Levocetirizine is an antihistamine used to treat seasonal and year-round allergies and chronic hives. Sold under the brand name Xyzal, it works by blocking histamine, the chemical your body releases during an allergic reaction that causes sneezing, itching, runny nose, and skin welts. It’s taken once daily in the evening and provides relief for a full 24 hours.
Approved Uses
Levocetirizine is approved for three specific conditions. The first is seasonal allergic rhinitis, the type of allergy triggered by pollen during certain times of year. The second is perennial allergic rhinitis, which involves year-round symptoms caused by triggers like dust mites, pet dander, or mold. The third is chronic idiopathic urticaria, a condition where hives appear repeatedly for six weeks or more without a clear cause.
For allergies, it’s approved in adults and children 6 months and older. For chronic hives, the same age range applies. It’s available over the counter in the United States, so you don’t need a prescription for most situations.
How It Differs From Cetirizine
Levocetirizine is the active half of cetirizine (Zyrtec). Cetirizine is made up of two mirror-image molecules, and levocetirizine is the one that actually binds to histamine receptors and does the work. This means 2.5 mg of levocetirizine produces roughly the same antihistamine effect as 5 mg of cetirizine. Research shows levocetirizine has about twice the binding affinity for histamine receptors compared to cetirizine as a whole.
If you’re wondering whether switching from cetirizine to levocetirizine will reduce drowsiness, the answer is probably not. A randomized, double-blind trial found no significant difference in sedation between the two drugs when measured on standardized sleepiness scales. If cetirizine makes you drowsy, levocetirizine is likely to do the same.
How Quickly It Works
Levocetirizine absorbs fast. It reaches peak levels in your blood within about 45 minutes to an hour after you take it on an empty stomach. Eating a high-fat meal delays that peak to around 2 hours, though the total amount absorbed stays the same.
In terms of actual symptom relief, the strongest effects kick in within 3 to 6 hours and last at least 24 hours. In children aged 6 to 11, a single dose showed significant antihistamine activity starting at 1 hour and lasting up to 28 hours. This long duration is why once-daily dosing is enough.
How Well It Works for Chronic Hives
For people dealing with persistent hives, levocetirizine has strong clinical evidence behind it. In a 6-week study of patients with moderate to severe chronic hives, 5 mg daily was significantly more effective than a placebo at reducing overall symptoms. Two separate 4-week trials found it significantly reduced both the severity and duration of itching compared to placebo. In one of those studies, it also outperformed desloratadine (Clarinex) on itch severity and duration, though the two drugs were similar when it came to reducing the number and size of welts.
Standard Dosing by Age
The recommended dose depends on age:
- Adults and children 12 and older: 5 mg once daily in the evening, taken as a tablet or liquid.
- Children 6 to 11: 2.5 mg (half a tablet) once daily in the evening.
- Children 2 to 5: 2.5 mL of oral solution once daily in the evening.
- Children 6 months to 2 years: 1.25 mg (2.5 mL of solution) once daily in the evening, with possible adjustments by a doctor.
Evening dosing is specifically recommended because any drowsiness will overlap with sleep rather than your waking hours.
Kidney Function Matters
Your kidneys handle most of the work clearing levocetirizine from your body. If your kidneys don’t function well, the drug builds up and side effects become more likely. People with mild kidney impairment should take a reduced dose, and those with moderate or severe impairment need to take it less frequently, sometimes only twice a week. People with end-stage kidney disease or those on dialysis should not take levocetirizine at all.
Side Effects and What to Watch For
The most common side effect is drowsiness. This is a “second-generation” antihistamine, meaning it causes far less sedation than older drugs like diphenhydramine (Benadryl), but it can still make some people sleepy. Other possible effects include dry mouth, fatigue, and headache.
Alcohol amplifies the sedating effects. Combining the two can impair your judgment, reaction time, and coordination more than either one alone. If you take levocetirizine, be cautious about drinking, especially before driving or doing anything that requires focus. The same applies to other sedating medications, including sleep aids and certain pain relievers.
Pregnancy and Breastfeeding
Levocetirizine carries a Category B pregnancy rating, meaning animal studies have not shown harm to a fetus, but no well-controlled human studies exist. It’s generally considered one of the safer antihistamine options during pregnancy, though it should only be used when the benefit clearly justifies it.
For breastfeeding, the picture is less favorable. Cetirizine (the parent compound) is excreted in human breast milk, and levocetirizine is expected to be as well. The FDA labeling specifically recommends against using it while nursing.