Hydroxyzine
First-generation sedating antihistamine (H1 antagonist) prescribed for anxiety, pruritus, and as a non-habit-forming sleep aid. Reliably sedating and non-scheduled, but anticholinergic, causes next-day drowsiness, and carries a dose-dependent QT-prolongation warning.
01 Overview
Hydroxyzine (brands Atarax, Vistaril) is a first-generation piperazine H1 antihistamine used for anxiety, itch, and as a sedative/hypnotic. Because it is not a controlled substance and does not cause dependence, it is often chosen for sleep and anxiety in patients where benzodiazepines are best avoided, including those with substance-use histories.
At bedtime doses it reliably produces sedation via central H1 blockade. Downsides are the familiar first-generation antihistamine profile: anticholinergic effects, next-day grogginess, and, importantly, a dose-dependent risk of QT-interval prolongation that led regulators to caution against high doses and use in patients with cardiac risk factors.
02 Mechanism
Central and peripheral histamine H1 receptor antagonism produces sedation and anxiolysis; also has anticholinergic activity and some 5-HT2 antagonism.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Sedation / sleep | 25–50 mg | Oral | 25-50 mg at bedtime; up to 100 mg used for anxiety/pre-op. Lower doses in the elderly. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Sedation / reduced sleep onset latencyReliably induces drowsiness and shortens time to sleep. | Clinical | ||
| AnxiolysisReduces anxiety without the dependence risk of benzodiazepines. | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Next-day sedation / anticholinergic effectsDaytime drowsiness plus dry mouth, constipation, and blurred vision. | Moderate | Common | Clinical | |
| QT-interval prolongationDose-dependent QT prolongation with a risk of torsades de pointes. | Severe | Rare, dose-dependent | Clinical |