Major depressive disorder has a high prevalence globally. Although pharmacotherapy and psychotherapy are effective for most patients, about one third is treatment resistant. Ketamine, known as an anesthetic, is a new treatment option that can be effective in patients with treatment-resistant depression. (es)ketamine works relatively fast. However, the long-term effects are still relatively unknown. In the Netherlands, S-Ketamine is currently administered in various forms, of which only the nasal spray is registered for treatment-resistant depression. Currently, many studies have been conducted on the use of (es)ketamine. In this article we describe the latest state of affairs regarding its effectiveness and safety.