This suggests that ketamine may have a chronotherapeutic effect, which is in keeping with recent theories of ketamine’s effects on the timekeeping of the central clock and alteration of the synchronization to external light cycles.51 It has been suggested that circadian changes represent a long-term downstream stabilization effect in mood disorders.29 A larger sample population and a further period of study beyond the endpoint used (1 week after the eighth treatment) may be needed to observe further chronotype changes. Here, CLOCK is linked to mood disorder.