Mirtazapine has antihistamine, α2-blocker, and antiserotonergic activity.[1][75] It is specifically a potent antagonist or inverse agonist of the α2A-, α2B-, and α2C-adrenergic receptors, the serotonin 5-HT2A, 5-HT2C, and the histamine H1 receptor.[8][75] Unlike many other antidepressants, it does not inhibit the reuptake of serotonin, norepinephrine, or dopamine,[8][75] nor does it inhibit monoamine oxidase.[76] Similarly, mirtazapine has weak or no activity as an anticholinergic or blocker of sodium or calcium channels, in contrast to most TCAs.[8][4][75] In accordance, it has better tolerability and low toxicity in overdose.[8][77] As an H1 receptor antagonist, mirtazapine is extremely potent, and is in fact the most potent of all the TCAs and TeCAs.[6][78][79] Antagonism of the H1 receptor is by far the strongest activity of mirtazapine, with the drug acting as a selective H1 receptor antagonist at low concentrations.[8][69]