That's not true; I suspect it depends on how many other receptors they hit. One reason Lexapro/escitalopram is liked for its laser precision, in the prescribing information it has the following aside, relevant to receptors it doesn't hit:

"Antagonism of muscarinic, histaminergic, and adrenergic receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular side effects of other psychotropic drugs."