Although adoption of new modes of self-harm by a population does not occur often, when it does happen it can have an impact on the incidence of suicide in that population (in this article we use the word suicide only to mean death by self-harm, excluding failed attempts at fatal self-harm). Many such changes result from reduced access to a means of suicide. (1) In the United Kingdom of Great Britain and Northern Ireland, for example, the removal of carbon monoxide from the gas supply was associated with a reduction in the overall suicide rate. (2) Introduction of catalytic converters, which reduced the amount of carbon monoxide emitted by car exhausts, was also associated with a fall in the overall incidence of suicide. (3)
Sri Lanka is a developing country that once recorded very high suicide rates. During the period from 1985 to 1989, for example, the national suicide rate for males was the second highest in the world. (4) Before 1960, hanging was the commonest method of suicide in Sri Lanka. In the 1960s, 75% of all suicides by poisoning were caused by ingestion of acetic acid, which was used in rubber processing. (5) The national incidence of suicide rose rapidly between 1970 and 1995 and peaked at 47.0 suicides per 100 000 population in 1995. (6) This increase, which was mainly attributable to pesticide-related deaths, coincided with the increasing pesticide imports that followed the adoption of open economic policies in 1977.
Since 1995 the incidence of suicide has gradually declined in Sri Lanka, (7) although this encouraging trend has gone almost unnoticed. Globally, most suicides in low- and middle-income countries are caused by pesticide poisoning. (8) It is estimated that 300 000 people die annually in Asia from pesticide ingestion. (9) The general means of self-poisoning is very different in high-income countries, where analgesics, tranquillizers and other medicinal drugs are commonly used in overdose. (10) Compared with pesticides, many such drugs are relatively non-toxic. (8) The much higher case fatality rate (CFR) from pesticide poisoning (compared with that of medicinal drug overdose) is a major contributor to deaths from suicide in developing countries. (11,12)
In the absence of any restriction on the availability of the methods previously used, method substitution in self-harm (i.e. the abandonment of one common method of self-harm and its substitution with another method) has not been widely reported. Although, as in many developing countries, pesticide poisoning is a major cause of death in Sri Lanka, (8,13) medicinal drugs were found to be the commonest substances used by the self-poisoning patients investigated at a tertiary care hospital in the city of Colombo in 2007. (14) We set out to investigate recent changes in the methods of self-harm in Sri Lanka--particularly the changes in the methods employed by people attempting suicide--and to explore if such changes could explain the substantial decline in suicide rates.
Data were collected for the period from 1995 to 2009. Data from the records of the Sri Lanka police force were used to calculate annual incidence rates of suicide. As a coroner's inquest is conducted into every unnatural death in Sri Lanka, the police records on suicides were viewed as comprehensive. The data collected were for suicide by any method, suicide by poisoning and suicide by any method other than poisoning. Until the year 2002, when a new coding category was introduced, the cause of large numbers of unnatural deaths was simply classified as "other means" Since the results of previous studies indicate that most such deaths by "other means" were the result of poisoning, (6,15) they were all attributed to poisoning in the present analysis. Annual health statistics from the national ministry of health were used as the source of data on poisoning-related hospital admissions. Estimated mid-year populations for Sri Lanka were used to convert the collected data to annual incidence rates, which throughout this paper are given as the numbers of suicides or admissions for poisonings per 100 000 population. …