There is little evidence that medical transition decreases suicidality.
When it comes to gender dysphoric children, there is little evidence that medical transition decreases suicide rates. There is little evidence to assert that puberty blockers are necessary to prevent suicide .
After sex reassignment surgery, one study showed that adult transsexual clients were 4.9 times more likely to have made a suicide attempt and 19.1 times more likely to have died from suicide, after adjusting for prior psychiatric comorbidity . Similarly, an Australian paper  notes that many patients have poor outcomes which put them at risk of suicide.
A prominent study  claiming that medical transition alleviated suicidality had to be corrected , to clarify that it proved “no advantage of surgery” in this regard.
A long-term Swedish study  finds that post-operative transgender people have “considerably higher risks” for suicidal behavior.
Similarly, a study in the European Journal of Endocrinology  demonstrates that suicide rates among transgender male-to-females were 51% higher than the general population.
 Biggs, M. (2020). Puberty Blockers and Suicidality in Adolescents Suffering from Gender Dysphoria. Archives of Sexual Behavior (49): 2227–2229. [Link]
 Zucker, K.J., Lawrence, A.A., Kreukels, B.P. (2016). Gender Dysphoria in Adults. Annu Rev Clin Psychol. 12: 217-47. [Link]
 D’Angelo, R. (2018). Psychiatry’s ethical involvement in gender-affirming care. Australasian Psychiatry 26 (5): 460-463. [Link]
 Bränström, R. & Pachankis, J. E. (2019). Reduction in Mental Health Treatment Utilization Among Transgender Individuals After Gender-Affirming Surgeries: A Total Population Study. American Journal of Psychiatry 177 (8): 727-734. [Link]
 American Journal of Psychiatry (2020). Correction to Bränström and Pachankis. Published online: 1 August 2020. [Link]
 Dhejne, C., Lichtenstein, P., Boman, M., Johansson, A. L. V., Långström, N., & Landén, M. (2011). ‘Long-term follow-up of transsexual persons undergoing sex reassignment surgery: Cohort study in Sweden’. PLoS ONE, 6(2). [Link]
 Asscheman, H., Giltay, E. J., Megens, J. A. J., de Ronde, W., van Trotsenburg, M. A. A. & Gooren, L. J. G. (2011). A long-term follow-up study of mortality in transsexuals receiving treatment with cross-sex hormones. European Journal of Endocrinology 164 (4). [Link]