Intentional drug overdose (IDO) is the most common method of hospital-presenting, non-fatal self-harm¹ and has been linked with an increase in premature mortality risk due to suicides, accidents, and other causes.² Importantly, the risk of mortality due to suicide is increased among persons who have engaged in IDO and in 2018 intentional overdoses resulted in 7,792 presentations to Irish hospitals.³ Multiple drugs are present in between 26% and 41% of non-fatal IDOs, increasing to 64% in fatal overdoses.^4,5,6 Nevertheless, despite the involvement of multiple drugs in IDO, the case fatality of drugs taken in multiple drug overdoses remains under-researched and little is known about how case fatality risk varies according to the type of drug(s) taken.

A recent Irish study aimed to examine the incidence of IDO in Ireland, to identify the predictors of fatal IDO, and to establish which drugs are linked with greater risk of a fatal outcome.⁷ In this research, published in the International Journal of Drug Policy, data from the National Self-Harm Registry and the National Drug-Related Deaths Index, 2007–2014, were used to calculate incidence, to examine overdose characteristics, and to estimate case fatality risk ratios.

There were 63,831 non-fatal and 364 fatal IDOs during this period (incidence: 148.8 and 1.01 per 100,000, respectively). Compared with non-fatal IDOs, fatal cases were more likely to be male (55.2% vs 42%), were older in age (median 44 vs 35 years), and more frequently involved multiple drugs (78.3% vs 48.5%). The study found that tricyclic antidepressants were associated with a 15-fold increased risk of death, while opioids were associated with a 12-fold increased risk, relative to the reference category (non-opioid analgesics). While the risk of fatal outcome was higher for males than females, the elevation in risk was greater in females when tricyclic antidepressants or opioids were taken.

As tricyclic antidepressants and opioids were found to be associated with a significantly increased risk of death, the authors concluded that these results add to the current evidence regarding the risk and potential adverse outcomes associated with these drugs. Findings may help inform safe and appropriate prescribing, where clinicians consider the fatality risk of drugs when determining treatment for patients at risk of self-harm, or who have previously harmed themselves.

1 Perry IJ, Corcoran P, Fitzgerald AP, Keeley HS, Reulbach U, et al. (2012) The incidence and repetition of hospital-treated deliberate self harm: findings from the world’s first national registry. PloS One 7(2): e31663.

2 Finkelstein Y, Macdonald EM, Hollands S, Hutson JR, Sivilotti MLA, Mamdani MM, et al. (2015) Long-term outcomes following self-poisoning in adolescents: a population-based cohort study. Lancet Psychiatry, 2(6): 532–539.

3 Griffin E, McTernan N, Wrigley C, Nicholson S, Arensman E, Williamson E, et al. (2019) National Self-Harm Registry Ireland: annual report 2018. Cork: National Suicide Research Foundation. https://www.drugsandalcohol.ie/31193/

4 Daly C, Griffin E, Ashcroft DM, Webb RT, Perry IJ and Arensman E (2018) Frequently used drug types and alcohol involvement in intentional drug overdoses in Ireland: a national registry study. Eur J Public Health, 28(4): 681–686. https://www.drugsandalcohol.ie/28709/

5 Finkelstein Y, Macdonald EM, Hollands S, Sivilotti MLA, Hutson JR, Mamdani MM, et al. (2015) Risk of suicide following deliberate self-poisoning. JAMA Psychiatry, 72(6): 570–575.

6 Health Research Board (HRB)(2015) National Drug-Related Deaths Index 2004 to 2015 data. Dublin: Health Research Board. https://www.drugsandalcohol.ie/28086/

7 Daly C, Griffin E, Corcoran P, Webb RT, Ashcroft DM, Perry IJ and Arensman E (2020) A national case fatality study of drugs taken in intentional overdose. Int J Drug Policy, 76: 102609.