23rd June, 20204 min read

Antihistamines: What’s available and what are the side effects?

Medical reviewer:Healthily's medical team
Author:Alex Bussey
Last reviewed: 24/06/2020
Medically reviewed

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Antihistamines are a group of medicines that are often used to manage allergic conditions like hay fever, hives, eczema or allergic conjunctivitis.

They can also be used to relieve symptoms of motion sickness, nausea and insect bites.

Antihistamines work by blocking the effects of histamine -- a chemical that helps your body fight off infections by making your blood vessels more leaky to allow more white blood cells (that protect against infection) to reach the affected area.

However, people with allergies release histamine when they’re exposed to something harmless, like pollen or house dust, triggering an allergic reaction that can irritate your throat, eyes, lungs, sinuses, digestive system or skin.

Taking antihistamines can relieve this, but you may be wondering which one is best to take, as there are many different types

What types of antihistamine are there?

Antihistamines are normally divided into 2 distinct categories:

  • sedating antihistamines
  • non-drowsy antihistamines

Sedating antihistamines are able to cross the blood-brain barrier and make you feel drowsy, also affecting your coordination, movement and concentration.

Non-sedating antihistamines are less likely to enter your brain and tend to cause less drowsiness as a result.

Both types of antihistamine are available from pharmacies, and are normally found in a variety of forms, including tablets, capsules, syrups, eye drops and nasal sprays. You may need a prescription to buy certain antihistamines.

Some commonly used antihistamines include:

Sedating antihistamines Non-drowsy antihistamines
alimemazine acrivastine
chlorphenamine maleate cetirizine hydrochloride
clemastine desloratadine
cyproheptadine hydrochloride fexofenadine
hydroxyzine levocetirizine
promethazine loratadine

Which type of antihistamine is best?

Both types of antihistamine can be equally effective at treating a wide variety of allergy symptoms, so the right choice for you normally depends on whether you want a sedating or non-sedating medication.

It may also depend on the condition that you are trying to treat.

Hay fever - woman sneezing

Hay fever and allergic rhinitis

Hay fever and other allergic conditions that affect the nose, throat and eyes are normally treated with non-drowsy antihistamines like cetirizine or loratadine as these medicines are less likely to make you feel drowsy or tired.

But you may need to try both types of medication before you find an antihistamine that works well for you.


Hives (urticaria) and other allergic skin conditions are normally treated with non-drowsy antihistamines like cetirizine, fexofenadine, or loratadine.

You may find it helpful to take a sedative antihistamine like promethazine if you're struggling to get to sleep because of an itchy rash or skin condition.

Motion sickness and nausea

Antihistamines like cyclizine can also be used to treat nausea, motion sickness and vertigo. It is believed that they work on the part of your brain that controls nausea and vomiting.

Itchy eyes

If you have itchy eyes, you may find that it helps to use antihistamine eye drops that contain a non-drowsy antihistamine like ketotifen or azelastine. These antihistamines are fast-acting, and less likely to make you drowsy.

Itchy eyes

What are the side effects?

Sedating antihistamines will make you feel drowsy and sleepy and may also affect your coordination, movement and concentration.

If you take these, you should not drive, cycle or operate machinery. Other side effects can include a dry mouth, blurred vision or difficulty peeing.

Although they are less likely to cross the blood-brain barrier, non-drowsy antihistamines can still make some people feel drowsy or tired, especially if they are combined with alcohol or taken in large doses.

If you take a non-drowsy antihistamine and you start to feel tired or sleepy, you should also not drive, cycle or operate machinery.

Other side effects associated with non-drowsy antihistamines include headaches, a dry mouth or nausea.

Antihistamines can also interact with certain medications. If you are worried about the side effects or you are unsure about whether or not it is safe for you to take an antihistamine, ask your doctor or see a pharmacist for advice.

How should I take antihistamines?

Most people can take non-prescription antihistamines without experiencing any serious side effects, but you should always follow the instructions supplied with your medication and talk to a pharmacist if you are worried.

You should also talk to a doctor or a pharmacist if you:

  • are pregnant or breastfeeding
  • are looking for an antihistamine for a young child
  • are taking other medications
  • have an underlying or chronic health condition like heart disease, liver disease, kidney disease or epilepsy

Read more about the different types of antihistamine and how they work.

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