Ketamine has emerged as a promising treatment for suicidal ideation (SI) in patients with major depressive disorder (MDD), showing rapid and sustained reductions in suicidality. Studies from 2020–2025 found IV ketamine and esketamine significantly decreased SI for days to weeks, with early responders showing lower suicide risk at three months. While its mechanisms—such as reduced lateral habenula activity—are still being studied, ketamine must be used alongside therapy, monitoring, and comprehensive psychiatric care to ensure safety and effectiveness.