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Drowsy antihistamine

Written by Caidr's team of doctors and pharmacists based in UK | Updated: 22.02.2023 | 2 min read

Antihistamine tablets are a group of medications that prevent the level of histamine from rising in our 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 drowsy or non-drowsy. With drowsy antihistamines, care should be exercised when driving or operating heavy machinery, and alcohol should be avoided. Below, Caidr's pharmacists will go into more detail about the different antihistamines and their side effects.

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 for you.

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.

Drowsy 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-drowsy 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, and peak in effectiveness after 8 to 12 hours, but last for at least 12-24 hours. The recommended doses are unlikely to make you drowsy.

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