Can I overdose on 100 mg of vistaril (hydroxyzine)?

Max 400mg/day in adu. Although max dose of vistaril (hydroxyzine) is 400mg/day in adults, every one is different. Some common side effects are drowsiness, fatigue headache constipation. Report any irregular/fast heart beat, difficulty urinating, slurred speech or tremor to your doctor as soon as possible. Vistaril (hydroxyzine) starts it action in 15-60 mins after a dose / keeps working for~4-6hrs then out of the system 14-25 hrs. Drink lots water.