Pesticide self-poisoning accounts for 14–20% of global suicides, predominantly in agricultural regions where highly hazardous pesticides (HHPs) remain accessible. This poses a critical challenge in South Korea despite its advanced healthcare system. In response, South Korea implemented a phased ban on HHPs, including paraquat, beginning in November 2011. This study aimed to evaluate the long-term effect of this ban on pesticide suicide mortality.

We conducted an interrupted time series study using national mortality data from 2004 to 2023, with autoregressive integrated moving average errors to account for autocorrelation. Sensitivity analyses included alternative intervention timings, period definitions and outcome measures. The primary outcome was the monthly count of pesticide-related suicides.

Among 268,869 suicide deaths recorded during the study period, 34,962 (13.0%) involved pesticide poisoning. The monthly pesticide suicide counts declined from a mean of 244 before the ban to 81 afterwards. The interrupted time series analysis revealed no immediate level change following the ban (−0.204; 95% confidence interval [CI]: −0.989 to 0.581; P = 0.61) but showed a significant acceleration in the decline during the first 36 months (initial slope change: −0.122; 95% CI: −0.163 to −0.082; P < 0.001). Counterfactual projections estimated 10,846 deaths averted (95% CI: −567 to 29,715), representing a 48% model-based reduction. These effects were robust across all sensitivity analyses. Structural breakpoint analysis identified an increase in gas poisoning suicides in August 2008, more than three years before the ban, indicating no evidence of method substitution. The demographic profiles of pesticide and gas poisoning suicides differed substantially.

The ban on HHPs in South Korea was associated with a sustained decline in pesticide suicide mortality over 12 years, with no evidence of method substitution. These findings support the means restriction through pesticide regulation as an effective suicide prevention strategy.