ADVERSE REACTIONS Side effects reported with the administration of hydroxyzine hydrochloride are usually mild and transitory in nature. Anticholinergic Dry mouth. Central Nervous System Drowsiness is usually transitory and may disappear in a few days of continued therapy or upon reduction of dose. Involuntary motor activity including rare instances of tremor and convulsions have been reported, usually with doses considerably higher than those recommended. Clinically significant respiratory depression has not been reported at recommended doses.