Allergex contains chlorphenamine — 4 mg tablets or 2 mg per 5 ml syrup — a sedating antihistamine. It relieves hay fever, allergic rhinitis, hives, itching and allergic reactions. It works well but causes marked drowsiness, so it should not be taken before driving.
What is Allergex?
Allergex contains chlorphenamine maleate, also spelled chlorpheniramine — 4 mg in the tablet and 2 mg per 5 ml in the syrup. It is a Schedule 2 medicine.
Check which Allergex you have. The range includes more than one product: alongside the chlorphenamine tablets and syrup there is Allergex Mepyramine cream, which contains a different antihistamine for topical use, and non-drowsy versions containing a second-generation antihistamine instead. They are not interchangeable, and the drowsiness caution applies specifically to the chlorphenamine forms.
An allergic reaction releases histamine from mast cells, and histamine acting on H1 receptors produces sneezing, a runny itchy nose, watery eyes, and in the skin, weals and itching. Chlorphenamine blocks those receptors.
It does that job well. What distinguishes it from a modern antihistamine is not effectiveness but where else it goes. Chlorphenamine crosses readily into the brain, where the same H1 receptors govern wakefulness, and blocking them there causes pronounced drowsiness. It also has antimuscarinic effects — dry mouth, blurred vision, urinary hesitancy.
Newer antihistamines such as the cetirizine in Zelary or loratadine were designed to cross far less, giving allergy control without sedation.
So chlorphenamine has become the second choice for daytime allergy — but it has not been superseded. Its sedation is sometimes exactly what is wanted, and it acts faster than the newer agents.
What is Allergex commonly used for?
- Hay fever and allergic rhinitis — sneezing, runny nose, itchy eyes and throat.
- Hives (urticaria) and allergic skin rashes.
- Itching from insect bites, chickenpox and eczema, particularly at night.
- Allergic reactions, including as part of the immediate management of more significant reactions in medical settings.
- Allergic conjunctivitis.
- Night-time symptom relief, where the sedation helps sleep.
Chlorphenamine is also present in many combination cold and flu remedies, where it dries a runny nose and contributes drowsiness to night-time formulations. That is the main way people take it without realising — and then take Allergex on top.
It does not treat a cold. Cold symptoms are viral, not histamine-driven. It may dry a runny nose somewhat, but it does not shorten the illness.
It does not treat asthma, and is not a substitute for an inhaler.
How Allergex fits into this medicine category
| Group | Examples | Note |
|---|---|---|
| First-generation antihistamines | Chlorphenamine (Allergex, Rhineton), promethazine | Effective and fast; markedly sedating |
| Second-generation antihistamines | Cetirizine (Austell Cetirizine, Zelary), loratadine | Once daily; little drowsiness |
| Steroid nasal sprays | Fluticasone, mometasone | Best for nasal congestion |
| Decongestants | Pseudoephedrine, oxymetazoline | Short-term congestion relief only |
| Combination cold and flu products | Various | Frequently contain an antihistamine already |
For daytime allergy, a second-generation antihistamine is generally the better choice. See the allergy, cold and flu medicines hub.
What to check before using Allergex
Do not drive or operate machinery after taking the chlorphenamine forms. This is the central caution. It impairs reaction time and judgement, and the impairment can persist into the following morning after an evening dose. People routinely underestimate this because it is a familiar over-the-counter medicine.
Do not drink alcohol with it — the sedation compounds substantially.
Check other products for an antihistamine. Cold and flu remedies, night-time preparations and allergy combinations often contain one already.
Speak to a pharmacist or doctor if:
- You have glaucoma, particularly narrow-angle.
- You have an enlarged prostate or difficulty passing urine.
- You have epilepsy.
- You have liver or kidney disease.
- You have asthma, COPD or bronchitis — chlorphenamine thickens secretions, making the chest harder to clear.
- You are pregnant or breastfeeding.
- You are older. First-generation antihistamines are associated with confusion, falls and urinary retention in older adults, and a non-sedating alternative is generally preferred.
- The medicine is for a child, particularly under 2, where it should not be used without medical advice.
- You take other sedating medicines, an antidepressant, or another antimuscarinic medicine.
- You are due allergy testing — antihistamines suppress skin prick tests and must be stopped days beforehand.
Follow the pack instructions. This page does not set doses.
Possible cautions and when to ask a pharmacist or doctor
Drowsiness is expected, not a surprise. Plan around it: take it in the evening where possible, and do not drive.
Do not use it as a sleeping aid. Sedating antihistamines are sometimes taken for insomnia, but tolerance to the sedation develops within days, and persistent insomnia needs its actual cause addressed.
Dry mouth, blurred vision, constipation and difficulty passing urine are common antimuscarinic effects.
In older adults, consider a non-sedating alternative. Confusion, falls and urinary retention are meaningfully more likely with this class, and cetirizine or loratadine gives the same allergy control without them. Worth raising with a pharmacist for an older relative.
Paradoxical excitement — restlessness or agitation instead of drowsiness — occurs in some children.
If allergy symptoms persist beyond a few weeks, get properly assessed rather than continuing indefinitely. Nasal congestion in particular responds much better to a steroid nasal spray.
Seek urgent medical attention for swelling of the face, lips, tongue or throat, difficulty breathing or swallowing, wheezing, or faintness with a widespread rash — hives with any mouth or throat swelling is an emergency. Also seek attention for eye pain with blurred vision or halos, or inability to pass urine.
Related medicine guides
Frequently asked questions
What is Allergex used for? Hay fever and allergic rhinitis, hives, itching and allergic reactions. The tablets and syrup contain chlorphenamine, a sedating antihistamine.
Will it make me drowsy? Yes, markedly. Do not drive after taking it, and the effect can persist into the next morning.
Is Allergex the same as Allergex Non-Drowsy? No. The non-drowsy versions contain a second-generation antihistamine instead. Check which you have.
What about Allergex Mepyramine cream? That is a different product — a topical antihistamine cream, not the chlorphenamine tablets.
Can I give it to my child? Ask a pharmacist. It should not be used in children under 2 without medical advice, and it can cause restlessness rather than drowsiness in some children.
Can I use it to help me sleep? It is not intended for that. Tolerance to the sedation develops within days, and ongoing insomnia needs its cause addressed.