Begge mirtazapins enantiomerer menes at medvirke til den antidepressive virkning, S( +) enantiomeren ved at blokere α2 og 5- HT2 receptorerne, og R (-) enantiomeren ved at blokere 5- HT3 receptorerne.
Both enantiomers of mirtazapine are presumed to contribute to the antidepressant activity, the S(+) enantiomer by blocking α 2 and 5-HT2 receptors and the R(-) enantiomer by blocking 5-HT3 receptors.