Cetirizine hydrochloride is an over-the-counter antihistamine used to relieve symptoms of hay fever, year-round allergies, and hives. It works within 20 to 60 minutes of taking a dose, and a single tablet provides relief for at least 24 hours.
Allergy Symptoms It Treats
Cetirizine was originally approved as a prescription medication in 1995 and switched to over-the-counter status in 2007. It’s approved to temporarily relieve these symptoms caused by hay fever or other upper respiratory allergies:
- Runny nose
- Sneezing
- Itchy, watery eyes
- Itching of the nose or throat
These symptoms can come from seasonal allergies (triggered by pollen at certain times of year) or perennial allergies (triggered year-round by things like dust mites, pet dander, or mold). Cetirizine is approved for both.
Hives and Chronic Urticaria
Beyond nasal and eye symptoms, cetirizine is approved to relieve itching caused by hives in adults and children ages 6 and older. This makes it one of the few antihistamines with a specific indication for skin-related allergic reactions, not just respiratory ones.
For chronic hives that last six weeks or longer, international treatment guidelines recommend second-generation antihistamines like cetirizine as the first-line treatment. If the standard dose doesn’t provide enough relief after about seven days, guidelines suggest the dose can be increased up to four times the standard amount under medical supervision. Cetirizine is one of the drugs with established safety data at these higher doses. Studies in both adults and children have confirmed its long-term safety for managing chronic hives.
How Cetirizine Works
When your body encounters an allergen, immune cells release histamine. Histamine binds to receptors on cells throughout your body, triggering the cascade of symptoms you recognize as an allergic reaction: swelling in your nasal passages, fluid leaking from blood vessels into tissues, itching, and sneezing.
Cetirizine blocks these histamine receptors before the chemical can activate them. It targets receptors on smooth muscle cells in your airways, blood vessel walls, immune cells, and the digestive tract. By preventing histamine from docking at these sites, cetirizine reduces swelling, stops fluid from leaking out of capillaries into surrounding tissue, and calms the itch signals that make allergies so miserable. It also has anti-inflammatory properties, reducing the movement of certain immune cells into inflamed tissue during an allergic reaction.
Why It Causes Less Drowsiness
Cetirizine is a second-generation antihistamine, which means it was designed to work primarily outside the brain. Older antihistamines like diphenhydramine (Benadryl) cross freely into the brain, where they block histamine receptors involved in keeping you awake and alert. Cetirizine doesn’t cross that barrier to nearly the same extent, so it produces significantly less sedation.
That said, drowsiness is still the most commonly reported side effect, along with dry mouth. Both are dose-dependent, meaning they’re more likely at higher doses. A meta-analysis of 13 clinical trials found that in well-designed studies, the drowsiness rate with cetirizine 10 mg daily was not statistically different from placebo. In practical terms, most people taking a standard dose won’t notice meaningful sedation, but some individuals are more sensitive than others.
How Quickly It Works
Cetirizine starts relieving symptoms within 20 to 60 minutes of taking it, which makes it one of the faster-acting antihistamines available. Its effects last at least 24 hours, so a single daily dose is typically all you need. It’s available as tablets, chewable tablets, liquid, and orally dissolving tablets.
Alcohol and Other Interactions
Alcohol is the most relevant interaction for everyday use. Because cetirizine can cause mild drowsiness on its own, combining it with alcohol amplifies that effect. The same applies to other substances that slow your central nervous system: sleep aids, anti-anxiety medications, muscle relaxants, and opioid pain medications. If you take any of these, the sedation from cetirizine becomes more noticeable and potentially problematic for driving or tasks that require alertness.
People with reduced kidney or liver function should be aware that cetirizine is cleared from the body more slowly when these organs aren’t working at full capacity. A lower dose may be appropriate in those situations.
How It Compares to Similar Medications
Cetirizine belongs to the same class as loratadine (Claritin) and fexofenadine (Allegra). All three are second-generation antihistamines with similar overall effectiveness for allergy relief. The practical differences come down to side effect profiles and individual response. Cetirizine tends to be slightly more likely to cause drowsiness than loratadine or fexofenadine, but some people find it provides stronger or faster relief. If one doesn’t work well for you, switching to another in the same class is a reasonable next step.
Cetirizine is also the parent compound of levocetirizine (Xyzal), which contains only the more active half of the cetirizine molecule. Levocetirizine works in essentially the same way at a lower milligram dose.