The transgender population in the world has been investigated by many different studies. Determining their exact number both in terms of prevalence and occurrence depends on the basic definition but according to a systematic review published in 2016, approximately 9.2 out of every 100,000 people in the world were transgender [12]. These results show the study of these populations and factors affecting health outcomes such as their socioeconomic status is very important. This study was a systematic review and meta-analysis conducted with the aim of accurately determining the prevalence of suicidal thoughts and attempts among transgender people in the world, in which the lifetime prevalence of suicidal thoughts and attempts in transgender people was 50% and 29%, respectively. These results prove the fact that almost half of the transgenders who have suicidal thoughts commit suicide. These results are very important for health policy makers and health decision-makers in the world, especially in the developing countries, because it shows the lack of proper efficiency and effectiveness of health, educational and therapeutic interventions to prevent suicide attempts and successful suicide in the transgender community. Various factors, including economic, social, cultural, health and medical factors play a role in increasing the prevalence of suicidal thoughts and, of course, suicide attempts.

On the other hand, the results of past studies have shown transgender people are at a higher risk of experiencing suicidal thoughts during their lifetime compared to other gender minority populations such as bisexuals and MSM (50% vs. 23% and 34%, respectively). This indicates compared to other sexual minorities, there are other factors which put transgender people at greater risk of suicidal thoughts and actions [13, 14]. Among the important influencing factors, we can mention the costs related to hormone therapy and how to access it, taking into account the space and environment of providing hormones, as well as direct and indirect costs related to it. Transgenders, whether FTM or MTF, need to receive sex hormones, especially estrogen or testosterone, for a long time and before performing any related surgery in order to establish their desired gender identity in their society, family and peers. The results of past studies have shown hormone therapy among transgender people causes beneficial effects such as strengthening psychological function and reducing depression and anxiety but it should be kept in mind that various factors have an effect on it. Some transgender people may be deprived of this type of treatment and access to it due to lack of financial ability, social stigma and discrimination, fear of gender identity disclosure and sexual and work abuse. As a result of this problem, they suffer from complications such as depression and anxiety disorders and suicidal thoughts leading to commit suicide [15,16,17,18,19].

In order to supply the required hormones in this society, which is considered one of their most important needs in the process of gender change, economic obstacles and problems can be considered as the most important factor in access to hormones. To solve this challenge, basically, there are two ways ahead of transgender people. First, these people have the support of their family and friends; in this case, the main challenge is the existence of stigma and discrimination in centers providing care or treatment services, such as pharmacies, hospitals, or care centers. Second, they do not have the support of their family and friends, and in other words, they have been rejected by them. In this case, they face economic problems and the existence of stigma in order to provide the needed hormones in the service centers. In the first case, transgender people, due to lack of direct access to needed hormones or other essential services, are forced to spend exorbitant economic costs to indirectly access the drugs they need. In the second case, these people are forced to find a job and create a source of income in order to cover the costs required for the provision of medicines and services. In this case, the possibility of work and sexual abuse of these people is very high. In both cases, these people are exposed to diseases and mental disorders such as depression, anxiety, seclusion and loneliness [19,20,21,22,23,24], because receiving the required hormones and necessary treatments in gender minorities especially transgender is one of the important factors in suicide prevention [25,26,27]. The results of past studies have shown the presence of mental disorders such as anxiety and depression in gender minorities, especially transgenders, is the main cause of suicide. Also, the results of these studies have shown due to the existence of these mental disorders, the rate of suicide in homosexuals and heterosexual people who have homosexual behavior is higher than that of heterosexual ones [28,29,30].

Among other worrisome cases, we can mention the high prevalence of drug use among these people so that according to reports, lifetime use of drugs such as cocaine, heroin and methamphetamines in these people was 27.1%, 26.1%, 24.9%, respectively, which can cause an increase in suicide attempts by these people. One of the risk factors exposing these people to drug use is their victimization of violence, rejection from society, family and surrounding people, and lack of access to needed facilities due to stigma and discrimination [31, 32]. On the other hand, these people are forced to have sex at a young age in order to meet their living expenses and find trust and support from the people around them. According to the results of past studies, transgender students are more likely than cisgender ones to experience the first sex before the age of 13 years and to have more than four sexual partners [31,32,33,34]. These early sexual experiences can expose these people to emotional damage caused by relationships, an increase in the risk of sexually transmitted infections and finally the occurrence of mental disorders and suicide.

