How long does hydroxyzine (an antihistamine) take to start working?

How Long Does Hydroxyzine Take to Start Working?

Hydroxyzine typically begins working within 15 to 30 minutes after oral administration. 1

Pharmacokinetics and Onset of Action

• Hydroxyzine is rapidly absorbed from the gastrointestinal tract with clinical effects usually noted within 15 to 30 minutes after oral administration. 1
• The medication reaches peak plasma concentrations approximately 2-3 hours after administration. 2
• Hydroxyzine has a relatively long elimination half-life of about 20 hours in adults, which is shorter in children but prolonged in patients with liver disease. 2

Clinical Effects Timeline

• Initial effects begin within the first 30 minutes after ingestion. 1
• The sedative properties of hydroxyzine appear quickly and are most pronounced during the first few hours after administration. 3
• In studies examining hydroxyzine's effects on anxiety, a significant decrease in anxiety scores was observed by the end of the first week of treatment. 3

Factors Affecting Onset of Action

• The time of day when hydroxyzine is administered may affect its sedative properties:
  • Evening doses typically cause expected sedation. 4
  • Morning doses may actually produce more pronounced impairment in cognitive function compared to evening doses. 4
• Unlike some medications that require multiple doses to achieve therapeutic effect, hydroxyzine demonstrates effectiveness after the first dose. 3, 5

Common Side Effects Related to Onset

• Sleepiness is the most common side effect (28% vs 14% with placebo), typically appearing during the first week of treatment and progressively diminishing with continued use. 3
• Other early side effects may include dry mouth (14%), weight gain (12%), and impaired concentration (9%). 3
• Hydroxyzine significantly prolongs both simple and choice reaction times within 90 minutes after administration, which may affect performance of critical tasks. 6

Clinical Considerations

• Due to its rapid onset of action, hydroxyzine may be particularly useful when prompt relief of symptoms is needed. 1
• The sedative effects do not appear to develop tolerance over time, meaning the same dose continues to produce similar effects with ongoing use. 6
• For patients who need to perform tasks requiring alertness, the timing of hydroxyzine administration should be carefully considered due to its relatively quick onset of sedative effects. 6