This period usually lasts 5 to 8 months after the end of the acute treatment period. The goal at this phase is the prevention of re-lapse. There is a high risk of relapse if treatment is discontinued after the acute treatment phase. The National Institutes of Health Consensus Development Conference on the Mood Disorders (1985) reported a cumulative relapse rate of 15% after 6 months and 22% after 12 months. Keller and colleagues (1982) found that the two best predictors of relapse were a high number of previous depressive episodes (greater than three predicted relapses) and underlying dysthymic disorder.
Once a patient has responded to a medication, the medica-tion should be continued for a minimum of 4 to 6 months, begin-ning from the point of initial response. The World Health Organi-zation (1989) recommended 6 months as a minimum period for continuation of treatment after the acute phase, and the American Psychiatric Association (2000b) recommended a minimum of 16 to 20 weeks of treatment following the full remission of symp-toms. This period should be lengthened for the patient with a his-tory of longer depressive episodes.
Surprisingly, few studies exist that directly look at the effi-cacy of antidepressants for continuation therapy. However, there exists at least one placebo-controlled study for each of the SSRIs (Montgomery et al., 1988, 1993; Montgomery and Dunbar, 1993; Doogan and Caillard, 1992), nefazodone (Feiger et al., 1999) and mirtazapine (Montgomery et al., 1998).
In the past, it was suggested that, on achievement of eu-thymia, doses could be reduced. However, it is more likely that levels similar to those needed at the acute stage of treatment will be required throughout the continuation period.