Suicides by firearm are one of major public health issues worldwide [1–5]. Based on the World Health Organization (WHO) 2019 estimates, suicides by firearm caused more than 50,000 deaths in the world in 2019 [1]. The correspondence analysis of the WHO mortality database showed opposite international patterns in preferred suicide methods, and indicated that firearm and pesticide suicides tend to substitute traditional methods, such as hanging, in many countries [6].

In 2016, firearm suicides in the United States of America represented 35.3% of global firearm suicides [2]. Among central European countries, Switzerland has a high rate of suicide by shooting, particularly in men [6,7]. Firearm suicides were widely prevalent in men in Croatia and Serbia, following the civil wars in the 1990s [6,8]. Firearms for suicide were mainly used by men, especially army weapons [2]. International studies show a positive correlation between the rates of suicide by firearm and the availability of and attitudes towards guns [6,9–12].

In Norway, over the 1969–2012 period, firearm suicide rates in males reached a maximum in 1988 (at about 12 per100,000) with an annual change of 4.6%, and then decreased through 2012 (at about 4 per 100,000) with an annual change of −4.8%; in contrast to younger age groups, the increase in the rates of suicides by firearms was observed in the 65 years and over only [13]. The firearm suicide mortality from 1981 to 2018 in Canada had been significantly declining in both sexes, with no significant changes recorded only in recent years among both sexes and across almost all age groups, except the oldest age group (65+ years) [14]. While the trend in firearm suicide in the United States of America was decreasing from 1999 to 2006 by -1.1% per year, from 2006 onwards it showed a significant increase in death rates of +2.0% per year [15]. Additionally, among those aged 5 to 24 years in the United States of America, after a statistically significant decline in suicide mortality from firearms from 1999 to 2007 (by -3.83% per year), subsequently a statistically significant increase in suicide by firearms was noted to 2018 [16]. Changes in the rates and trends of suicide by firearm have been attributed, partly, to adoption of firearms legislation [17,18]. A recent comprehensive review of firearm-control legislation worldwide identified the association between firearm-related laws (regarding restrictions on purchase, access, or use of firearms) and suicide deaths by firearm in certain countries [17]. After the firearm legislation reform in the European Union in 1997, Kapusta and coauthors [19] found that the law was associated with reductions in firearm suicide in Austria (change in trends in pre-/post-law periods = −9.9%). Similarly, Australia’s 1996 gun law reforms were followed by more accelerated declines in suicide mortality by firearm, with the ratio between pre-and post-law trends of 0.954 [20].

Lower socioeconomic status is associated with suicide [21], but this finding was not consistent [22]. According to the Australian national data, there was a positive correlation between suicide rates and Human Development Index values, as a marker of well-being [21]. Naghavi and coauthors found that the Socio-Demographic Index (as a composite measure of income per capita, fertility, and education level) was not associated with firearm suicides [2]. However, research is still lacking to clarify ambiguities regarding the relationships between suicides by firearm and the well-being of a population at the national and global levels.

WHO and the United Nations Sustainable Development Goals (UNSDGs), published in 2015, target to reduce premature mortality from non-communicable diseases by one third by 2030, through prevention and treatment, and promote mental health and well-being [23]. Nevertheless, studies that investigated mortality of suicide by firearm on a global scale are still limited. A better understanding of trends in suicide by firearm can help health service providers and policy makers to identify more effective public health strategies for reducing suicide mortality. The objective of this manuscript was to assess global, regional and national trends in mortality of suicide by firearm. Additionally, this study aimed to evaluate the possible association between mortality of suicide by firearm and some selected measures of human development (Gross Domestic Product—GDP, Gross Domestic Product per capita—GDP per capita, the Human Development Index—HDI).

A total of 1.6 million suicide deaths by firearm occurred worldwide during the observed period (1.4 million among males and 0.2 million among females) (Fig 1). Annually, the number of suicide cases by firearm ranged from 51,241 in 1990 to 55,983 in 1995. A total of 52,694 (45,110 male and 7584 female) suicide deaths resulting from firearms were reported worldwide in 2019.

