Taking two Xyzal tablets (10 mg total) in 24 hours is unlikely to cause serious harm, but it roughly doubles your chance of feeling drowsy compared to the standard dose. The recommended dose is one 5 mg tablet per day, and the label specifically says not to exceed that amount. If you’ve already taken a double dose, here’s what to expect.
The Most Likely Side Effect Is Drowsiness
The biggest difference between 5 mg and 10 mg of levocetirizine (Xyzal’s active ingredient) is sedation. In a clinical trial that directly compared the two doses, 25% of people taking 10 mg reported feeling sedated, compared to about 6% at the standard 5 mg dose. That’s a meaningful jump. The drowsiness was the only side effect that clearly increased at the higher dose.
Other side effects reported at 10 mg included dizziness, fatigue, constipation, and sleep disturbance, but these were less common and couldn’t be definitively linked to the higher dose. No serious adverse events occurred in the study. FDA clinical trials also noted that 10 mg “causes more somnolence than the other two doses” (2.5 mg and 5 mg), but dropout rates at 10 mg were actually similar to or lower than at lower doses, suggesting most people tolerated it without major problems.
What a Double Dose Feels Like
If you’re going to notice anything, it will likely hit within 3 to 6 hours of taking the second tablet. Xyzal reaches its peak effect in that window and stays active for about 24 hours. You might feel unusually sleepy, a bit foggy, or slightly dizzy. Some people won’t notice anything different at all.
The drug has a half-life of 7 to 8 hours, meaning your body clears it relatively quickly. After about two half-lives (roughly 14 to 16 hours), the extra dose will have largely worked its way out. Any drowsiness or grogginess should fade well before the next day.
When It Could Be More of a Problem
For most healthy adults, a one-time double dose is a minor issue. But there are situations where it matters more.
Xyzal is almost entirely cleared through the kidneys. If you have any degree of kidney disease, even a standard 5 mg dose can build up to levels far higher than intended. People with moderate kidney impairment are typically prescribed just 2.5 mg every other day. For someone in that situation, taking 10 mg could produce drug levels many times higher than normal, significantly increasing side effects. People with severe kidney problems or end-stage kidney disease should not take Xyzal at all.
Combining a double dose with alcohol, sleep medications, or other sedating drugs amplifies the drowsiness risk. If you’ve taken two Xyzal tablets, avoid driving or operating heavy equipment until you feel fully alert. This is especially true if you took the second dose during daytime hours rather than in the evening, when the label recommends taking it.
True Overdose Is a Different Story
Two tablets is not considered an overdose in a clinical sense, since 10 mg has been studied in controlled trials. A true overdose of antihistamines like levocetirizine, involving many times the recommended dose, can cause more concerning symptoms: significant drowsiness or the opposite (agitation and restlessness), rapid heart rate, confusion, and drops in blood pressure. These symptoms are associated with taking far more than a double dose and are not expected from two tablets.
What to Do Going Forward
Skip your next scheduled dose. Since Xyzal stays active in your body for a full 24 hours, you’re already covered. Wait until the following evening to take your regular 5 mg tablet and resume your normal schedule from there. There’s no benefit to doubling up: FDA trials found that 10 mg didn’t provide meaningfully better allergy relief than 5 mg, just more drowsiness. The 5 mg dose was chosen specifically because it hits the sweet spot of effectiveness with fewer side effects.
To avoid accidental double doses in the future, taking Xyzal at the same time each evening helps establish a routine. If you can’t remember whether you’ve already taken it, it’s generally better to skip that dose than to risk doubling up.