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First-generation antihistamines

Dr Roger Henderson
Reviewed by Roger HendersonReviewed on 29.04.2024 | 3 minutes read

Antihistamines are commonly used to help treat allergy symptoms but can also be used to treat a variety of conditions such as insect bites, motion sickness, or even to help with sleep. They reduce sneezing, a runny nose, skin rashes or itching, but are usually less effective for nasal congestion. Antihistamines are widely available over-the-counter in many pharmacies and shops, but some are only available on prescription.

There are two types of antihistamines – first-generation (drowsy) and second-generation (non-drowsy). First-generation antihistamines are the first kind that were developed. They can make you feel sleepy and are useful if your allergy symptoms keep you up at night. They also help with travel or motion sickness. Common first-generation antihistamines include chlorphenamine (Piriton), promethazine (Phenergan) and cinnarizine (Stugeron).

Doctor’s advice

Who is it for?

Antihistamines are useful to ease your allergy symptoms and are beneficial if you suffer from allergic conditions like hives, drug allergies, itchy skin conditions, hay fever and more. They can also help ease cough and colds, nausea and motion sickness, vertigo, and insect bites.

The most common side effect of first-generation antihistamines is drowsiness and can be especially useful if your symptoms affect your sleep. Promethazine (Phenergan), cinnarizine (Sturgeon) and cyclizine can also be purchased over-the-counter for travel sickness.

How do they work?

Antihistamines work by blocking the actions of a chemical called histamine in the body. Histamine is made by the body’s immune system to attack allergens that you are exposed to. Too much histamine can cause irritation and inflammation in many organs such as the nose, throat, lungs, and skin; resulting in the traditional “allergy symptoms” of itchiness, swelling and redness.

First-generation antihistamines differ from their newer counterparts due to their chemical structure allowing them to cross the blood-brain barrier and block the histamine receptors in the brain. This results in the sedating side effect, unlike second-generation antihistamines which selectively targets peripheral histamine receptors. First-generation antihistamines also target the part of the brain that controls nausea and vomiting, thus can also be used to prevent motion sickness.

Should anyone avoid taking it?

First-generation antihistamines may cause drowsiness, dizziness and blurred vision. Do not drive or use heavy machinery after taking these medicines. Concurrent use with alcohol should also be avoided, as this enhances the drowsy effects. Like any other medicine, do not take these if you are hypersensitive to antihistamines or to any of the other ingredients.

Medical advice from a doctor or pharmacist should be sought before purchasing antihistamines for children or the elderly, those who are pregnant or breastfeeding, people suffering from serious medical conditions (eg. epilepsy, high blood pressure, glaucoma, heart disease, breathing problems, kidney/liver disease etc.), and people that use other prescription medications.

Are there any side-effects?

Some common side effects include;

  • Drowsiness, dizziness, and reduced co-ordination and reaction speed · Tiredness · Headaches · Blurred vision · Dry mouth
  • Difficulty passing urine

The leaflet that comes with your medicine will give a full list of possible side effects and advice about when to get medical help depending on what product you have purchased.

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Dr Roger Henderson
Reviewed by Roger Henderson
Reviewed on 29.04.2024
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