Zyrtec (cetirizine) is taken once a day, and that single dose lasts a full 24 hours. The standard adult dose is 10 mg, and the maximum recommended amount in a 24-hour period is 10 mg for most people. Taking a second dose the same day won’t make it work better and increases the risk of drowsiness.
Standard Dosing for Adults and Children
For adults and children 12 and older, the recommended dose is 5 to 10 mg once daily. Most people take the full 10 mg tablet. You can take it with or without food, and it doesn’t matter what time of day you choose, as long as you space your doses about 24 hours apart. If you’re someone who gets drowsy from it, taking it at bedtime is a common workaround.
For younger children, the doses are lower:
- 6 months to 23 months: 2.5 mg once daily (max 2.5 mg per day)
- 2 to 5 years: 2.5 mg once daily, which can be increased to 5 mg per day
- 6 to 11 years: 5 to 10 mg once daily (max 10 mg per day)
Children’s liquid formulations come in different concentrations, so always check the label before measuring a dose.
What If One Dose Isn’t Enough?
Some people find that a single 10 mg dose doesn’t fully control their symptoms, especially with chronic hives. In that situation, some doctors prescribe 20 mg per day (10 mg twice daily), though this is considered off-label, meaning it goes beyond what the standard packaging recommends. European allergy guidelines actually suggest that non-sedating antihistamines like cetirizine can be increased up to four times the standard dose when the usual amount isn’t effective for hives.
Small clinical studies have shown that 20 mg daily can improve itching and welts in people with stubborn chronic hives that didn’t respond to the standard 10 mg. However, this kind of dose increase should only happen under a doctor’s guidance, not on your own. Higher doses make drowsiness more likely, and there isn’t strong safety data beyond 20 mg per day.
What Happens If You Take Too Much
If you accidentally double up on a dose, the main symptom you’ll notice is drowsiness. Poison Control has documented cases where accidental extra doses caused sleepiness but nothing more serious in otherwise healthy people. A 75-year-old woman who accidentally took 30 mg (three tablets) became drowsy. A toddler who ingested about 60 mg of the liquid form also became very sleepy but recovered.
Doubling your dose once by mistake is not a medical emergency for most people, but it’s not something to make a habit of. If you realize you’ve taken an extra dose, skip the next scheduled one and resume your normal timing the following day.
Taking Zyrtec Every Day Long-Term
Many people take Zyrtec daily for months or years to manage seasonal or year-round allergies, and for most, this is well tolerated. Common side effects with regular use include fatigue, drowsiness, dry mouth, and sore throat.
There is one important thing to know about long-term use. In 2023, the FDA issued a warning about a rare but potentially severe side effect: intense itching that starts after you stop taking cetirizine. The FDA reviewed 209 reported cases, and in nearly all of them, the itching began within one to five days of stopping the medication. The median time people had been taking the drug before experiencing this withdrawal itching was about 33 months, though it happened in some people after just a few months. In roughly 92% of cases where usage duration was reported, the person had been taking it for more than three months.
The itching was severe enough in some cases to be disabling. Among people who tried restarting the medication, 90% found that the itching resolved. Tapering off gradually, rather than stopping all at once, resolved symptoms in about 38% of people who tried that approach. If you’ve been taking Zyrtec daily for a long time and want to stop, gradually reducing your dose over a week or two is a reasonable strategy to minimize this risk.
When to Start With a Lower Dose
Some people should start at 5 mg rather than 10 mg. If you have kidney or liver problems, the drug clears from your body more slowly, which means it stays at higher levels longer and side effects like drowsiness become more likely. Older adults may also benefit from starting at the lower dose for the same reason, since kidney function naturally declines with age. The 5 mg dose is still effective for many people, so starting low and seeing if it controls your symptoms is a perfectly valid approach regardless of your health status.