Main findings

We found that people who self-harm are at a greater increased risk of subsequent suicide, particularly in the first year after the index episode of self-harm. Furthermore, the risks of other non-suicide causes of death, particularly accidents, were also elevated. Both suicide and non-suicide mortality risks were particularly high among males. As expected, the highest mortality risk due to non-suicide causes was found among those aged >65 years; whereas for suicide, both middle (45–64 years) and older (>65 years) age groups had higher risk when compared with younger people. Adopting hanging and charcoal burning at the index self-harm episode was associated with a markedly increased risk of later suicide completion; individuals who used these two lethal methods at the index self-harm episode were more likely to use the same method in subsequent completed suicide.

TABLE 2

Method used in the index episode of self-harm and in the subsequent death by suicide among 201 people in Taipei City, 2004–2006, and followed up to 2008

	Men		Women
Method	Index attempt, n	Same method at eventual suicide, n (%)	Index attempt, n	Same method at eventual suicide, n (%)
Solid/liquid poisoning	48	10 (20.8)	68	12 (17.6)
Medicine	36	5 (13.9)	62	9 (14.5)
Pesticide	5	4 (80.0)	1	1 (100.0)
Other poison	7	1 (14.3)	5	2 (40.0)
Wrist cutting	11	0 (0.0)	18	0 (0.0)
Charcoal burning	9	8 (88.9)	10	7 (70.0)
Jumping from a height	0	0 (0.0)	1	0 (0.0)
Hanging	10	8 (80.0)	3	3 (100.0)
Self-mutilation	2	0 (0.0)	3	0 (0.0)
OtherFootnote a	12	3 (25.0)	6	1 (16.7)
Total	92	29 (31.5)	109 23	(21.1)

a. Other categories: domestic gas (n = 4), head banging (n = 2), neck slashing (n = 3), drowning (n = 4), lying on the rails (n = 1), injecting unknown substances (n = 2), swallowing coins (n = 1), other unspecified methods (n = 1).

Strengths and limitations

To the best of our knowledge this is the largest study carried out in a non-Western country investigating mortality outcomes in a cohort of people who self-harm. Based on a city-wide self-harm surveillance system, selection bias is avoided. The strength of the study also lies in its large sample size; hence a wide range of causes of death can be assessed. However, several limitations should be recognised in the interpretation of the current findings. First, valid national identification numbers were not available for 4.6% of the cohort. Those who did not hold a valid identification card may be more likely to be individuals that are more disadvantaged in society (e.g. homeless, foreign brides); their risk of subsequent suicide may be even higher than estimated. However, as they comprised less than 5% of the cohort, our results would not be affected substantially. Second, the cohort included only people whose self-harm act led to an A&E department visit. Individuals who had self-harmed but who did not visit A&E were not included. In addition, some cases of self-harm may not have been registered with the suicide prevention centre: this cannot be ruled out. The incidence of self-harm among males was somewhat lower than that found in Western countries. According to a World Health Organization/EURO Multicentre Project on Parasuicide, the average male suicide attempt rate across European countries was 140 per 100 000 population and the average female suicide attempt rate was 193 per 100 000 population. ^{Reference Schmidtke, Bille-Brahe, DeLeo, Kerkhof, Bjerke and Crepet25}

In addition, detailed information on patient characteristics were not collected in the surveillance database, limiting our ability to control for some potential confounders or to make further analyses. For example, specific psychiatric diagnoses were not recorded and information on suicide intent or treatment were lacking.

Elevated risk of suicide following self-harm

In the first year after the index episode, 1.6% of patients who had self-harmed had killed themselves. After up to 5 years of follow-up, 2.6% of our sample had died by suicide – a 60 times greater risk than that of the general population. More than 60% of the suicides occurred in the first year, approximately 120 times the risk when compared with the general population. Indeed, many prior studies have similarly reported a higher risk in the first year following self-harm. ^{Reference Chen, Tan, Chen, Chen, Liao and Lee12,Reference Yim, Yip, Li, Dunn, Yeung and Miao26,Reference Cooper, Kapur, Webb, Lawlor, Guthrie and Mackway-Jones27} Our figure fell in the middle of an estimate from a systematic review, which reported that the risk of suicide in the first year of follow-up ranged between 0.5 and 2.0%. ^{Reference Owens, Horrocks and House4} Our figure, however, is slightly lower than the 2.0% reported in a recent study from rural Taiwan. ^{Reference Chen, Tan, Chen, Chen, Liao and Lee12} Although the age and gender distribution of the Taipei City sample was very similar to the sample from rural Taiwan, the suicide methods adopted were different. Individuals who self-harm in Taipei City more often take overdoses of medicine (62% v. 43.7%) and few ingest pesticides (1.6% v. 23.6%) compared with individuals in rural Taiwan. ^{Reference Chen, Tan, Chen, Chen, Liao and Lee12} The differences may indicate different characteristics of self-harm populations in these two places; furthermore, pesticide ingestion is associated with a higher case fatality than medicine self-poisoning ^{Reference Gunnell and Eddleston28} and so the higher relative use of pesticides in subsequent episodes in rural areas will contribute to higher subsequent suicide rates. A further explanation for the higher rate of suicide in rural Taiwan could be the lower availability and proximity of emergency treatment in rural areas, which could result in greater fatality.