In both sexes, most suicide deaths by firearm (29,566; 56% of the total) were recorded in the American region, and then in the European Region (8,112; 15%) and South-East Asia Region (7,140; 15%) (Fig 2). The distribution of suicides resulting from firearm are similar for both males and the general population. In females, the highest percentage of suicides by firearm is evident in the American region (3845; 51% of the total), followed by the South-East Asia Region (2084; 27%). Percentage of suicides by firearm among females in the Europe region was three times as low (5%) in comparison to males (17%), while in the South-Asia region it was three times as high (27% vs. 11%, respectively).

The global age-standardized rate of mortality of suicide by firearm was 0.65 per 100,000 persons (Fig 3). The highest rate was found in the American region (2.58 per 100,000), while the lowest rate was reported in the Western Pacific Region (0.05 per 100,000). The global ASR of suicide mortality in 2019 was six-fold higher in males than in females (1.15 per 100,000 in males vs. 0.19 per 100,000 in females). Both in males and females, the mortality of suicide by firearm was the highest in the American region (4.69 per 100,000 vs. 0.66 per 100,000, respectively). Both in males and females, the lowest suicide mortality rates in 2019 were observed in the Western Pacific Region (0.09 per 100,000 and 0.01 per 100,000, respectively).

There are significant variations in the mortality of suicide by firearm between countries by sexes in 2019 (Figs 4 and 5). Mortality rate of suicide in males was the highest in Greenland (24.52 per 100,000), and then the United States of America (10.13 per 100,000) and Uruguay (6.87 per 100,000), followed by populations in Montenegro, Argentina, Venezuela and Lesotho (equally about 5 per 100,000 people), while the lowest mortality rates (0.05 or less per 100,000 people) were observed in Tajikistan, China, Japan and Singapore (Fig 4). The mortality of suicide in females varies greatly across countries: mortality rate was the highest in Greenland (2.69 per 100,000), followed by the United States of America (1.66 per 100,000) and Uruguay (1.30 per 100,000), while the lowest mortality rate (equally 0.01 per 100,000 people) was observed in Republic of Korea, Singapore, Japan, China (Fig 5).

In comparison to males, mortality rates of suicide by firearm were lower in females in all countries across the world in 2019 (S1 Table). Globally, from 1990 to 2019, age-standardized mortality rates of suicide by firearm have a decreasing tendency in both sexes together (AAPC = -2.0% per year). Both in males and females, suicide mortality rates by firearm decreased by AAPC = -2.1%, and by AAPC = -1.6%, respectively. According to the comparability test, suicide mortality trends in males and females were not parallel and not coincident (p<0.05). When mortality trend of suicide by firearm was analyzed by six WHO regions, significantly decreasing trends were observed in males in five regions: in Western Pacific (AAPC = -3.8%), Europe (-3.2%), South-East Asia (-1.9%), Americas (-1.5%), and Eastern Mediterranean (-0.5%); the only exception was the region of Africa, with a stable trend of suicide mortality (+0.3%). Similarly, significantly decreasing trends were observed in females in five regions: in Western Pacific (AAPC = -4.6%), Europe (-3.3%), South-East Asia (-2.3%), Africa (-1.9%), and Americas (-1.3%); the only exception was the Eastern Mediterranean region, with a stable trend of suicide mortality (+0.0%). In both sexes together, 150 out of the total 204 countries and territories across the world showed a significantly decreasing trend in mortality of suicide. Out of all 150 countries with a decline in suicide mortality, Singapore (AAPC = -6.8%), Sri Lanka (AAPC = -5.9%), Australia (AAPC = -5.6%), and Switzerland (AAPC = -5.5%) showed the most marked reductions in mortality rates. A total of 31 countries had a significant increase in suicide mortality, with Jamaica (AAPC = +11.5%) and Lesotho (AAPC = +4.4%) showing the highest increase in mortality. In several countries, suicide mortality trends were significantly increasing in both males and females (in Armenia, Egypt, Eswatini, Jamaica, Lesotho, Libya and Zimbabwe), with the magnitude of the increase mostly higher in females. In some countries a significant increase of trends in suicide mortality was seen only in women, but not in men (in Afghanistan, Antigua, Azerbaijan, Belize, Botswana, Cuba, Lebanon, Mauritius, Morocco, Sudan, Tunisia and Yemen).

Suicide death rates by firearm decreased with age both in males and females (Table 1). In males, suicide mortality rates were almost two times higher in people aged 70 or older than in people under 70, while in females this difference was not observed. Age-specific death rates of suicide by firearm in males were higher than in females in all age groups: difference was about three times in the youngest age group of 10–24 years, while a fifteen-fold higher rate was observed in males than in females in the oldest age group of 70+ years. Suicide mortality by firearm was significantly decreasing in all age groups in both sexes from 1990 to 2019. According to the comparability test, suicide mortality trends by age were not parallel (p<0.05) neither in males or in females.

The linear regression showed significant negative association of global suicide mortality of firearm with HDI, GDP and GDP per capita both in males (R² = 0.984, p<0.001; R² = 0.935, p<0.001; R² = 0.928, p<0.001, respectively) and females (R² = 0.973, p<0.001; R² = 0.906, p<0.001; R² = 0.906, p<0.001, respectively) (S1 Fig).

The Pearson coefficient showed significant positive correlation between mortality of suicide by firearm in males and GDP (r = 0.370) and GDP per capita (r = 0.201) by countries in 2019 (equally both at p<0.01), and absence of correlation with HDI (r = 0.088, p>0.05) (S2 Fig). The significant positive correlation was reported between mortality of suicide by firearm in females and GDP by countries in 2019 (r = 0.403, p<0.01), with absence of correlation with GDP per capita (r = -0.047, p>0.05), while significant negative correlation was noted between mortality of suicide by firearm in females and HDI (r = -0.257, p<0.01).

The present study describes global, regional and national trends of mortality from suicides by firearm across the world during the last three decades. Despite the decreasing trends in mortality of suicide by firearm in most of the areas, observed in both sexes and in all age groups, in 31 countries increasing trends in mortality of suicide by firearm were reported.

In 2019, an estimated total of 52,694 suicide deaths resulting from firearms occurred in the world, with the ASR of 0.65 per 100,000 people in both sexes together. Throughout the whole observed period, suicide mortality rates by firearm were the highest in developed countries (such as the United States of America, France, Canada, Finland, Switzerland, Norway), despite a significant declining trend. At the same time, firearm suicide death rates are over five times higher in the United States of America than they are in other high-income countries. On the other hand, in developing countries (such as Venezuela, Lesotho, Central African Republic, Eswatini, Mozambique) where low mortality rates from suicide by firearm were recorded at the beginning of the observed period, significantly higher rates were recorded in 2019 for both sexes. Marked geographic variations in mortality rates of suicide by firearm could be explained by different prevalence of the main risk factors (such as some socio-demographic characteristics, firearms ownership and availability, large alcohol consumption, comorbidity, etc), and variations in suicide prevention [2,4,32,33]. Besides, it is always a question whether the differences in mortality of suicide by firearm are real or partialy reflect variations in data quality worldwide, in the process of registering causes of death or under-reporting [34,35].

The available literature on the association between firearm-related laws and the rate of firearm-related suicides has reported on studies regarding the legislations and rate of suicide by firearm in high income countries [17–20], mainly in the United States of America [17,18,36]. A longitudinal study of US states from 2012 to 2016, indicated that the total number of firearm laws and Gun Violence Restricting Order laws was negatively associated with firearm-related suicide rate among older adults ages 55–64 and >65 years-old (p<0.001) [36]. In New Zealand, a study which examined national suicide data for 8 years before, and 10 years following the introduction of a more restrictive firearms legislation (Amendment to the Arms Act, 1992) showed a significant decrease in rates of firearm-related suicides, particularly among youth [37]. However, a cross-sectional state-level study in the United States of America showed that not all of the firearm laws were associated with reduced mortality of suicide by firearm: whiles reductions in firearm-related suicide deaths were associated with law that enforced firearm identification and permit processes, the increased suicide rates were associated with three laws and the remaining 20 laws were inconclusively associated [38]. Apart from the variety of laws / the differences in law implementation methods / the diversity in law enforcement efforts / the severity of punishments associated with legal violations / specifics of firearm-related policies across countries, some confounding social and state-level factors act both before and after the respective laws [19,38]. For example, some of the countries with the highest mortality rates of suicide by firearm have the highest social well-being indicators (GDP, GDP per capita, HDI) at the same time (the United States of America, Norway, France, Finland, Canada, Denmark). Also, our study showed a positive correlation between mortality of suicide by firearm in both sexes and GDP in 204 countries and territories worldwide in 2019. In contrast, our study reported a significantly negative correlation only between mortality of suicide by firearms in women and HDI by countries in 2019, which should be evaluate in future epidemiological analytical research.

