Objectives This study examined the shifts in the suicide trends in Korea during the initial phase of the Fifth Master Plan for Suicide Prevention, using interrupted time series analyses. Methods Interrupted time series analyses were performed using the monthly suicide data from January 2011 to April 2024. Quasi-Poisson regression models were applied to evaluate the changes in the level and slope of the suicide trend before and after policy implementation. The Autoregressive Integrated Moving Average (ARIMA) and Prophet models were used to compare the actual and predicted counterfactual numbers of suicides during the policy period. Results The quasi-Poisson regression model revealed a significant change in the trend of suicides among men, with an increasing slope during the policy period. For total suicides, the ARIMA and Prophet models suggested that the actual number of suicides was significantly higher than the counterfactual number during the policy period, with excess suicides averaging between 113 and 150 per month. The actual number of suicides among men was significantly higher than the counterfactual number during the policy period, with excess suicides averaging between 86 and 92 per month. No significant changes in the suicide trends among women were observed. Conclu...