The aim of this study is to describe cases of self-harm with substance use from April 2011 to September 2019, based on eCHIRPP data. The mean age of patients in this study was relatively young but consistent with other eCHIRPP studies, given that the majority of participating hospitals are paediatric [24]. As previously reported, both nationally and internationally, our study found that adolescent females accounted for the majority of cases presenting to the ED with self-harm with substance use [5, 8, 10, 12, 25]. Similar to findings presented by Canner et al., (2018) [10] our study found that while the overall age group distribution for males and females were similar, the percentage for females was much higher. Possible reasons for this are that women attempt suicide more frequently than men, peaking in mid-adolescents, while men are more likely to die by suicide due to the use of more violent methods [10, 26]. Non-substance-related suicides may be more likely to bypass the ED and not be captured in eCHIRPP. Another potential reason is that females who misuse substances are more likely to be injured, and present to hospital, as compared to males [27]. Fatalities among our sample were low; however, it is worth noting that the majority of cases, for both sexes, required admission to hospital indicating the severity of the self-harming behaviour. Overdose, whether intentional or unintentional, can lead to irreversible organ damage such as kidney and liver failure [28, 29] with poorer outcomes typically reported in older patients [30].

As demonstrated in previous studies [31], medications (both prescription and non-prescription) were used most frequently by both sexes. A study examining prescription medication availability found that patients who engaged in deliberate self-poisoning had a greater prescribed medication load than the general population [32]. Cases involving prescription medications sometimes included opioids; however, the eCHIRPP database is not able to report whether the ingested opioid was prescribed to the patient or prescribed to someone else in the household (e.g., belonging to a parent). Given that opioid-related deaths and hospitalizations have been increasing in Canada [33], the safe storage and disposal of medications, even in households with older children, may be a necessary prevention strategy [8]. Other strategies include restricting packet size of over-the-counter medications, restricting the sale of medications to pharmacies (i.e., not other retail outlets), and restricting sales to persons 18 years and over [34, 35]. Following medications, the use of multiple types of different substances were used most frequently, with alcohol dominating as a co-occurring substance in this category. History of alcohol use with other mechanisms of self-harm has been noted in other studies [34]. Further, alcohol use disorder has been associated with an increased risk of suicide ideation, suicide attempt and death by suicide [36]. Men were more likely than women to use illicit drugs in combination with other types of substances. Overall, cannabis was more likely to be used with other substances than in isolation. A previous study found that, medications and illicit drug use were significantly associated with hospitalizations while cannabis was not [37].

The time trend analysis demonstrates a significant trend among both sexes and all ages, particularly since about 2016. Part of this increase may be surveillance artifact due to improved capture and/or increased reporting (see limitations section). A relatively recent increase in awareness of mental health issues, and a reduction of the stigma associated with mental health, through national initiatives and social media campaigns around 2011 [38] may also account for part of this increase. It is also worth noting that the time-period of this study is pre-COVID-19 pandemic period. There is some evidence that substance use and self-harm have increased during the pandemic [39], and the results of this study represent a baseline for comparison in future studies (which are currently underway).

The proportion of observations, treatments and admissions were significantly higher among patients presenting to the ED with substance-related self-harm injuries and poisonings compared to the referent population, as noted in our PIR analysis. Two important considerations may help explain our results. First, the magnitude of these findings are reflective of the large proportional difference of the presence of substances among self-harm cases compared to those categorized as unintentional. Specifically, while the majority (58.5%) of all self-harm cases documented the presence of one or more substances – a finding consistent with previous studies [10, 40, 41] – the presence of one or more substances among all cases categorized as unintentional injuries and poisonings was reported in only 2.8% of cases (data not shown). Such a large discrepancy can contribute in magnifying the PIRs, even while adjusting for age and sex.

The second consideration takes into account the nature of these cases, whereby the deliberate self-harm by patients may in some instances warrant a greater need for medical attention compared to those who unintentionally or recreationally consumed substances. For instance, in our study, prescribed and/or over-the-counter accounted for the majority (55%) of all substance-related self-harm cases. This finding may be indicative of the clinical severity of such cases, as evidenced by a number of studies highlighting the acute health complications of prescription and over-the-counter medication overdoses [42–44] and thereby offering an explanation of the noted large PIRs in all levels of care, especially those regarding hospital admission, a level reflecting the need for further treatment and/or observation.

Additionally, though the quantity and dosage of ingested substances are not regularly reported in eCHIRPP records, a recent national study conducted in Ireland may also help provide insight on the gravity of consumption patterns of self-harming patients presenting in health care settings. Results of Cully et al.’s study [45] showed that, when specified, the majority of self-harming patients presenting to the ED consumed in the range of 20 or more tablets of prescription or over the counter medications or illicit substances. Though dose and substance dependent, such excess may have serious health implications requiring important medical intervention. If similar consumption patterns are found among the Canadian population, it may offer insight of the noted PIRs observed in our study, all pointing to higher proportions of observations, treatments and admissions among patients presenting to the ED with substance-related self-harm injuries and poisonings compared to the referent population. A Canadian study comparing detailed consumption patterns among substance-related self-harm cases and substance-related unintentional harm cases may help shed light in this area.

Text fields revealed additional notable findings. A high percentage of cases in each age group reported that the self-harming event was either an attempted suicide or included suicidal ideation. As reported in other studies, ED text fields involving substance use often included descriptions of depression, or feelings of sadness or being overwhelmed [24, 37]. Exposure to difficult life-events can lead to self-harm [4]. Stressful interpersonal events, such as conflicts with family members, conflict or a breakup with a partner, assault or bullying were reported as influencing factors leading up to the self-harming event. The capacity of people to cope with stressors can vary by age, sex and their ability to access supports [26]. Further, due to their developmental stage, adolescents may be more susceptible to reacting to negative social interactions and cues than adults [4]. Consistent with other studies [10, 25, 46], some cases identified the presence of a pre-existing mental health condition such as depressive or anxiety disorders, especially among youth. Although not a significant number of cases reported past or repeated self-harm in our study, it has been identified as a risk factor for eventual suicide [2, 47]. A systematic review found that the incidence of fatal repeat self-harm was 1.6% of patients within 1 year, increasing to 3.9% by 5 years and 4.2% at 10 years [3].

While our study did not capture a large sample of older adults, other studies have reported a high incidence rate of suicide related ED visits made by older adults involving the use of drugs, alcohol or both [48]. Later-life mental health and substance use disorders are risk factors for self-harm in older adults presenting to the ED, and contribute to outcomes that require more intensive and long-term health care services for this population [49]. Although less information exists on self-harm and middle aged adults, data from the US indicates that suicides among 35-64 year olds increased between 1999 and 2010 and self-poisonings were the second most common method used [50].

Finally, previous ED studies have demonstrated that cutting carries a greater risk of repetition and eventual suicide than poisoning, among adolescents [4]. Of those admitted to hospital, our study found cutting (and less often stabbing) accompanied substance use as an additional self-harming mechanism in cases among all age groups, and was reported in cases with reported suicide attempt and suicidal ideation. This may be considered a notable finding given that debate exists as to whether self-harming behaviours such as cutting should be exclusively categorized as a non-suicidal self-inflicted injury [51].