The co-existence of depression and sleep difficulties are very common. Mirtazapine is marketed as a single modality of treatment for both depression and impaired sleep. As a sleep clinic in a psychiatry department, a single modality of treatment for depressive and sleep disorders is preferred by patients and can help improve compliance to treatment. However, there are only 7 published studies investigating the effects of mirtazapine and sleep and these have significant limitations. None of these studies have objectively examined mirtazapine’s short- and long-term on sleep architecture and daytime function (daytime sleepiness, alertness, driving performance) in depressed patients. This study will address these issues.