Zyrtec (cetirizine) typically starts working within 20 to 60 minutes after taking a dose, with peak blood concentration reached around 1 hour
. Its effects generally last about 24 hours, which is why it is usually taken once daily
. The elimination half-life of Zyrtec is approximately 8 to 9 hours, meaning it takes about 2 days (roughly 49.5 hours) for the medication to be fully cleared from the system after stopping it
. However, the symptomatic relief from a single dose lasts about a day, so daily dosing maintains effective allergy control
. In summary:
- Onset of action: 20–60 minutes
- Duration of effect: ~24 hours
- Half-life: 8–9 hours
- Time to clear from system: ~2 days after last dose
This makes Zyrtec suitable for once-daily dosing to provide continuous allergy symptom relief
