The standard adult dose of cetirizine is one 10 mg tablet per day, taken once. That single daily dose is the maximum listed on over-the-counter packaging for adults and children 12 and older. Most people do not need more than this, and taking a second tablet won’t make the medication work significantly better for typical allergy symptoms.
Standard Doses by Age
Cetirizine is a once-daily antihistamine. Unlike some older allergy medications that wear off and need to be taken two or three times a day, cetirizine stays active in your body long enough that one dose covers a full 24 hours. Here’s what that looks like across age groups:
- Adults and children 12+: 10 mg once daily (one standard tablet)
- Children 6 to 11: 5 to 10 mg once daily, depending on the child’s response
- Children 2 to 5: 2.5 mg once daily, which can be increased to 5 mg per day
- Infants 6 to 23 months: 2.5 mg once daily
Some people start with 5 mg to see if it controls their symptoms before moving up to 10 mg. If 5 mg does the job, there’s no reason to take more.
When Doctors Prescribe Higher Doses
For chronic hives (urticaria) that don’t respond to the standard 10 mg dose, some doctors prescribe 20 mg per day. This is an off-label use, meaning it goes beyond what’s printed on the packaging but is still a recognized practice in allergy care. The UK’s National Institute for Health and Care Excellence has reviewed evidence on this higher dose specifically for stubborn hives.
In the studies NICE reviewed, 20 mg did not cause dramatically more side effects than 10 mg. Drowsiness rates were similar between the two doses in most trials. In one small study, two people felt drowsy on 20 mg but not on 10 mg, while one person actually felt drowsy on 10 mg but not on 20 mg. The point is that doubling the dose isn’t inherently dangerous for most healthy adults, but it’s something to do under medical guidance rather than on your own.
What Happens If You Take Too Much
If you accidentally took an extra tablet, the most likely outcome is drowsiness. Cetirizine is generally well tolerated, but higher doses amplify its sedating effects along with other side effects like dizziness, headache, and dry mouth.
Poison Control has documented cases that illustrate the typical outcome. A 75-year-old woman who accidentally took 30 mg (three tablets instead of one) became drowsy but experienced no serious effects. A 12-month-old who swallowed roughly 60 mg of liquid cetirizine also became sleepy and was monitored at home without needing emergency treatment.
That said, “not immediately dangerous” is different from “fine to do regularly.” Taking more than the recommended dose day after day increases your exposure to side effects and puts unnecessary strain on your kidneys and liver, which are responsible for clearing the drug from your body.
People Who Should Take Less
Not everyone should take the full 10 mg. The FDA-approved labeling recommends 5 mg once daily for people with reduced kidney function, those on dialysis, and anyone with liver problems. Your body clears cetirizine more slowly when these organs aren’t working at full capacity, so a standard dose lingers longer and acts more like a higher dose in practice.
Older adults often fall into this category even without a diagnosed kidney or liver condition, since organ function naturally declines with age. Starting at 5 mg is a reasonable approach for anyone over 65, especially those taking other medications.
Why One Tablet Feels Like It’s Not Enough
If your standard dose isn’t controlling your symptoms, the issue usually isn’t that you need more cetirizine. A few things could be going on. You might be dealing with non-allergic congestion, which antihistamines don’t address well. Your symptoms might benefit from adding a different type of medication, like a nasal corticosteroid spray, rather than doubling up on the same one. Or the timing of your dose might matter: taking cetirizine at night, for example, means peak levels align with early-morning allergy symptoms.
Switching to a different antihistamine is another option. Some people respond better to one than another, even though they all work through a similar mechanism. If 10 mg of cetirizine leaves you still sneezing, trying a different antihistamine is generally a better strategy than simply taking two cetirizine tablets.