Side Effects of Hydroxyzine
Hydroxyzine commonly causes drowsiness and dry mouth, with serious but rare cardiac risks including QT prolongation and torsade de pointes, particularly concerning in elderly patients who may also experience cognitive decline from its anticholinergic effects 1.
Common Side Effects
The most frequently reported adverse effects are typically mild and transitory 1:
- Drowsiness/sedation - Usually transitory and may disappear within a few days of continued therapy or with dose reduction 1. This was reported in 28% of patients in clinical trials 2
- Dry mouth - Due to anticholinergic properties 1
- Weight gain - Reported in approximately 12% of patients 2
- Loss of concentration - Occurs in about 9% of patients 2
Serious Cardiac Risks
Cardiac toxicity represents the most concerning adverse effect profile:
- QT prolongation - Well-documented in post-marketing surveillance 1
- Torsade de pointes - A potentially fatal ventricular arrhythmia that can occur even at therapeutic doses 1, 3
- Healthcare providers should conduct baseline ECG monitoring, especially in high-risk patients, and avoid concurrent use with other QT-prolonging medications 3
Neurological Effects
- Involuntary motor activity including tremor and convulsions - Usually occurs only with doses considerably higher than recommended 1
- Headache - Reported in post-marketing experience 1
- Hallucinations - Rare psychiatric effect 1
- Cognitive decline - Particularly worrisome in elderly populations due to anticholinergic effects 4
Dermatological Reactions
- Acute Generalized Exanthematous Pustulosis (AGEP) - Serious skin reaction reported in post-marketing surveillance 1
- Fixed drug eruptions 1
- Pruritus, rash, urticaria - Paradoxically, despite being an antihistamine 1
Important Clinical Distinctions
Hydroxyzine produces fewer antimuscarinic effects compared to diphenhydramine 5. In a large cohort analysis, hydroxyzine-poisoned patients were less likely to develop classic anticholinergic toxidrome features and more likely to present with mild CNS depression rather than antimuscarinic findings 5. This is consistent with hydroxyzine's receptor binding profile.
Overdose Manifestations
The most common manifestation is hypersedation, with other signs including convulsions, stupor, nausea, and vomiting 1. Overdose may cause QT prolongation and torsade de pointes, requiring ECG monitoring 1.
Special Population Concerns
Elderly patients warrant particular caution due to increased risk of cognitive decline from anticholinergic effects 4. The combination of sedation, cognitive impairment, and cardiovascular risks makes hydroxyzine especially problematic in this population 4.
Tolerability Profile
In controlled trials, side effects were reported in 52% of hydroxyzine patients versus 35% with placebo 2. However, hydroxyzine demonstrated equivalent acceptability and tolerability compared to benzodiazepines and buspirone in GAD treatment 6. The sedative effects typically diminish with continued use 2.