Ketamine has been used as an anesthetic for many years. After the 1950s, it was found to have an antidepressant-like effect when used in low doses. Although it is not widely prescribed due to its potential for abuse, studies to unravel its mechanisms of action are quite abundant. In addition to being an antagonist of NMDA and AMPA receptors, it is also effective on monoaminergic and opioid systems. The prominent features of ketamine are that it acts on metabolism in different ways, has a much faster and longer-lasting effect than traditional antidepressants, and especially its performance in patients who are resistant to treatment. R- or S-ketamine enantiomers, or their racemic mixture, have been studied in both preclinical and clinical studies. The conclusion drawn from these studies is that all the properties of ketamine will be elucidated in the coming years and that it will be used as a safe antidepressant for patients suffering from depression.