ADVERSE REACTIONS Side effects reported with the administration of hydrOXYzine hydrochloride are usually mild and transitory in nature. Dry mouth. Anticholinergic: 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. Central Nervous System: In post-marketing experience, the following additional undesirable effects have been reported: Allergic reaction. Body as a Whole: Headache. Nervous System: Hallucination. Psychiatric: Oral hydroxyzine hydrochloride is associated with fixed drug eruptions in postmarketing reports. Skin and Appendages: