This systematic review and quantitative meta-analysis, published in General Hospital Psychiatry, evaluates ketamine's efficacy as a novel treatment for major depressive disorder and bipolar depression. Analyzing randomized placebo-controlled trials, the study reveals that ketamine significantly reduces depressive symptoms, with substantial effects evident from day 1 and sustained at least a week post-infusion. The findings demonstrate ketamine's rapid onset, high efficacy, and good tolerability, offering new hope in the pharmacotherapy of depression and bipolar disorders. This comprehensive analysis underscores ketamine's potential as a groundbreaking intervention in mental health treatment.