B. Mirtazapine mechanism

This drug enhances serotonin and norepinephrine neurotransmission via mechanisms related to its ability to block presynaptic α2 receptors. Additionally, it may owe at least some of its antidepressant activity to its ability to block 5-HT2 receptors. It is a sedative because of its potent antihistaminic activity, but it does not cause the antimuscarinic side effects of the TCAs, or interfere with sexual functioning, as do the SSRIs. Increased appetite and weight gain frequently occur. Mirtazapine is markedly sedating, which may be an advantage in depressed patients having difficulty sleeping.