Antihistamine Q&As
Published by Bupa's health information team, September 2009.
Answers to questions about antihistamine
This section contains answers to common questions about this topic. Questions have been suggested by health professionals, website feedback and requests via email.
- What should I do if I take too much antihistamine?
- What is better for hay fever - antihistamine nasal sprays or tablets?
- Can you develop a tolerance to antihistamines (do they become less effective if you use them for a long time)?
What should I do if I take too much antihistamine?
You should tell your GP or pharmacist straight away if you take too much antihistamine. Go to your nearest accident and emergency department if you're feeling unwell.
Take the medicine packet(s) with you, so your doctor or pharmacist can see exactly what type of antihistamine you have taken.
Explanation
Antihistamines can have unpleasant or dangerous effects if you take too much. Symptoms of an overdose can be similar to the medicine's side-effects, but more severe. This may include making you feel sleepy, confused or dizzy, particularly with the older, sedating antihistamines. Alternatively, you may feel alert and jittery.
An overdose of antihistamines can cause more serious problems, such as a fast, irregular heart beat and breathing problems.
Remember that many different types of medicine can contain antihistamines, including cough medicines, travel sickness pills and sleep aids, as well as hay fever tablets and medicines for other allergies. It's easy to reach the maximum recommended dose of antihistamine without even realising it. Check the labels of all medicines you take and ask your pharmacist or GP for advice if you're unsure.
For certain conditions, doctors may advise you to take more antihistamine than stated on the packet as the recommended dose. You must only take more antihistamine under advice and supervision from your doctor - he or she will have experience in working out exactly how much you can take.
Sources
- Electronic medicines compendium. www.emc.medicines.org.uk, accessed 29 May 2009
- Urticaria. Clinical Knowledge Summaries. www.cks.library.nhs.uk, accessed 29 May 2009
What is better for hay fever - antihistamine nasal sprays or tablets?
There isn't enough evidence to say at the moment whether antihistamine nasal sprays or tablets are more effective for hay fever. What you take depends on your specific symptoms as well as your own personal preference.
Explanation
Antihistamine nasal sprays can help to reduce mild nasal symptoms, such as an itchy nose and sneezing, although they don't help with a blocked nose. They aren't as effective as nasal sprays that contain steroids, which also help with a blocked nose. Antihistamine tablets help with a wider range of hay fever symptoms - they can help with itchy eyes or roof of the mouth as well as nasal symptoms.
The advantage of antihistamine nasal sprays over antihistamine tablets is that they are faster-acting (usually you feel their effects within 15 minutes, compared to one to three hours with tablets). This means that you can just use them when you need quick relief from your symptoms. For tablets to be effective, you need to start taking them before your symptoms start, and you need to take them regularly.
Talk to your pharmacist or GP if you're unsure which treatment is best for you.
Sources
- National Prescribing Centre. Common questions about hay fever. MeReC Bulletin 2004; 14(5):17-20
Can you develop a tolerance to antihistamines (do they become less effective if you use them for a long time)?
No, you won't become tolerant to antihistamines if you use them for a long time.
Explanation
Some people think they have developed a tolerance to antihistamines after using them for a long time, because the drugs seem to be less effective.
However, studies show that their effects do not wear off even if you take them every day for three months.
If your antihistamine tablets no longer seem to be working, it may be because you aren't taking them at the best possible time to prevent a reaction. Antihistamine medicines are best taken regularly to prevent allergic symptoms. They also need to be taken well before symptoms develop, as it can take a couple of hours for them to work. If you have an allergic reaction in this time, your body would have already produced histamine and it will be too late for the antihistamine medicine to do its job.
You could also try a different brand of antihistamine if your medicine doesn't seem to be working, as people respond differently to different types of antihistamine. If your symptoms still aren't relieved, it may be because the types of symptom you are getting are particularly severe and can't be helped by antihistamines. You may need a different type of medicine.
Talk to your pharmacist or GP and he or she will recommend another treatment if necessary.
Sources
- del Cuvillo A, Mullol J, Bartra J, et al. Comparative pharmacology of the H1 antihistamines. J Investig Allergol Clin Immunol 2006; 16(Suppl 1):3-12
- Simons FER. Advances in H1 - antihistamines. New Engl J Med, 2004; 351(21):2203-17
- Allergic Rhinitis. Clinical Knowledge Summaries. www.cks.nhs.uk, accessed 29 May 2009
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This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
Publication date: September 2009
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