This Is How Long It Takes For Zyrtec To Start Working

Zyrtec is a brand name for cetirizine, an antihistamine that helps to relieve allergy symptoms such as itching, runny nose, sneezing, watery eyes, and itchy throat (via Generally speaking, antihistamines work to block histamine — a chemical produced by the body during an allergic reaction. 

The U.S. Food and Drug Administration approved the brand Zyrtec as a prescription drug in 2004. However, a 2020 study published in the journal Clinical and Molecular Allergy notes that the history of cetirizine, the main ingredient in Zyrtec, began over 30 years ago. It remains one of the most used drugs today, playing a leading role in the medical care of allergic diseases.

If you've been prescribed this medicine, you might wonder how long it takes to start working. Various factors can come into play to determine how quickly the medicine will work, including the type of formula you've been prescribed. For example, antihistamines like cetirizine come in several forms. According to the NHS, this includes tablets, syrups, liquids, eyedrops, creams, and nasal sprays. 

How long does Zyrtec take to work?

According to, Zyrtec generally takes 20 minutes to work in some people, while others may experience relief about one hour after administration. One hour is also when the drug reaches its peak concentration. Healthline reiterates this claim, stating that people who take antihistamines should feel relief in as little as one hour. As for the dosage, your doctor's prescription should normally advise on this. But as a guide, the NHS advises that adults can take one 10 mg tablet daily. For children ages 6 to 11, one 5 mg tablet twice daily will suffice; children 2 to 5 years get one 2.5 mg tablet twice per day.

It's also worth pointing out that various lifestyle factors might affect how Zyrtec will perform its work. Smoking, alcohol, and the use of illegal drugs might interact with the medication, according to Cleveland Clinic. It's therefore crucial to adhere to your doctor's prescription and adopt best practices when taking Zyrtec.

Common side effects and warnings

Generally speaking, cetirizine or Zyrtec can help manage allergic reactions for people of all ages. However, taking allergy medication daily can have side effects that vary and can impact individuals differently. For this reason, it's crucial to consult your doctor before taking Zyrtec. Medline Plus advises against self-medicating and to take the medicine exactly as directed. also warns that antihistamines like Zyrtec are known to cause drowsiness and can impair your thinking or reactions. Therefore, you'll have to be extra careful if you're driving or doing any activity that requires alertness and concentration. Healthline further reiterates this claim, advising against using heavy machinery at work or home until you've taken it for a while and you understand how your body reacts to it. Lastly, be aware that drug interactions might change how Zyrtec works, according to Mayo Clinic. So it helps to remind your doctor of the other medications you're taking.