Allergy
Antihistamines
Relieve allergy symptoms; newer ones cause little drowsiness.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Antihistamines treat allergic conditions such as hay fever, hives (urticaria) and allergic reactions. They are widely available, including over the counter.
How it works
They block the H1 histamine receptor, reducing the itching, sneezing, runny nose and wheal-and-flare response that histamine drives during an allergic reaction.
In practice
In practice the key choice is sedating versus non-sedating. The newer non-sedating agents (e.g. cetirizine, loratadine, fexofenadine) are preferred for hay fever and urticaria because they work all day without impairing concentration or driving. Older sedating ones are best reserved for short-term or specific uses, and used cautiously in older people because of confusion and falls risk.
Examples
Practical use
How to take it & use it well
- Newer non-drowsy types such as cetirizine, loratadine and fexofenadine are usually taken once daily, often at the same time each day during the allergy season.
- For hay fever it can help to start before the pollen season and keep taking it regularly rather than only on bad days.
- Older sedating antihistamines are best taken in the evening, as they commonly cause drowsiness.
- If you miss a dose, take it when you remember unless the next one is due soon, then just continue as normal.
- Avoid alcohol with the sedating types, as it adds to drowsiness.
- Do not drive or use machinery if a sedating type makes you feel sleepy.
Common uses
- Allergic rhinitis (hay fever)
- Urticaria and itch
- Adjunct in allergic reactions
Monitoring
- Symptom relief and any drowsiness
- In the elderly, watch for confusion or falls with sedating agents
Weighing it up
Advantages & disadvantages
Advantages
- They ease itching, sneezing, a runny nose and watery eyes from hay fever and other allergies.
- The non-drowsy types let most people stay alert and carry on with daily activities.
- Many are available without prescription and are inexpensive.
- They can be taken regularly through an allergy season or used as needed for occasional symptoms.
- They also help with itchy skin and hives.
Disadvantages
- Older sedating types cause drowsiness and can affect concentration, driving and next-day alertness.
- They control allergy symptoms but do not cure the underlying allergy.
- Some people get a dry mouth, headache or mild stomach upset.
- They are less effective for a badly blocked nose than for sneezing and itching.
- Sedating types can be unsuitable for older adults, who are more sensitive to side effects such as confusion.
Key safety principles
What to watch for
- Older "sedating" antihistamines impair alertness and driving and can cause confusion in the elderly.
- Anticholinergic effects (dry mouth, urinary retention) with the older agents.
- They do not replace adrenaline in anaphylaxis.
Key interactions
What to avoid or check alongside
- Alcohol increases the drowsiness caused by sedating antihistamines.
- Other sedating medicines, including some painkillers, sleep aids and certain antidepressants, add to drowsiness when combined.
- Fexofenadine should not be taken at the same time as fruit juices like grapefruit, orange or apple, which can reduce its absorption.
- Indigestion remedies taken at the same time as fexofenadine can lower how much is absorbed.
- Combining several antihistamine products, including some cough and cold remedies, can lead to excessive sedation or side effects.
Patient & carer advice
- Choose a non-sedating type for daytime use
- Do not rely on antihistamines for a severe allergic reaction — use your adrenaline auto-injector and call for help
- Avoid alcohol with sedating types
Answers
Antihistamines: frequently asked questions
Which antihistamines are non-drowsy?
Cetirizine, loratadine and fexofenadine are the common non-drowsy options, though a small number of people still feel slightly sleepy on cetirizine.
Can I take antihistamines every day?
Yes, the non-drowsy types are often taken daily through the allergy season. If you need them long term, it is worth reviewing with a pharmacist or doctor.
Why does the older type make me sleepy?
Older antihistamines cross into the brain and have a sedating effect. That is why they are sometimes used at night, while newer ones are designed to avoid this.
Can children take antihistamines?
Some are suitable for children in age-appropriate forms, but always check the product label or ask a pharmacist, as not all types suit young children.
Will antihistamines help a blocked nose?
They work best for sneezing, itching and a runny nose. A blocked nose often responds better to a steroid nasal spray, which a pharmacist can advise on.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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