People commonly conclude their antihistamine has stopped working and switch brands repeatedly. True pharmacological tolerance to second-generation antihistamines is not well established, and there are several more likely explanations worth ruling out first.
1. The Pollen Load Has Changed
A dose that controlled symptoms in April may be overwhelmed in June. Tree, grass and weed seasons overlap and peak at different times, and warm dry conditions with light winds keep far more pollen airborne.
The Met Office has been direct that there is no data supporting the claim that a given year's pollen is objectively "worse" — but seasons genuinely start earlier and stronger after warm spells, which changes the load your treatment is handling.
What to do: add a treatment rather than swap one. A steroid nasal spray alongside the tablet is the standard next step.
2. You Started Too Late
Antihistamines work considerably better preventively. Standard advice is to start two to four weeks before your symptoms usually begin, because it is easier to stop histamine release causing symptoms than to suppress an established response.
What to do: nothing this season, but diarise it for next year. Knowing which pollen affects you tells you when to start.
3. You Are Newly Allergic to Something Else
Sensitisation can develop over time. Symptoms that used to run May to July and now run March to September suggest an additional allergen — or a perennial one such as house dust mite that was always there underneath.
What to do: if symptoms are year-round, that is not hay fever alone and is worth investigating.
4. Your Main Symptom Is Congestion
Antihistamine tablets are relatively weak against nasal blockage. If your dominant complaint has shifted from sneezing and itching to a blocked nose, the tablet is not failing so much as being asked to do the thing it is worst at.
What to do: a steroid nasal spray is far more effective for congestion. It needs one to two weeks of consistent daily use to reach full effect.
5. Your Nasal Spray Technique Is Wrong
The most common reason a steroid spray "does not work". Aiming up the nose towards the bridge, sniffing hard, or using it only on bad days all defeat it.
What to do: head slightly forward, aim outward towards the ear on the same side, use the opposite hand to the nostril, breathe in gently. Daily, not as needed. If you taste it strongly, it went down your throat.
6. It Is Not Hay Fever
Non-allergic rhinitis, sinusitis, nasal polyps and medication side effects all produce similar symptoms and do not respond to antihistamines. Unilateral symptoms or blood-stained discharge need assessment rather than another product.
Switching Antihistamine — When It Is Reasonable
Switching is a legitimate step, and NHS advice acknowledges that if one antihistamine is not working well, trying another is worth doing. Fexofenadine is often tried when cetirizine has disappointed, and it is also the least sedating.
What is not productive is cycling through five brands of the same molecule. Own-brand cetirizine and branded cetirizine are the same drug; changing between them changes nothing but the price.
The Escalation That Usually Works
- Non-sedating antihistamine daily, started early
- Add a steroid nasal spray, used correctly and daily
- Add eye drops if eyes are the problem
- If still uncontrolled, see a pharmacist or GP — prescription combination sprays exist, and immunotherapy is an option for severe, poorly controlled allergy
Most people stop at step one and switch brands sideways instead of moving up.