Fast-Acting Relief: Zyrtec provides rapid allergy relief for most people, with effects often starting within 20 to 60 minutes. Not Instantaneous: While quick, Zyrtec is not 'immediate.' It takes time for the medication to be absorbed and reach peak concentration in your blood. Zyrtec, like all other antihistamines, may decrease the response to skin prick tests. Discontinue Zyrtec at least 72 hours before skin testing. Weigh up the risks versus benefits before using during pregnancy and breastfeeding. Zyrtec typically starts working within 20-60 minutes of taking your first dose. Peak effectiveness occurs within 1 hour and lasts up to 24 hours. Clinical studies show that 95% of patients experience symptom relief within the first hour of administration. Zyrtec typically starts to work within one hour for most people, providing rapid relief from allergy symptoms, although the full effect may take a bit longer. How quickly does Zyrtec work? depends on individual factors, but it’s known for its relatively fast-acting nature. Zyrtec usually starts working within about 20 to 60 minutes, and most people feel some relief within an hour. For some people the effects begin to show even sooner than that. Zyrtec typically takes about 20 to 60 minutes to start working and generally lasts about 24 hours. And most people can safely take it long term to help prevent allergy symptoms. Zyrtec (cetirizine) treats seasonal and year-round allergy symptoms—sneezing, runny nose, itchy eyes, and hives. Many people feel relief within an hour. Once-daily dosing covers about 24 hours for most adults. Less than Benadryl, but cetirizine still sedates some people—test on a workday before assuming you are immune. Zyrtec typically starts working within an hour, but timing and a few simple habits can help you get allergy relief faster. Zyrtec starts working within 20 minutes for about half of people, and within one hour for 95% of people. That makes it one of the faster over-the-counter allergy medications available. How long does it take for Zyrtec to work? Zyrtec typically begins to work within an hour after you take it, but how well it works and how long it lasts can vary depending on different factors.