Why does mirtazapine make you feel sleepy?

Mirtazapine causes sleepiness primarily due to its antihistaminic properties. It blocks histamine H1 receptors, which are involved in regulating wakefulness, leading to sedation. Additionally, mirtazapine increases norepinephrine and serotonin levels, which can also enhance feelings of calm and relaxation, contributing to its sedative effects. As a result, it is often prescribed to help with sleep disturbances in patients with depression or anxiety.