They possess anticholinergic effects
(except the “nonsedating” agents: astemizole, azelastine, cetirizine,
desloratadine, fexofenadine, loratadine, and terfenadine). They may also
stimulate or depress the CNS, and some agents (eg, diphenhydramine) have
local anesthetic and membrane-depressant effects in large doses.