Mirtazapine Onset of Action

Timeline for Clinical Response

The American Psychiatric Association notes that mirtazapine has a statistically significantly faster onset of action compared to citalopram, fluoxetine, paroxetine, and sertraline, with clinical improvement visible within the first 1-2 weeks of treatment 2
Mirtazapine demonstrates clinical improvement within 1-2 weeks of treatment, which is statistically significantly faster than SSRIs, though some patients may experience improvements in sleep and anxiety symptoms within the first week 1, 2

The American Medical Association recommends beginning monitoring of therapeutic response and adverse effects within 1-2 weeks of initiation 2
Treatment should be modified if inadequate response occurs within 6-8 weeks 2
A full therapeutic trial requires at least 4 to 8 weeks to properly assess efficacy 3

Only about 25% of patients become symptom-free after the initial antidepressant trial, and 38% of patients do not achieve treatment response during 6-12 weeks of treatment 1, 2
Many patients require 6-12 weeks for optimal effect 1