Introduction
Causal inference from observational data remains a significant challenge for scholars and policymakers, particularly in assessing the impact of public health policies where randomization is often infeasible.

Objective
To evaluate the impact of the Yellow September campaign on suicide rates in Brazil using the synthetic control method (SCM).

Methods
A quasi-experimental design was applied using annual suicide rate data from 2000 to 2019. Socioeconomic and demographic variables were obtained from the World Bank and WHO datasets. The SCM was employed to construct a counterfactual scenario simulating suicide rates in the absence of the campaign, using Latin American countries as control units.

Results
The synthetic control model demonstrated a strong alignment between Brazil and its synthetic counterpart in the pre-intervention period. However, post-2015 analysis revealed a 9.2% increase in suicide rates in Brazil compared to the synthetic control. Brazil exhibited a post-/pre-intervention RMSPE ratio of 4.18, the highest among all countries in the donor pool. However, placebo tests indicated that this observed increase was not statistically significant, suggesting the difference may reflect random variation or other factors unrelated to the campaign.

Conclusions
The Yellow September campaign had no statistically significant impact on reducing suicide rates in Brazil. While the observed increase in suicide rates may reflect improved case reporting or contextual influences, these findings underscore the complexity of evaluating mental health policies. Complementary strategies and further research are needed to better understand the campaign's effects and address the multifaceted nature of suicide prevention.