Profile differences between overdose and non-overdose suicide attempts in a multi-ethnic Asian society

Study design

A total of 485 assessment records of admitted adult suicide attempters aged 21 years old and above from January 2009 to December 2012 were extracted from a general hospital (National University Hospital, Singapore) database. Data sources included the suicide risk assessment forms, psychiatric reports, in-patient records and electronic notes. The assessment was done by the psychiatrist and this was part of the protocol of standard operating procedures for patients admitted following a suicide attempt. The interview was based on a semi-structured checklist approach. A formal diagnosis was made by the psychiatrist based on the Diagnostic and Statistical Manual of Mental Disorders Fourth Edition (Text Revision) (DSM-IV-TR) criteria.

The suicide risk assessment form that was used in the study contained stressors that comprised of work-related issues, family-related issues, relationship problems, financial difficulties and medical illnesses; risk factors that included history of psychiatric illnesses, family history of psychiatric illnesses, staying alone, alcohol or substance misuse, ongoing interpersonal problems, lack of confidantes, serious physical illnesses, poor coping skills, severe financial problems and unemployment; and protective factors that consisted of faith in a religion, resolution of precipitants, receiving support from dependents, expression of regret, positive plan for the future, willingness to seek help and good emotional support. All suicide attempters were also asked to rate their impression of lethality of their suicide method as part of the suicide risk assessment, which ranged from ‘not lethal’, ‘moderately lethal’ to ‘very lethal’.

This assessment form was created by a team of psychiatrists in the department based on known common risk factors of suicide. The initial and main aim of the checklist form was to serve as a clinical tool for the assessing psychiatrist to avoid missing out on the common possible stressors and risk/protective factors. To standardize the assessment, all the psychiatrists were briefed and trained on asking the questions in the form so that they could reach a common consensus on the terms and what they meant prior to using the form.

Attempters were classified into either the OD group if there were indications of consumption of pharmacological or chemical substances in the attempt or the NOD group for all other forms of deliberate self-harm, including lacerations, stabbing, jumping from height and hanging. Written informed consent was obtained from all the participants in the study. The study was approved by the Domain Specific Review Board (DSRB) (DSRB Reference: 2013/00800).

Statistical analysis

The Statistical Packages for Social Sciences (SPSS) Version 21.0 software was used to perform statistical analysis. The Chi-square test was conducted to examine differences in characteristics and suicidal behaviours between and within the OD and NOD groups. The Mann-Whitney U test was employed to determine differences in hospital admission data between the OD and NOD attempters. The assumption of similarly shaped distributions was ascertained by visual inspection. Logistic Regression was used to test for differences between the self-perceived lethality of the suicide methods employed between OD and NOD groups.

Socio-demographic and characteristics of attempts

Risk and protective factors

Characteristics of attempts in OD group

Self-perceived lethality of the suicide methods

Only 46.7 % of female OD suicide attempters perceived their attempts as lethal as compared to 58.6 % of males perceiving their attempts as lethal (OR = 0.62, p = 0.02). Chinese OD suicide attempters had higher perceived lethality of their suicide methods (OR = 0.64, p = 0.03) as compared to all other ethnicities. All other demographic factors did not have significant impact on their perceived lethality (Table 1).

Frequency and distribution of suicide attempts across Singapore

The lowest number of suicide attempts occurred on Fridays (46 attempts, 9.48 %) and Saturdays (47 attempts, 9.69 %) for both OD and NOD groups, whilst the highest occurred during mid-week on Wednesdays for the OD group (75 attempts, 15.46 %) and on Thursdays for the NOD group (13 attempts, 2.68 %). The lowest number of attempts was in the month of January for both OD and NOD groups (16 attempts, 3.30 %), whilst the highest occurred in the month of May for the OD group (50 attempts, 10.31 %) and in April for the NOD group (12 attempts, 2.47 %).

An exploratory analysis of geographical distribution of attempts showed that areas in Singapore with more than 20 suicide attempts had a high density of high rise residential buildings. Presence of industrial estates that is typically more isolated had little impact on the number of suicide attempts.

Socio-demographic factors

Our results suggested that ethnicity may influence the choice of suicide method, with Indians tending to choose OD over NOD methods. This finding is also in concordance with several studies of completed suicides carried out in Malaysia [17–19], a neighbouring country of Singapore which also has these three ethnicities (Malay, Chinese, Indian) in their population make-up. Due to lack of data from the sources, it was a challenge to identify the motivating factors for choosing OD over NOD methods. However, the near significant gender difference in suicide methods observed in our results, mirrored evidence in the literature that women tend to use less violent suicide methods like poisoning [20, 21] as compared to men who tend to use NOD methods such as hanging [22].

