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Cetirizine is the most commonly used over-the-counter antihistamine in Germany. It helps with hay fever, allergic rhinitis, hives and allergic conjunctivitis — and takes effect after just 30 minutes.
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Cetirizine is available over the counter. This article is for information. If you are unsure about dosage or interactions, ask your doctor or pharmacist.
Cetirizine is one of the best-selling antihistamines worldwide – and for good reason. It works quickly, lasts 24 hours, and has been in use for over 30 years. What many people do not know: unlike most other antihistamines, cetirizine is excreted almost unchanged via the kidneys – which has important consequences for dosing in renal impairment.
| Property | Details |
|---|---|
| Active substance | Cetirizine dihydrochloride |
| ATC code | R06AE07 |
| Drug class | H1 antihistamine, 2nd generation |
| Available forms | Film-coated tablets (10 mg), drops, oral solution |
| Onset of action | 30–90 minutes |
| Duration of effect | Up to 24 hours |
| Half-life | Approx. 10 hours |
| Elimination | Predominantly renal (kidney) – unchanged! |
| Prescription status | No (over the counter from age 2) |
| Standard dose | 10 mg 1× daily (adults & children from 12 yrs) |
In an allergic reaction, the immune system wrongly recognises a harmless substance – pollen or house-dust mites, for example – as a threat. In response, mast cells and basophil granulocytes release the signalling molecule histamine. Histamine binds to H1 receptors in various tissues and triggers the familiar allergy symptoms: itching, swelling, sneezing, watery and reddened eyes, and a runny nose.
Cetirizine selectively blocks these H1 receptors – it occupies the receptor before histamine can dock. Histamine is still present in the blood but no longer finds a free receptor and cannot exert its effect. The allergy symptoms are thereby reliably suppressed.
The distinction between 1st and 2nd generation is highly relevant for patients. 1st-generation antihistamines – for example dimetindene (Fenistil) or diphenhydramine – pass the blood–brain barrier easily and are therefore strongly sedating. They make you extremely drowsy, which was even used therapeutically in the past (e.g. as a sleep aid). As an allergy treatment, however, they are unsuitable for anyone who has to stay functional during the day.
Cetirizine belongs to the 2nd generation: it is structured so that it crosses the blood–brain barrier much less well. The sedating effect is therefore considerably lower – but not zero. Around 10% of users report noticeable drowsiness. This is because the blood–brain barrier is permeable to different degrees in different people. Anyone who becomes drowsy on cetirizine is not an outlier – but belongs to the pharmacologically explained minority who benefit from a switch to loratadine or desloratadine.
Cetirizine is approved for the classic allergic conditions – but one advantage stands out in particular: as the only oral antihistamine in this comparison, cetirizine is also approved for allergic conjunctivitis (inflammation of the conjunctiva). Loratadine, for example, does not have this approval. So anyone who, alongside respiratory symptoms, also has pronounced eye symptoms is often better served by cetirizine.
| Indication | Approval |
|---|---|
| Seasonal allergic rhinitis (hay fever) | Yes |
| Perennial allergic rhinitis (house-dust mite) | Yes |
| Allergic conjunctivitis (eye symptoms) | Yes – advantage over loratadine! |
| Chronic spontaneous urticaria (hives) | Yes |
| Allergic skin reactions / itching | Yes |
| Atopic dermatitis (supportive) | Off-label, but frequently used |
The use in chronic urticaria deserves particular mention. In this condition, characterised by spontaneously appearing weals and intense itching, cetirizine has shown a stronger effect on skin symptoms than loratadine in studies. So anyone who suffers above all from skin reactions benefits more from cetirizine than from its comparator.
