There has been considerable interest in the potential of ketamine as a novel antidepressant with a unique mechanism of action. In a number of small trials, ketamine has been shown to lead to reductions in depressive symptoms within hours of administration in patients with symptoms that are otherwise refractory to treatment, with the antidepressant response lasting for days. Although the mechanism of action, as well as the efficacy and safety data, remain to be fully characterised, a number of centres have started to offer ketamine as an off-label treatment for depression. In tandem, a number of larger scale clinical trials are currently underway. At present, it is only advisable to consider the use of ketamine as an off-label treatment for depression in cases where all other treatments have failed, where access to a specialist centre with expertise in the use of ketamine as an antidepressant is available, and where the individual is not suitable to take part in a clinical trial of ketamine.