Zyrtec (cetirizine) typically begins to work within 20 minutes for about 50% of people, and within 1 hour for around 95% of users, with peak blood concentrations reached at about 1 hour after taking it
. Clinical studies confirm that significant antihistamine effects can be noticed within 1 to 2 hours of administration
. The effects of a single dose of Zyrtec usually last for at least 24 hours, making once-daily dosing effective for most people
. Some users and allergists note that full symptom relief may improve further after several days of consistent use, as the medication builds up and inflammation subsides
. In summary:
- Onset of action: 20 minutes to 1 hour for most people
- Peak effect: around 1 hour
- Duration: about 24 hours
- Full effect may improve with daily use over several days
This rapid onset and long duration make Zyrtec a popular choice for quick and sustained allergy symptom relief
