Hydroxyzine

The primary effect and the primary side effect. Dose-dependent. This is the mechanism of action for both anxiolysis and insomnia treatment. Tolerance develops with regular use, limiting long-term efficacy as a sedative.

Anticholinergic. Common at standard doses. Usually tolerable in short-term use. Problematic with chronic use, particularly in elderly.

Common, usually mild. Related to CNS depression and possibly mild orthostatic effects.

Anticholinergic. Dose-dependent. Additive with other anticholinergic medications.

Anticholinergic. Particularly relevant in elderly men with prostatic hypertrophy and in patients on other anticholinergics.

Both sedation-based and anticholinergic mechanisms contribute. More pronounced in elderly. A key reason hydroxyzine is on the Beers Criteria list.

Contraindicated in patients with known prolonged QT interval per labeling. Dose-dependent risk. Use caution with concurrent QTc-prolonging medications and in patients with cardiac risk factors or electrolyte abnormalities.

IM administration causes considerable injection site pain. Deep injection into a large muscle (ventrogluteal preferred) reduces but does not eliminate this.

Unlike quetiapine, mirtazapine, or olanzapine, hydroxyzine's H1 blockade at PRN doses does not typically cause significant weight gain. Chronic scheduled use at higher doses could theoretically contribute, but this is unusual in practice.