Hay Fever Antihistamines Compared
Cetirizine, loratadine, fexofenadine and the rest do much the same job. What actually separates them is drowsiness, speed, and one thing none of them can do.
Part of the Complete Hay Fever Guide.
Key fact: The non-drowsy antihistamines are broadly equally effective for sneezing, itching and a runny nose. What separates them is how much they make you drowsy and how fast they act — not how strong they are. And none of them does much for a blocked nose.
What an antihistamine actually does
When pollen lands on the lining of the nose or the surface of the eye in someone sensitised to it, mast cells release histamine within minutes. Histamine acting on H1 receptors produces a very specific set of symptoms: sneezing, itching, watering eyes and a streaming nose. An antihistamine blocks those receptors, so it works well against exactly those four things.
That specificity is the whole point, and it explains the commonest disappointment with them. The blocked feeling in hay fever is not histamine. It is swelling of the nasal lining driven by a slower wave of inflammation involving different chemical messengers entirely, arriving hours after the exposure. Blocking histamine does almost nothing to it, which is why someone whose main complaint is a blocked nose can take an antihistamine faithfully for a fortnight and conclude that nothing works.
The two generations
Antihistamines split into two groups, and the split matters more than any brand difference within them.
First generation
Chlorphenamine and its relatives cross readily into the brain, where histamine is a wakefulness signal. They work, but they sedate — and the sedation is not confined to the hours you feel sleepy. They are short-acting, so they need taking several times a day.
Second generation
Cetirizine, loratadine, fexofenadine, levocetirizine and desloratadine were designed not to enter the brain in meaningful quantities. They last a full 24 hours, so they are taken once daily, and most people notice no sedation at all.
For daytime hay fever in an adult who has to function, a second-generation antihistamine such as fexofenadine or cetirizine is the sensible starting point. There is no clinical advantage to the older drugs that offsets the impairment they cause.
The options compared
| Medicine | Generation | Onset | Drowsiness | Worth knowing |
|---|---|---|---|---|
| Fexofenadine (also sold as Allevia 120mg) | Second | 1–2 hours | Lowest of any | The least sedating option available, including at higher doses. Absorption is reduced substantially by fruit juice, so it is taken with water. |
| Cetirizine | Second | Around 1 hour | Slight, in a minority | The fastest-acting of the non-drowsy group. A small proportion of people do feel mildly sleepy on it. |
| Levocetirizine (Xyzal) | Second | Around 1 hour | Slight, in a minority | The active half of cetirizine, given at half the dose. Same behaviour, no meaningful advantage for most people. |
| Loratadine | Second | 1–3 hours | Minimal | The one with the longest track record in pregnancy. Slower to take effect than cetirizine. |
| Desloratadine (Neoclarityn) | Second | 1–3 hours | Minimal | The active metabolite of loratadine. Useful mainly as an alternative if loratadine suits you but is not available. |
| Acrivastine (Benadryl Allergy Relief) | Second, short-acting | Around 30 minutes | Mild | Fast on and fast off, taken three times a day. Suits occasional, predictable exposure better than a whole season. |
| Chlorphenamine (Piriton) | First | Under 1 hour | Marked | Reliable and quick, but sedating enough to impair driving and next-day performance. Best reserved for night-time itching. |
Which of these are stocked, in which strengths and formulations, is set out on our allergies and hay fever medication page.
Drowsiness, driving and work
This is the part that deserves more attention than it usually gets. Sedating antihistamines measurably impair reaction time, vigilance and driving performance, and in formal testing the impairment has been shown to be comparable to being over the drink-drive limit. It is an offence to drive while impaired by a medicine, whether or not it was bought over the counter.
The morning after. Chlorphenamine taken at bedtime can still be impairing performance the following morning, which is precisely when people assume it has worn off. If you take a sedating antihistamine at night and drive early, you are the case this warning is about.
There is a second, less obvious cost. Sedating antihistamines suppress REM sleep, so the sleep they produce is not restorative. “It knocks me out” is a description of sedation, not of a good night. For someone whose hay fever is wrecking their sleep, treating the nose properly — so they can breathe through it — does far more for sleep quality than sedating them through the symptoms.
Why none of them unblock a nose
If your dominant symptom is congestion rather than sneezing, the antihistamine is the wrong lever. The most effective single treatment for nasal blockage in hay fever is a steroid nasal spray used every day through the season, because it acts on the inflammation that causes the swelling rather than on histamine.
