Table 4.

Potential adverse effects of first-generation antihistamines.²

Action site	Effect
H1 receptor in central nervous system	Sedation and decreased attention, cognition, learning, memory and psychomotor performance
Muscarinic receptor	Dry mouth and eyes, urinary retention, sinus tachycardia, mydriasis, and constipation
Serotonin receptor	Increased appetite and weight gain
Alpha-adrenergic receptor	Dizziness and postural hypotension
Cardiac ion channels	Increased QT interval and ventricular arrhythmia

Adapted from Simons and Simons.²