In this study, men had higher rates of suicide by firearm in all countries, and in all age groups. Epidemiological studies suggested an association between mortality of suicide by firearm and certain socio-demographic characteristics (male sex, middle-age, occupation that provides ready access to firearms such as farmers, farm workers, forestry workers and veterinary surgeons, or active service or retired from the armed services, or the security forces), large amount of alcohol consumption, a recent physical illness, marital problems or a breakdown in relationships [2,39–41]. By contrast, contact with mental health services in the year prior to their death, diagnosis of depression or severe mental illness was not a feature of firearm suicides (this may reflect sex differences in help-seeking) [32,40].

Globally, a substantial decrease in mortality trends of suicide by firearm was observed both in males and females. The decrease in mortality rates of suicide by firearm can primarily be attributed to the decrease in rates in the Americas and European regions (from 7.15 per 100,000 and 2.73 per 100,000 persons in 1990 to 4.69 per 100,000 and 1.33 per 100,000 in 2019 in males, and from 0.99 per 100,000 and 0.16 per 100,000 in 1990 to 0.66 per 100,000 and 0.07 per 100,000 in 2019 in females). But, a total of 31 countries had an increase in mortality of suicide by firearm, although they were mostly less developed countries. Although reasons are not yet well understood, implementation of national guidelines for the suicide prevention only in some countries might, at least partly, explain the observed international differences in mortality rates and trends of suicide by firearm [42]. Numerous studies suggest that restrictive firearm legislation should be an imperative part of a country’s suicide prevention programme [7,9]. The introduction of specific prevention programmes focusing on firearms, such as firearm legislation reform, led to a decrease in suicide rate in the United States of America [15,43], Austria [12], Australia [20]. But, some studies showed opposite findings [17,44]. Some studies, that analized the impact of the Australian Gun Buyback program and the Australian National Firearms Agreement on suicide mortality rates in the Australian population, showed that there was no statistically observable additional impact on suicide mortality attributable to firearms [45,46]. Consequently, although most researchers agree that there is evidence for the effectiveness of restricting access to firearm in prevention of suicide, the above studies suggest that a much more dimensional strategy to reduce firearm-related suicide deaths is needed. A recent study in the United States of America found an association between firearm-related mortality rates among youth and county-level poverty [47]. Some other studies showed that firearms suicide rates were associated with rates of unemployment, low income rates, consumption of alcohol per capita [2,48–50]. Our study showed significant negative association of global trends in suicide mortality of firearm with HDI, GDP and GDP per capita both in males and females. Similarly, findings of other studies confirmed significant negative correlation between economic factors (such as the HDI, GDP per capita, GINI index) and suicide rates in both genders [51–53].

Therefore, the differences between the regional and national rates and trends in mortality of suicide by firearm indicate further possibilities for reducing suicide mortality and the need for a more effective public health approach to prevention of suicide across the world.

There are large international differences in the mortality patterns of suicide by firearm. Despite the decreasing trends recorded in both sexes in most countries in the world from 1990 to 2019, the suicide by firearm showed an increasing trend in some countries. Future research should investigate the factors which have contributed to substantial geographic variations in mortality of suicide by firearm in order to determine more effective ways to further reduce mortality in suicide by firearm.