Background Intentional drug overdose (IDO) is the most common form of hospital-presenting self-harm and has been linked with marked increases in risk of dying by suicide and other causes. The type of drug taken in IDO is one of several factors that influence the likelihood of IDO repetition and fatality following overdose. Previous research examining the fatality of an overdose according to the drug types taken has attributed fatal toxicity to a number of psychotropic drugs. However, these findings have limited applicability as they focus on overdose acts involving single drugs, which represent a small minority of fatal IDOs. We aimed to describe the overdose characteristics of fatal and non-fatal IDO, and to establish which drug types are linked with greater risk of subsequent fatality.
Methods Data pertaining to 65,069 non-fatal IDO presentations from the National Self-Harm Registry, Ireland and 365 fatal IDOs from the National Drug-Related Deaths Index, for the period 1st Jan 2007 to 31st Dec 2014, were used to describe overdose characteristics of fatal and non-fatal IDOs, to calculate their incidence and to estimate case fatality risk ratios.
Results The risk of death following IDO was 1.7 times greater for males than females and fatal cases were on average nine years older than non-fatal cases, with each increasing year of age increasing the risk of a fatal outcome by 4.3%. Multiple drug IDOs were over three times more likely to be fatal, compared to single drug IDOs. Tricyclic antidepressants were associated with a 15-fold increased risk of death and opioids a 12-fold increased risk, relative to non-opioid analgesics (the reference category). Although the absolute 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 in IDO.
Conclusion Male gender, increasing age and multiple drug use were associated with fatal IDO outcome, and tricyclic antidepressants and opioids in particular were associated with a significantly increased risk of death following overdose. These findings inform the relative fatality risk of drugs that are commonly taken in intentional overdose, contributing to existing evidence-base in relation to safe and appropriate prescribing to patients who are at risk of self-harm. Together with the identification of the predictors of a fatal overdose outcome, these findings highlight areas for targeted intervention to prevent fatal overdose and also key areas for further research.
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