Optimal dosing schedules for an antidepressant drug can only be established during clinical studies in depressed patients. The benefits of antidepressant therapy are usually progressive, and thus patients must be maintained on a particular treatment for at least 3-4 weeks to assess the efficacy of different doses. Meta-analysis, a widely accepted statistical technique which allows the combination of the results of multiple studies, was used to assess the efficacy of several doses of citalopram over nine placebo-controlled clinical trials. Statistically significant differences between citalopram and placebo were found at both the 20 and 40 mg dose levels. The minimal effective dose of citalopram was shown to be 20 mg. However, analysis of patient subgroups revealed a tendency for those patients suffering from severe or recurrent depression to achieve better results with a higher dosage (40 mg), while patients experiencing their first period of depression or with less severe depression responded well to the minimally effective dose of 20 mg.