An analysis of secular trends in method-specific suicides in Japan, 1950–1975

In this research, we investigated the method-specific suicide trends by age and gender in Japan in the 1950s and 1960s. A rapid rise in suicide rate was observed in the 1950s, and then the rate decreased just as rapidly in the 1960s. The change in the suicide rate during this period was more marked among people aged 15–29 years compared to those aged 30–49 and 50 years or over. Poisoning by solid and liquid substances overwhelmingly contributed to the dramatic change in the overall suicide rates in males and females aged 15–49 years in the 1950s and 1960s. For the peak years of the rise in poisoning suicides, bromide was the most frequently used substance. The results of our research show that assessing secular trends in method-specific suicides by gender and age can contribute to a deeper understanding of the dramatic increase and decrease in the overall suicide rate in Japan in the 1950s and 1960s. Although rapid increases or decreases in suicide rates have been also observed in some countries or regions recently (e.g., South Korea, China), trends in method-specific suicides have not been analyzed because of a lack of data on method-specific suicide in many countries. Our study illustrates how the collection and analysis of method-specific data can contribute to an understanding of dramatic shifts in national suicide rates.

The study had several limitations that deserve discussion. First, although the data used in this analysis are based on data from official death certificates, completeness of suicide death recording may have changed over time as stigma associated with suicide could have changed. Moreover, changes occurred in the ICD classification system over the time period studied. However, visual inspection of the figures revealed no obvious discontinuities in the overall and method-specific suicide rates in the years when successive revisions of the ICD were implemented in Japan. We think that these changes could not fully explain the dramatic change in the suicide rates among young Japanese in the 1950s and 1960s. Second, we obtained data on the specific solid/liquid substances used in suicides for only a limited set of years. However, since we obtained data for the years between 1958 and 1967, we were able to observe a sharp decrease in the rate of poisoning suicides from the peak. Therefore, we clarified what kind of solid/liquid substances were the most frequently used in the peak years and how the mortality rate due to each of the substances changed. Last, the study was descriptive in design, and the delineation of the complex relationships among risk factors for suicide was beyond the scope of this study.

Motohashi examined the effects of socioeconomic factors on secular trends in suicide rates in Japan for the period 1953–1972 [10], and the result was that the suicide trends were almost parallel to those of unemployment rates in both men and women. However, if the socioeconomic factors in the 1950s and 1960s had influenced all method-specific suicides, all of the rates would have changed in a similar way. Actually, the changes in all method-specific suicide rates other than solid and liquid poisoning were less marked during this period. Thus, we think that socioeconomic factors do not fully explain why the drastic changes in overall suicides were observed in the 1950s and 1960s.

Bromide was the most frequently used substance of all liquids/solids among males and females aged 15–29 and 30–49 years in the peak years of the poisoning suicide rates. In Japan, bromide, the product name of which was “Calmotin,” had been available as an over-the-counter medicine by the early 1930s at the latest, and was commonly used as a hypnotic and sedative [16, 17]. Thus, easy access to this drug could lead to a large number of suicides due to this drug. Other analgesics were the second-most frequently used substance category among males aged 15–29 and 30–49 years and females aged 15–29 years in the late 1950s. Meprobamate was a carbamate derivative used as an anxiolytic drug and included in the category “other analgesics.” This drug was sold as an over-the-counter medicine in Japan starting in 1957 [18]. It was suggested that drug companies’ advertisements and mass media reporting could lead to an increase in users of the drug and suicides due to the drug [18]. This social circumstance, combined with the socioeconomic crisis after the war, might have led to the dramatic increase in poisoning suicides in the 1950s.

The Pharmaceutical Affairs Law (Act No. 145 of 1960), which was a law regulating the manufacturing, importation, and sale of drugs and medical devices in Japan, went into effect in February 1961 [19]. This law classified most hypnotics and sedatives, including bromisoval (Calmotin) and meprobamate, as habit-forming drugs and regulated the sale of these drugs. In addition, the Agricultural Chemicals Control Act (Act No. 82 of 1948) and Poisonous and Deleterious Substances Control Act (Act No. 303 of 1950) were promulgated in July 1948 and December 1950, respectively. These acts were established for the purpose of strengthening regulations on the production, import, sale, and handling of pesticides, cyanide, or other poisonous substances. These regulations may have been effective in the prevention of misuses of these substances only after the mid-1950’s and thus may have contributed to a decrease in suicides by these substances.

The changes in suicide rates due to poisoning by solid and liquid substances during the 1950s and 1960s were much more marked for younger Japanese than for older groups. One explanation for this age difference is that youth are more likely to imitate societal trends and to attempt copycat suicides. For example, there was a major rise in hanging suicides in young Australian men and women in the 1980s [2].

Choice of suicide methods is not likely to be random, but rather influenced by a complex constellation of psychosocial, environmental, and biological factors which precede the decision to commit suicide [2]. Physical availability and sociocultural acceptability are viewed as two key factors that influence the choice of suicide method [20]. Physical availability refers to the extent to which a particular method of suicide is accessible to the individual, while sociocultural acceptability is a measure of the extent to which a person’s choice of method is shaped and circumscribed by the norms, traditions, and moral attitudes of their culture. There is good evidence that changing the physical availability of lethal methods is an important contributor to suicide rates [2, 3]. Previous research has shown that method-specific suicide rates decreased after firearm control legislation, restrictions on pesticides, and detoxification of domestic gas [5, 21‐23]. In countries where a particular method is common, restriction of that means could also lead to lower overall suicide rates [3, 24]. Means restriction is most effective when the method is common and highly lethal [3]. Although substitution of one method with another does happen, people who attempt suicide with less lethal means have an increased chance of survival when reduced access to a highly lethal method is possible. The present study revealed that in Japan during the 1950s and 1960s, the legal restrictions on access to medical drugs and poisonous substances resulted in dramatic falls in suicide rates, especially among the young population, and confirmed that modification of the environment to restrict access to lethal means was a key element of suicide prevention efforts [1, 3, 24]. Since devising appropriate restriction policies requires a detailed understanding of the methods of suicide used in the community (as well as of the method preferred by different demographic groups within the community) [1], detailed research on the descriptive epidemiology of suicide will continue to be relevant.