How long does it take for the effects of hydroxyzine to wear off?

HYDROXYZINE: In healthy individual (i mean no liver, kidney or other metabolic diseases): onset of action- 15 to 30 minutes after intake; duration of action 4-6 hours- when you take recommended dose. If you are taking other medicines e.g. Barbiturates, central nervous system depressant medications, etc. The effect may be longer.

12 to 72 hrs: Drowsiness usually subsides in less than 12 hrs but the antihistamine activity may last around 72 hrs (some argues that it may last up to a week).