Evidence of Early Onset of Antidepressant Effect in Randomized Controlled Trials

Although antidepressant medications are effective in approximately 70% of patients with major depressive disorder, they have a delayed onset of therapeutic effect. This latency is problematic in that it prolongs the impairments associated with depression, leaves patients vulnerable to an increased risk of suicide, increases the likelihood that a patient will prematurely discontinue therapy, and increases medical costs associated with severe depression. No adequately designed prospective trials have been conducted to evaluate comparative time to onset of antidepressant effect. However, evidence suggests that some antidepressant agents may begin to work faster than others. Citalopram, venlafaxine, and mirtazapine each have exhibited statistically significant differences in some measures of antidepressant action within the first 2 weeks of treatment, both in placebo-controlled trials and in head-to-head comparisons with other antidepressants. This article reviews the data that hint at these drug-specific differences in time to onset of action. Given the potential benefits of early-acting antidepressant treatments, the possibility of superior speed of onset of citalopram, venlafaxine, and mirtazapine presented here merits further study in adequately designed, prospective clinical trials.