Precipitants and risk factors

Majority of the attempts in both groups were unplanned, precipitated by relationship, family, or work problems and some attempters were observed to have acute stress reaction, depressive disorder or adjustment disorder. This is supported by a study by Chia et al. [23] that identified relationships and job- related problems as social risk factors of suicide in Singapore. Non-Chinese OD suicide attempters and females were also more likely to perceive their suicide as less lethal. Individuals who make impulsive attempts tend to carry out their plans without pre-meditation and expect their method to be less lethal than the actual lethality [24]. Therefore, it is possible that some of the suicide attempts might have been carried out on impulse due to inability to cope with life stressors. Further research will be required to delve deeper into the mechanisms behind impulsive NOD and OD suicide attempts.

Attempters who lived alone or had a lack of confidantes had a higher risk of attempting suicide with OD methods than the NOD group. There were also fewer protective factors in the OD group, as attempters did not have good emotional support and were less willing to seek help. Social support has been found to be associated with decreased likelihood of a lifetime suicide attempt [25], suggesting that providing timely social support to attempters in times of need might help to reduce the number of OD attempts.

Characteristics of OD attempts

The most common drugs consumed in the OD group (analgesics, hypnotic agents, domestic products, flu medications and antidepressants) can be easily purchased over the counter or obtained through prescription by a general practitioner for sleep and mood disorders. Evidently, the ease of obtaining a substance for OD is of major importance in suicide attempts. Means restriction is an important population strategy for suicide prevention [26]. Thus, if high enough barriers to lethal drugs are imposed, it may lead to a reduction in likelihood of overdosing on a particular substance [27] and reconsideration of the impulse to attempt suicide [28]. Further research is recommended to ascertain the need for more rational prescribing and stricter control over quantities of common medications that can be bought over the counter.

Time and geographical patterns of suicide attempts

Different periods of a week or year may lead to variation in the number of suicide attempts due to differing environmental conditions and stressors [29]. Fridays leading up to weekends correspond to times of less stress and therefore leading to a fall in number of attempts in our study. Number of suicide attempts increased again just before the start of the week on Sundays. There is a build-up of stress levels on weekdays from Mondays to Thursdays, leading to increased suicide attempts. This is also consistent with the trends for completed suicides [30, 31]. Since the months of March, April and May are the hottest months in Singapore [32], higher ambient temperatures leading to increased stress in attempters may correspondingly explain the highest number of suicides in these months. Similar reports have been made for completed suicides [33, 34], and this is postulated to have underlying sociological, biological, or psychological mechanisms which are still under intensive research [35, 36]. The lowest number of suicide attempts in January and February can be explained by the fact that they are the first few months of the year with major national holidays which could be associated with the positive outlook that things will change for the better. This is in accordance with major holidays being preceded by lower number of suicide attempts [37, 38].

Additionally, our data on geographical distribution indicated that attempts tended to occur at home and in high density residential areas. This provides insight on how suicide prevention or intervention strategies can be formulated to reach out to attempters or people contemplating suicide in their homes.

Strengths and limitations of study

While our study included a large sample size of patients, it is not without limitations. Firstly, the sample was obtained from only one general hospital and it only included those with attempted but not those who completed suicide. Our sample consisted of mainly younger adults and not the elderly, which reduces generalizability of the findings to other age groups. Furthermore, the NOD group had a small sample size and thus might not have been representative of the NOD suicide attempters of Singapore. Within this group, there was heterogeneity in terms of the method of suicide, which varied from laceration to jumping from height and hanging, and this carried different degrees of lethality. The measures indicated in the suicide risk assessment form were based on clinician judgement and there was no inter-rater reliability for assesment. The cross sectional nature of the data prevented the understanding and prediction of later suicide risk. There was also possibility of recall bias in this archival retrospective study. In addition, other relevant moderators and mediators of OD and NOD methods such as personality characteristics, coping methods, history of suicide ideation or attempts were not documented. Despite these limitations, our study provides valuable information on the dynamic characteristics of suicide attempts in Singapore, which could help guide the development of policies and intervention methods suited to current trends.