Hydroxyzine (Vistaril / Atarax)
First-generation antihistamine (H1 antagonist) and 5-HT2A antagonist used for anxiety, pruritus, and preoperative sedation. Crosses the blood-brain barrier producing anxiolytic and sedative effects. Metabolized by CYP3A4 to cetirizine (Zyrtec), an active but peripherally-restricted antihistamine. No dependence potential or withdrawal, making it a preferred PRN anxiolytic alternative to benzodiazepines.
Projected serum levels — 25 mg, twice daily
Maintenance schedule: 25 mg twice daily (oral).
Loading schedule: 75 mg on day 1, then 25 mg twice daily — reaching therapeutic levels sooner.
Modeled steady state after ~3 days: peak ≈ 57.5 mg, trough ≈ 41.1 mg body load. Population-based estimate over 15 days for a 25 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.
Key facts
- Category
- Anxiolytic
- Route modeled
- Oral
- Model confidence
- predicted
- Half-life
- 20 h
- Common dose
- 25 mg
- Suggested maximum
- 100 mg/day
- Reference dose range
- 12.5–100 mg (single dose)
- Suggested cadence
- twice daily
- Validated against
- 25 mg oral — Cmax 0.072 mg/L at 2 h
Documented interactions
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contraindicated
Efavirenz (Sustiva) + Hydroxyzine (Vistaril / Atarax)
Efavirenz (Sustiva) inducer of CYP3A4 predicted to change Hydroxyzine (Vistaril / Atarax) AUC by ~0.16x
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contraindicated
Rifampin + Hydroxyzine (Vistaril / Atarax)
Rifampin inducer of CYP3A4 predicted to change Hydroxyzine (Vistaril / Atarax) AUC by ~0.16x
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danger
2C-B (4-Bromo-2,5-dimethoxyphenethylamine) + Hydroxyzine (Vistaril / Atarax)
2C-B (4-Bromo-2,5-dimethoxyphenethylamine) and Hydroxyzine (Vistaril / Atarax) both have serotonergic activity. Risk of serotonin syndrome (hyperthermia, rigidity, autonomic instability, altered…
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danger
4-AcO-DMT (Psilacetin) + Hydroxyzine (Vistaril / Atarax)
4-AcO-DMT (Psilacetin) and Hydroxyzine (Vistaril / Atarax) both have serotonergic activity. Risk of serotonin syndrome (hyperthermia, rigidity, autonomic instability, altered mental status).
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danger
5-MeO-DMT (5-Methoxy-N,N-dimethyltryptamine) + Hydroxyzine (Vistaril / Atarax)
5-MeO-DMT (5-Methoxy-N,N-dimethyltryptamine) and Hydroxyzine (Vistaril / Atarax) both have serotonergic activity. Risk of serotonin syndrome (hyperthermia, rigidity, autonomic instability, altered…
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danger
6-APB (Benzofury / 6-(2-aminopropyl)benzofuran) + Hydroxyzine (Vistaril / Atarax)
6-APB (Benzofury / 6-(2-aminopropyl)benzofuran) and Hydroxyzine (Vistaril / Atarax) both have serotonergic activity. Risk of serotonin syndrome (hyperthermia, rigidity, autonomic instability, altered…
Serum checks 190 modeled interaction pairings for hydroxyzine (vistaril / atarax) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.
Research behind this entry
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Hydroxyzine in generalized anxiety disorder: a double-blind comparative study versus placebo and buspirone
Multicenter RCT (244 GAD patients) demonstrating hydroxyzine 50 mg/day was significantly superior to placebo and comparable to buspirone 20 mg/day for anxiety reduction, with rapid onset within 1 week.
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Pharmacokinetics of hydroxyzine and its main metabolite cetirizine in healthy volunteers
Definitive PK study establishing hydroxyzine half-life of ~20 hours in adults, rapid conversion to cetirizine metabolite, and demonstrating that cetirizine accounts for ~45% of the oral dose.
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A comparison of hydroxyzine and cognitive behavioral therapy for the treatment of generalized anxiety disorder
Cochrane review finding hydroxyzine effective for short-term GAD treatment with NNT of 4.8, though limited evidence on long-term efficacy versus other treatments.
3 published studies referenced in the app, each with a plain-language summary.