Gender minorities, especially transgender people, face unique challenges and discrimination, such as high rates of institutionalized prejudice, bullying, violence, and physical attacks. Exclusion from the family, stigma and discrimination and other social factors expose transgender people to a phenomenon called internalized transphobia and a negative self-concept related to their gender identity. These feelings can include self-loathing or shame. Internalized transphobia increases the likelihood of suicide attempts in the transgender population [35,36,37].

Subgroup analyzes in the present meta-analysis showed the prevalence of suicidal thoughts in the trans community living in Asia was higher than that of other continents. This difference can be attributed to differences between various cultures and fixed traditions in families. In some Asian societies, such as Thailand, despite social supports, transgender people do not have a favorable acceptance in their families, which can be attributed to the existence and stability of traditional cultures in the family after several years [38]. However, the prevalence of suicide attempts in the trans community living in Australia and Oceania was higher than those of other continents. Based on the meta-analysis findings, the prevalence of suicidal thoughts in the FTM trans community in the Asian and American continents was higher than that of the MTF trans community. This may be due to the fact that in these communities, FTMs experience more victimization than MTFs and have more lifetime suicidal ideation [39]. Also, living more in stigmatizing communities can facilitate vulnerability to experiencing stigma-related stressors, which increases suicidal thoughts and attempts among FTM trans people [40]. In general, the prevalence of suicide attempts in the MTF trans community was higher than that of the MTF trans community. Previous studies have shown sexual abuse rates were higher among MTF individuals, which was significantly associated with suicide [41]. Among those known as transgender, men are consistently at higher risk of suicide than women [41]. Also, based on previous studies, trans-men report higher levels of gender discrimination compared to trans-women [42, 43].

In this study, the primary target group is transgender individuals, who are considered one of the key and high-risk populations in society. This group, along with other groups such as lesbian, gay, and bisexual, fall under the umbrella of the LGBT community (lesbian, gay, bisexual, transgender and queer people). These groups differ from each other in terms of high-risk behaviors, susceptibility to viral diseases and infections such as Hepatitis B (HBV) and C (HCV), or human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS). Of course, considering their different circumstances, they also differ in terms of susceptibility to physical and mental disorders. For example, in terms of the degree of social discrimination and intolerance, these individuals face varying degrees of it, which may have an impact on the development of mental disorders and ultimately suicide. All previous studies have two comprehensive limitations. First, they have not been conducted on a specific group of LGBT individuals. This means that they have considered all of these groups as a single entity and reported the prevalence and incidence outcomes in this group as a whole, without paying attention to the differences between these groups [44,45,46,47].

The second limitation is that the published studies have mainly focused on the risk or tendency towards suicide ideation or attempts in these communities, rather than the actual prevalence and incidence of suicide. For example, a study by Mattia Marchi and colleagues [47] has specifically examined the risk of suicide attempts in LGBT communities. However, determining the exact prevalence of suicide, especially among transgender individuals, is of utmost importance for allocating healthcare services and providing necessary care in this community.

In addition, suicide can be categorized into two forms; suicide ideation and suicide attempts, and both should be investigated. However, in previous published studies, this aspect has received less attention. In the current meta-analysis, this issue has been analyzed and reported.

Other strengths of the present meta-analysis are the large number of analyzed cross-sectional studies and the subgroup analyzes based on the important variables reported in the primary studies. This can be effective in applying the present meta-analysis results to compile and allocate health services and care programs for the transgender community in different countries. In addition, the present meta-analysis results can be considered as a warning to health policy makers and health decision-makers in different countries because these results show the prevalence of suicidal thoughts and attempts in the transgender community is high and all health measures, interventions and treatment in this field should be reviewed and reformulated. On the other hand, these results for researchers and clinical researchers can open the way for more research with better ideas in the field of suicide in transgender people.

Among the limitations of the present study, we can mention the small number of studies in some countries such as Australia, which can make it possible to overestimate the overall result due to the small number of analyzed studies. Therefore, it is suggested to design and conduct survey studies with an appropriate sample size in these countries, considering all transgender groups in society in order to determine suicide prevalence.