Cetirizine is taken by adults and children from 12 years of age at a standard dose of 10 mg once daily. The most important practical tip: if drowsiness is a problem, move the intake to the evening. That way you sleep through the sedating phase and are symptom-free during the day. This completely solves the drowsiness problem for many patients – without switching to a different product.
| Age group | Dosage | Note |
|---|---|---|
| Adults & children from 12 yrs | 10 mg 1× daily | In the evening if drowsy! |
| Children 6–12 years | 5 mg 2× daily OR 10 mg 1× | Depending on the product |
| Children 2–6 years | 2.5 mg 2× daily (= 5 mg/day) | Prefer drops/oral solution |
| Renal impairment (GFR < 30) | 5 mg 1× daily | Dose reduction! (renal elimination) |
| Hepatic impairment | No adjustment needed | Cetirizine is barely metabolised in the liver |
Drowsiness is by far the most common complaint on cetirizine and the main reason patients switch or stop the product. Yet the problem is easily managed – if you know the cause and the solution.
Cetirizine crosses the blood–brain barrier to a small extent – but not not at all. The brain also has H1 receptors, which play an important role in wakefulness and attention. Histamine in the brain acts as a "wakefulness promoter" – when cetirizine blocks these central H1 receptors, wakefulness decreases. In around 10% of users this effect is noticeable enough to impair everyday life. This varies a great deal from person to person: some fall asleep immediately on cetirizine, others notice nothing at all.
The simplest trick: take cetirizine in the evening. The maximum effective concentration is reached after 1–2 hours, but the substance lasts 24 hours. Anyone who takes the tablet shortly before sleep literally sleeps through the sedating phase and benefits during the day from the allergy protection without noticeable drowsiness. This completely solves the problem for the majority of those affected.
Anyone who is too drowsy during the day despite evening intake should switch to loratadine or desloratadine – both cause drowsiness at placebo level. More on this in chapters 6 and 7.
| Side effect | Frequency | Note |
|---|---|---|
| Drowsiness / sleepiness | Approx. 10% | The main problem! Evening intake helps |
| Headaches | Common | Usually temporary |
| Dry mouth | Occasional | Drink plenty of water |
| Nausea / gastrointestinal | Occasional | Taking it with food can help |
| Dizziness | Occasional | Especially in combination with alcohol |
| Tachycardia (palpitations) | Rare | See a doctor if you have palpitations! |
A note on driving: cetirizine can impair reaction time. Anyone who feels drowsiness or grogginess after taking it should not drive a vehicle or operate machinery. This applies especially in combination with alcohol. Anyone who depends on driving for work should prefer loratadine or desloratadine – neither has restrictions on fitness to drive.
"Which is better – cetirizine or loratadine?" is one of the most frequently asked questions in self-medication. The honest answer: it depends on the situation. Both belong to the 2nd generation of antihistamines, are equally inexpensive, and work for 24 hours. The differences are in the detail – but these details can be decisive in everyday life.
The most important difference is pharmacological: loratadine is a so-called prodrug – it is not active itself but is first converted in the liver into the active substance desloratadine. This explains several peculiarities at once: loratadine works more slowly (60–180 minutes instead of 30–90 with cetirizine), has more potential interactions via the liver enzyme CYP3A4, and needs a dose adjustment in severe hepatic impairment – whereas cetirizine can be used without problems in liver disease, because it is excreted via the kidneys.
| Property | Cetirizine | Loratadine |
|---|---|---|
| Onset of action | 30–90 minutes (faster!) | 60–180 minutes (prodrug!) |
| Duration of effect | 24 hours | 24 hours |
| Drowsiness | Approx. 10% (noticeable!) | Approx. 1% (barely noticeable) |
| Eye symptoms | Yes (approved!) | No (no approval) |
| Hives / skin symptoms | Yes – stronger on skin symptoms | Yes |
| Elimination | Renal (kidney – unchanged) | Hepatic (liver – prodrug) |
| Dose adjustment kidney | Yes! (at GFR < 30) | No |
| Dose adjustment liver | No | Yes! (in severe hepatic impairment) |
| CYP interactions | Barely any | Yes (CYP3A4/2D6) |
| Pregnancy | Possible (data: 1,300+) | Preferred! (data: 3,000+) |
| Driving / work | Possible with limits (drowsiness!) | Unrestricted |
| Cost | Very cheap (~€2–5/20 tabs) | Very cheap (~€2–5/20 tabs) |
