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Sedating antihistamines

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 2 minutes read

Antihistamine tablets are a group of medications that prevent the level of histamine from rising in the body and reduce the symptoms this can cause. Antihistamines can be used to treat a range of conditions, including allergic reactions, motion sickness, and insomnia. However, the term "antihistamines" most commonly refers to medications that are used to treat hay fever.

Antihistamines can be classified as sedating (drowsy) or non-sedating. With sedating antihistamines, care should be exercised when driving or operating heavy machinery, and alcohol should be avoided. Below, Healthwords pharmacists will go into more detail about the different antihistamines and their side effects.

Doctor’s advice

Who should take antihistamines

If you are suffering from hay fever or allergic-type symptoms such as an itchy nose, itchy rash or bite on the skin, or redness and minor swelling of the skin, then an antihistamine may help relieve these symptoms.

Minor allergic reactions to products (washing detergent, creams, perfume), food, or plant reactions (stinging nettles) can be safely treated with over-the-counter antihistamines and should get better in hours to days. Make sure to avoid whatever caused the reaction in the future.

If you find that you are getting regular allergic reactions and do not know the reason why, you should discuss it with your doctor, and you may benefit from getting allergy testing.

Sedating antihistamines

Older antihistamines are more likely to cause drowsiness – this may be an advantage if symptoms are worse at night, but not if you need to operate heavy machinery or drive long distances. Those containing chlorpheniramine or diphenhydramine (such as Benadryl) are older types.

They work for a shorter amount of time, typically 4 to 6 hours, so you might need to take them several times a day or just when the pollen count is higher, typically early mornings and evenings. Despite this, some people think they work better for their particular hay fever – it's a question of trial and error on what works for you.

Some antihistamines that cause drowsiness are also found in over-the-counter sleeping tablets, such as diphenhydramine.

Non-sedating antihistamines

Once-daily antihistamines are available to buy and contain loratadine, fexofenadine, levocetirizine, or cetirizine. They are similar in effectiveness, but you may find one works better than another. They get to work within 1 to 3 hours, peak in effectiveness after 8 to 12 hours, but last for at least 12-24 hours. At the recommended doses, they are unlikely to make you drowsy.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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