Cetirizine is a second-generation antihistamine used for hay fever, other allergies and urticaria. It blocks histamine at H1 receptors, reducing sneezing, runny nose, and itchy or watery eyes.
It is available over the counter throughout the UK, in supermarkets as well as pharmacies, and it is one of the cheapest effective medicines you can buy for anything.
Dose
- Adults and children 12 and over: 10mg once daily
- Children 6 to 11: usually 5mg twice daily, or as directed
- Under 6: follow the specific product's label and take advice from a pharmacist
It comes as tablets and as an oral solution, which is useful for children and anyone who dislikes tablets.
Speed of Onset
This is cetirizine's strongest suit. It typically starts working within 20 to 60 minutes, with peak effect around an hour. That makes it a good choice for symptoms that flare unpredictably, and a good choice if you have forgotten to take anything and are already outdoors and suffering.
For comparison, fexofenadine generally takes one to two hours to get going.
The Drowsiness Question
Cetirizine is classed as non-drowsy, and for most people it is. But it is the most sedating of the common second-generation antihistamines, and around one in ten to one in twenty users notice some drowsiness.
The MHRA advises caution with driving and operating machinery until you know how it affects you. If you take it and feel even slightly dulled, that is a reason to switch to fexofenadine or loratadine rather than to push through — driving while impaired by medication is an offence regardless of whether the medicine was bought over the counter.
Alcohol amplifies the effect. Combining the two is where most problems arise.
Other Side Effects
Uncommon, and usually mild: headache, dry mouth, fatigue, and occasional stomach discomfort. Serious effects are rare.
When to Start Taking It
Antihistamines work best preventively. Starting two to four weeks before your usual symptom onset is the standard advice, because it is easier to stop histamine release causing symptoms than to suppress symptoms already established.
That means knowing roughly which pollen affects you: tree pollen is late March to mid-May, grass pollen mid-May to July, and weed pollen from late June into September.
Cost
Cetirizine is the reference point for cheap in this category. Own-brand packs from supermarkets and pharmacies contain the same active ingredient at the same dose as branded versions such as Piriteze or Zirtek, at a fraction of the price. Larger packs are cheaper per tablet, and for a whole season that difference is meaningful.
There is no clinical reason to buy the branded version. This is the clearest example in the whole hay fever category of paying for a name.
Who Should Check First
- People with significant kidney impairment may need a reduced dose
- Pregnancy and breastfeeding — ask a pharmacist or GP; other options may be preferred
- Anyone taking sedating medicines, where the drowsiness effect can compound
If It Is Not Enough
An antihistamine alone often will not control moderate to severe hay fever. The usual next step is adding a steroid nasal spray, which is more effective for congestion than any tablet. Combining the two is standard practice rather than escalation, and if you are still struggling on both, that is the point to see a pharmacist or GP rather than doubling the dose.