Cetirizine
ZyrtecPubChem CID 2678 · 3D model
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Blocks histamine from docking onto its receptors outside the brain, stopping the sneezing, itching, and swelling of an allergic reaction before it can start.
How it works
Cetirizine works by getting in histamine's way. Histamine is the chemical your immune system releases when it overreacts to something like pollen or dust — it's what makes blood vessels leak and swell, nerves itch, and your nose run. Cetirizine sits on the docking sites (receptors) that histamine would normally attach to, mostly on cells outside the brain, so histamine can't trigger those symptoms in the first place. Because very little of the drug crosses into the brain, it causes much less drowsiness than older allergy pills like diphenhydramine. One dose starts working within about an hour and keeps working for a full day, which is why it's taken just once daily.
What it’s used for
Used to relieve seasonal and year-round allergy symptoms — sneezing, runny nose, itchy/watery eyes, and itchy nose or throat — triggered by things like pollen, dust mites, pet dander, and mold. Also used to treat chronic hives (chronic idiopathic urticaria) of unknown cause, cutting down on itching and the number and size of hives.
- Mechanism
- Second-generation H1 histamine receptor antagonist
- Drug class
- Small molecule
- Therapeutic area
- Allergy / Immunology