Zyrtec (cetirizine) is taken once a day. A single 10 mg dose starts working within 20 to 60 minutes and suppresses allergy symptoms for a full 24 hours, so there’s no need to take it more than once daily.
Standard Dosing for Adults and Children
For adults and children 12 and older, the standard dose is one 10 mg tablet once a day. You can take it at any time, though most people choose the morning so it’s active throughout the day when they’re exposed to allergens.
For younger children, the doses are lower:
- Ages 6 to 11: 5 mg once daily (one 5 mg chewable tablet or one teaspoon of liquid)
- Ages 2 to 5: 2.5 mg once daily (half a teaspoon of liquid)
In both age groups, the recommendation is once a day in the morning. Studies in children ages 2 to 12 show that a single dose suppresses the allergic response within one hour and maintains that effect for a full 24 hours, just like in adults.
Morning vs. Evening Dosing
There’s no evidence that one time of day is more effective than another. Most people take Zyrtec in the morning simply because that’s when allergy symptoms tend to bother them. However, a small percentage of people feel drowsy on cetirizine. If you’re one of them, taking it in the evening lets the drowsiness overlap with sleep rather than your workday. The 24-hour duration means it’ll still be working when you wake up.
Dosing for Chronic Hives
Zyrtec is also used for chronic hives (urticaria), and the starting dose is the same: 10 mg once daily. What’s different is what happens when that dose isn’t enough. European allergy guidelines recommend that doctors may increase the dose of a non-sedating antihistamine up to four times the standard amount for stubborn chronic hives. Small clinical trials have found that 20 mg daily can improve hives and itching in people who don’t respond to the standard 10 mg. This is considered off-label use, meaning it goes beyond what’s printed on the box, and should only be done under a doctor’s direction.
Alcohol and Drowsiness
Cetirizine is a second-generation antihistamine, which means it causes far less drowsiness than older allergy medications like diphenhydramine (Benadryl). Still, it’s not completely free of sedating effects. Drinking alcohol while taking Zyrtec can amplify any drowsiness you experience. Because the drug stays active in your system for 24 hours, spacing out your dose and your drink doesn’t fully eliminate the overlap. If you’re driving or operating machinery, it’s safest to skip alcohol on days you take it.
What Happens When You Stop After Long-Term Use
If you’ve been taking Zyrtec daily for months or years, stopping abruptly can sometimes trigger intense itching that has nothing to do with your original allergy symptoms. The FDA issued a warning about this in 2023 after identifying 209 cases worldwide. The itching typically starts within one to two days of stopping the medication and can be severe enough to be debilitating.
Among reported cases where people noted how long they’d been taking the drug, 92% had used it for more than three months. The median duration of use before this withdrawal itching occurred was about 33 months. When people restarted cetirizine, the itching resolved in 90% of cases. Tapering off gradually after restarting worked for about 38% of those who tried it.
This doesn’t mean Zyrtec is unsafe for long-term use. The effect is considered rare relative to the millions of people who take it. But if you’ve been on it daily for several months and want to stop, tapering your dose down gradually rather than quitting cold turkey is a reasonable approach. Cutting tablets in half or alternating days for a week or two can ease the transition.
People Who May Need a Lower Dose
People with significant kidney problems may need a reduced dose because cetirizine is cleared through the kidneys. If kidney function is impaired, the drug stays in the body longer, which can increase the risk of drowsiness and other side effects. Older adults, who often have reduced kidney function even without a diagnosis, may also be more sensitive to the standard 10 mg dose and do better on 5 mg daily. Your pharmacist can help you figure out whether an adjustment makes sense based on your health history.