The two are not alternatives. Used together they cover different symptoms, and for anyone with both a runny nose and a blocked one that combination is the standard approach rather than a last resort. The trade-offs between a spray and a tablet are set out in our guide to Avamys versus fexofenadine.
Decongestant sprays are a different thing entirely. Xylometazoline unblocks a nose within minutes by constricting blood vessels, and it is genuinely useful for a few days. Used beyond about a week it causes rebound congestion — a nose more blocked than it was to begin with, and dependent on the spray to open at all.
Choosing between them
| If this is your situation | Reasonable choice |
|---|---|
| You drive, operate machinery, study or need to concentrate | Fexofenadine, the least sedating of the group |
| You want the quickest effect from a non-drowsy option | Cetirizine or levocetirizine |
| You are pregnant or breastfeeding | Loratadine and cetirizine have the most reassuring data, but confirm with a clinician first |
| One antihistamine has not helped at all | Switching to a different one is reasonable — individual response varies more than the averages suggest |
| Your main problem is a blocked nose | Add a steroid nasal spray; changing antihistamine will not fix it |
| Itching wakes you at night | A sedating antihistamine at bedtime is a legitimate short-term option, but not a daytime plan |
| Your eyes are the worst part | Add antihistamine or mast-cell-stabiliser eye drops — they reach the eye surface in a way a tablet cannot |
Getting more out of the one you take
- Take it every day, not when symptoms appear. Antihistamines are considerably better at preventing a reaction than at reversing one that is underway. Taken daily through the season they work; taken reactively they disappoint.
- Start before your season does. The nasal lining becomes progressively more reactive with repeated exposure, so getting ahead of it takes less medicine than catching up.
- Do not take fexofenadine with fruit juice. Apple, orange and grapefruit juice reduce how much is absorbed, by enough to matter. Water only.
- Do not double up. Two antihistamines at once adds side effects without adding benefit. If one is not enough, add a different class — a spray or eye drops — rather than a second tablet.
- Give a switch a fair trial. A few days, taken consistently, before deciding it has not worked.
If you are doing all of that and still struggling, the problem is usually elsewhere: technique, timing, or something that is not hay fever. That is covered in hay fever treatment that is not working.
Frequently Asked Questions
Which antihistamine is strongest for hay fever?
None of the non-drowsy antihistamines is meaningfully stronger than the others for sneezing, itching and a runny nose. Comparative studies show broadly similar effectiveness. The differences worth choosing on are drowsiness, where fexofenadine is the lowest, and speed of onset, where cetirizine is the fastest. If one is not working for you, switching is reasonable, because individual response varies more than the averages do.
Do antihistamines work better if you take them before symptoms start?
Considerably better. Antihistamines block histamine receptors before histamine reaches them, so they are far more effective at preventing a reaction than at reversing one already under way. There is a second reason too: repeated pollen exposure makes the nasal lining progressively more reactive as a season goes on, so a nose kept calm from the outset needs less treatment than one being chased after the fact.
Why has my antihistamine stopped working?
Usually it has not. What has typically changed is that the pollen count has risen, or that congestion has become the dominant symptom and an antihistamine was never going to treat that. True loss of effect over time is uncommon with second-generation antihistamines. Before switching, check whether the problem is a blocked nose, in which case adding a steroid nasal spray is what is needed.
Can I take two different antihistamines together?
There is no benefit in taking two second-generation antihistamines together, and it adds side effects. If one is not controlling your symptoms, the productive move is to add a different type of treatment that targets a different mechanism, such as a steroid nasal spray for congestion or antihistamine eye drops for the eyes, rather than a second tablet.
Does it matter what time of day I take it?
For a once-daily antihistamine, consistency matters more than timing, but taking it in the evening means the peak blood level falls in the early morning, when pollen counts rise and symptoms are often worst. If you take a sedating antihistamine, taking it at night is standard, though it may still impair you the following morning.
References
- NHS. Hay fever. nhs.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Allergic rhinitis. cks.nice.org.uk
- British Society for Allergy & Clinical Immunology. BSACI guideline for the diagnosis and management of allergic and non-allergic rhinitis. bsaci.org
- Joint Formulary Committee. British National Formulary: antihistamines, allergen immunotherapy and allergic emergencies. bnf.nice.org.uk
- electronic Medicines Compendium. Summaries of Product Characteristics. medicines.org.uk
- Met Office. Pollen forecast and the UK pollen calendar. metoffice.gov.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Allergy medicines differ in how much drowsiness they cause and in who can take them, and decongestant nasal sprays are not for long-term use. If you have asthma, breathing symptoms that worsen alongside hay fever need review rather than more antihistamine. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.