Mirtazapine and Slow-Wave Sleep: A Focused Narrative Review of Human Polysomnographic Evidence

Sleep disturbance is a common feature of depressive disorders and may be influenced by antidepressant-associated alterations in sleep architecture. Mirtazapine is a noradrenergic and specific serotonergic antidepressant with a distinctive pharmacologic profile involving histamine H1 receptor antagonism, alpha-2 adrenergic antagonism, and serotonergic receptor modulation, which may contribute to its effects on sleep regulation. This focused narrative review examines the neurobiological mechanisms through which mirtazapine may influence sleep architecture and summarizes available human polysomnographic (PSG) evidence, with particular emphasis on N3 sleep and slow-wave sleep-related measures. Current evidence suggests that mirtazapine can produce measurable changes in objective sleep architecture; however, findings specifically regarding N3 sleep and slow-wave sleep remain preliminary and mixed. Available studies are limited by small sample sizes, heterogeneous populations, variable treatment durations, differences in comparator conditions, and methodological variability. Although selected studies have reported increases in slow-wave sleep measures or N3 sleep, available evidence does not establish a consistent dose-response relationship or demonstrate that sedative effects directly translate into enhancement of slow-wave sleep. Mechanistic evidence supports several biologically plausible pathways through which mirtazapine may influence sleep regulation, including histaminergic, adrenergic, and serotonergic effects; however, human PSG studies evaluate the integrated effects of the complete medication and cannot establish receptor-specific mechanisms responsible for observed sleep changes. Future studies using standardized PSG protocols, quantitative electroencephalography (EEG) analysis, larger samples, longer treatment durations, and direct dose comparisons are needed to clarify whether mirtazapine-associated alterations in sleep architecture contribute meaningfully to clinical outcomes.