In keeping with the majority of previous studies ^{Reference Owens, Horrocks and House4,Reference Chen, Tan, Chen, Chen, Liao and Lee12,Reference Hawton, Zahl and Weatherall29–Reference Suokas, Suominen, Isometsa, Ostamo and Lonnqvist31} we found a higher risk of suicide among males who self-harm. In addition, half of the suicides among males occurred within the first 3 months after the index episode of self-harm, suggesting that intensive follow-up for males may be particularly important. However, it should be noted that the SMRs for suicide in males and females who self-harm were elevated to a similar extent at the end of follow-up. Many clinicians may perceive self-harm by females to be less serious than that in males. Our results, however, indicate considerable risk of suicide among females who self-harm.

Most studies have found that suicide risk increases with age among people who self-harm, ^{Reference Nordentoft, Breum, Munck, Nordestgaard, Hunding and Laursen Bjaeldager11,Reference Chen, Tan, Chen, Chen, Liao and Lee12,Reference Hawton, Zahl and Weatherall29,Reference Gibb, Beautrais and Fergusson32} although others have found no difference between age groups. ^{Reference Suokas, Suominen, Isometsa, Ostamo and Lonnqvist31} As the majority (approximately 75%) of people who self-harm are <45 years, large samples are needed to have sufficient power to detect any differences in the risk of suicide between age groups. With our large sample size, we were able to detect an increasing risk of suicide with increasing age. The risk was particularly high in the first 3 months of follow-up. Middle-aged people (45–64 years) have experienced the most dramatic increase in suicide rate in Taiwan. ^{Reference Law, Yip and Chen33} This underlines the need for clinicians to be particularly vigilant for suicide risk in older as well as middle-aged adults presenting with self-harm behaviours.

Similar to studies from Western countries, self-poisoning is the most common method of self-harm in our study sample. However, the proportion of people who used self-poisoning is somewhat lower in our participants (68%), when compared with studies from the West. For example, the proportion of intentional self-poisoning among self-harm cohorts was reported to be 89% and 84% in the UK and Sweden respectively. ^{Reference Hawton, Zahl and Weatherall29,Reference Runeson, Tidemalm, Dahlin, Lichtenstein and Langstrom34} A study from rural Taiwan reported the rate of self-poisoning to be 67%; a figure similar to ours in Taipei City. ^{Reference Chen, Tan, Chen, Chen, Liao and Lee12} Additionally, 5% of individuals who had self-harmed used charcoal burning – this may in part explain the lower rates of solid/liquid poisoning found in our cohort.

Use of hanging and charcoal burning for the index self-harm episode are associated with an increased risk of suicide during follow-up. In addition, the majority of those who subsequently died by hanging and charcoal burning used the same method in their index episode of self-harm. Our results echo a recent study from Sweden that concludes that individuals who use more lethal methods in non-fatal self-harm, including hanging, drowning, using a firearm or jumping from a height, have a greater risk of subsequent suicide. ^{Reference Runeson, Tidemalm, Dahlin, Lichtenstein and Langstrom34}

In contrast to the findings from Sweden, ^{Reference Runeson, Tidemalm, Dahlin, Lichtenstein and Langstrom34} we did not observe an increased risk of subsequent suicide after jumping from a height. It is possible that the majority of individuals choosing to jump from a height as a method of suicide in Taipei City are jumping from their own residential buildings, ^{Reference Chen, Gunnell and Lu35} while in Sweden, jumping from a bridge is more common. Jumping from a bridge usually involves planning (e.g. transportation to jumping site) and hence may indicate a higher level of suicide intent, whereas jumping from a residential building may reflect an impulsive response rather than a strong intent to die. Furthermore, as most suicidal jumps are from high buildings in Taiwan, case fatality is likely to be higher than in Sweden, so the difference with the Swedish study may reflect the differences in characteristics of survivors from jumping suicide in these two places.

