and interventions to reduce initiation of heroin use by young persons at high risk of doing so.