No information on suicide intent was available from our cohort. The relationship between the choice of method and suicide intent should be assessed in future studies to better inform the interpretation of case fatality associated with different methods. ^{Reference Hawton36} Our finding indicates that the method of self-harm should be taken into consideration in the assessment of people who self-harm.

Despite differences in patterns of suicide between Taipei City and Western cities, we found many similarities in the risk of suicide among our cohort. The similarities indicate that treatment guidelines or prevention strategies used in the West for individuals who seek medical help after self-harm may be equally applicable in Asia. However, the elevated risk of suicide among those who used charcoal burning in the index episode is worth noting, as charcoal burning is a novel and popular method of suicide in Asia. Current findings further highlight the importance of designing programmes that target this new method of suicide.

Elevated risk of non-suicide mortality following self-harm

An increased risk of mortality in self-harm populations is not due solely to raised rates of suicide. We found that patients who self-harm are at higher risk of mortality from a wide range of causes of death other than suicide. The overall non-suicide mortality risk was higher among men than women. Additionally, the risk was greater in the first year after the self-harm episode. Throughout the course of follow-up, we observed an excess of 4.4 times risk of dying from non-suicide causes when compared with the general population. The increased mortality risk covers a wide spectrum of diseases, including neoplasm, cardiovascular disease, diabetes mellitus, pneumonia, liver and kidney disease, and accidents. These conditions are themselves associated with an increased risk of suicide. ^{Reference Juurlink, Herrmann, Szalai, Kopp and Redelmeier37,Reference Robson, Scrutton, Wilkinson and MacLeod38} Hence, a high proportion of self-harm patients may have pre-existing morbidity. The level of excess risk compared with the general population was higher than the risk observed in the UK ^{Reference Hawton, Harriss and Zahl10} and the USA, ^{Reference Pederson, Tefft and Babigian39} but lower than findings from Scandinavia. ^{Reference Ostamo and Lonnqvist9,Reference Nordentoft, Breum, Munck, Nordestgaard, Hunding and Laursen Bjaeldager11} This difference probably reflects the differences in age distribution of self-harm samples or the variations of baseline disease rates between different countries.

There are several explanations for the excess risk of non-suicide mortality in people who self-harm. First, the medical consequence of the self-harm incident may subsequently increase the risk of death. Second, certain physical disorders (e.g. disease of the gastrointestinal, cardiovascular, endocrine or immune system) may be related to psychiatric disorders ^{Reference Sadock and Sadock40} which in turn increase the risk of suicide. Third, certain characteristics of individuals who self-harm such as impulsivity, risk-taking and alcohol misuse may increase the risk of death due to accidents or liver disease. Last, the presence of physical disease may in itself increase the risk of self-harm behaviours. ^{Reference Juurlink, Herrmann, Szalai, Kopp and Redelmeier37,Reference Robson, Scrutton, Wilkinson and MacLeod38} This explanation is supported by our finding that the non-suicide mortality was extremely high among the elderly – a group that is likely to have a higher prevalence of physical morbidity.

Among all the non-suicide causes of death, the excess risk is highest for accidental death. Similar to suicide, the excess risk is particularly high in the first year after self-harm. In our current analysis, the SMR for accidental poisoning was much higher than other types of accident mortality and was similar to the suicide SMR, indicating the possibility of misclassification of suicide as accident mortality. This observation is consistent with a previous analysis of Taiwanese mortality data that indicated that many accidental poisoning deaths are likely to be misclassified suicides. ^{Reference Chang, Sterne, Lu and Gunnell41}

Clinical implications

The timing of suicide following self-harm and the characteristics of those at greatest risk are broadly similar to those seen in previous studies from Western countries, indicating that strategies developed in the West to reduce suicide risk following self-harm may be applicable in Asia.

Individuals who self-harm are at an increased risk of premature death from suicide as well as other causes. This adds to the overall high risk status of these individuals. Hence, when dealing with patients who self-harm, clinicians should not only assess suicide risk, but also pay attention to their risk of other physical disorders. The first year after the self-harm incident is a critical period, as the risk of death is particularly elevated at this time. Mortality risk is higher for men and for those who are 45 years or over; the heightened suicide risk immediately after self-harm calls for more targeted efforts on this specific age and gender high-risk group.

Assessment of the method used should be a key element of suicide risk assessment. Our results clearly indicate that those who use highly lethal methods of suicide (i.e. hanging, charcoal burning, pesticide ingestion) are more likely to use the same method in any subsequent attempt. Future studies should explore further the reasons of method choice, their relationship with suicide intent and other psychiatric/physical factors to improve the positive predictive value of self-harm behaviours.