About Antihistamines

Antihistamines: Everything you need to know

Antihistamines are medicaments that are designed to block the receptor of histamine which in turn halts the symptoms caused by histamine such as runny nose, swollen throat, sneezing, and itchy eyes. Histamine is a chemical substance that is produced in the body system and accumulates in allergic cells like basophils and mast cells. When people have allergies, histamine is usually released from the allergic cells in response to the allergens. Histamine attaches to the histamine receptor which is situated on different cells of the body and cause allergic symptoms like hives, anaphylaxis, sneezing, itchy note, and itchy eyes.

What are Antihistamines used for?

Antihistamines are usually used for treating different allergic diseases. They come in different forms such as nasal spray, oral, injection, and eye drop forms. Antihistamines can be used for the treatment of the following diseases:


The main treatment for Hives (urticaria) is oral antihistamines. The newer and low-sedating forms of antihistamines are usually favoured above the older forms which are more sedating. The newer forms include Claritin and Zyrtec, while the older forms include Atarax and Benadryl. It is important to mention that topical Antihistamine cream that is present in many of the OTC anti-itch creams, like Benadryl cream, should not be administered as a treatment for hives and other skin allergies. This is because topical Antihistamines usage on the skin can lead to contact dermatitis as a result of the presence of Antihistamine.

Hay Fever

Hay fever, also known as allergic rhinitis, can be treated with the newer form of oral antihistamines. Medications in this category include Levocetirizine (Xyzal), Fexofenadine (Allegra), Cetirizine (Zyrtec), and Desloratadine (Clarinex). These medications are highly effective in the treatment of hay fever. Other older antihistamines such as Chlorpheniramine (Chlor-Trimeton), Diphenhydramine (Benadryl), and Hydroxyzine (Atarax) are also effective in treating hay fever. However, they come with many side effects. Oral Antihistamines are very effective when taken on need-basis. This means that allergy symptoms significantly improve within a couple of hours after using the medication. Antihistamines medications are also available in the form of nasal spray which is used for the treatment of nasal allergies (allergic rhinitis). Nasal sprays in this category include Olopatadine (Patanase), and Azelastine (Astelin). There is also Corticosteroid nasal spray which is also used for the treatment of allergies. Medications in the category of corticosteroid for treating allergies include fluticasone Propionate (Flonase), Triamcinolone (Nasacort Allerfy 24 Hour), Budesonide (Rhinocort), and Mometasone (Nasonex)

Eye Allergies

Symptoms of eye allergies are usually treated with oral Antihistamines. These forms of Antihistamines are also made available as eye drops such as emedastine (Emadine), azelastine (Optivar), ketotifen (Alaway), and pheniramine (Visine-A). There are also some corticosteroid eye drops that may be used for the treatment of eye allergies when antihistamines are not effective. Corticosteroid eye drops in this category include Prednisolone (Omnipred), Fluorometholone (Flarex), and Loteprednol (Alrex).

Other Usages of Antihistamines

There are other allergic conditions that Antihistamines can be prescribed for. It is important to mention that the effectiveness of these medications on other allergic conditions might not be as effective as for the treatment of hay fever. These other allergic conditions include itching of the skin (pruritus), the common cold, anaphylaxis, insect bites and stings, and allergic reactions to other medications.

Popular Oral Antihistamines

There are some oral Antihistamines that are very common. These are the over-the-counter types and the prescription only types.

Over-the-Counter Oral Antihistamines

These are the most common and popular form of oral Antihistamines, such as Benadryl. Benadryl is a sedating and older form of Antihistamine. Although Benadryl is a good medicine for the treatment of different types of allergic conditions, its side effects reduces its regular usage, especially in daytime. Many older Antihistamines, such as Benadryl and Chlorpheniramine (Chlor-Trimeton) are present as OTC without doctor's prescription. Less-sedating Antihistamines are the newer forms, and they are also available over-the-counter. Medications in this category include Allegra, Zyrtec and Claritin. Newer forms of antihistamines cause less sedation and are usually preferred over the older forms that are more sedating.

Prescription-Only Oral Antihistamines

Atarax is the only older, sedating Antihistamine that is available as a prescription drug. Atarax is very sedating and is usually prescribed for treating skin allergies such as itching and hives. It is important to mention however that the active metabolite of Atarax is also available as an OTC drug, and it causes less sedation. Clarinex and Xyzal are two low sedating antihistamines that are also available through prescription.

Side Effects of Antihistamines

The older forms of Antihistamines like Atarax and Benadryl have a high amount of anticholinergic reactions which cause side effect. Some of these effects are drowsiness, headache, dry mouth, urinary retention, and constipation. Due to these side effects, these medications are considered to be highly sedating and are not recommended for regular daytime usage. Older Antihistamines have the potential to weaken your motor and mental functioning, thereby, reducing your ability to operate heavy machinery or motor vehicles. It is therefore advised that you do not handle any such device when using these medications. Many of the newer and less-sedating Antihistamines have low anticholinergic side effects, although some of these medications can still cause dry mouth or drowsiness. Claritin and Zyrtec are low sedating Antihistamines that have low adverse effects. Allegra on the other hand is the only Antihistamine that is considered to be totally non-sadating.

Apart from dry mouth and sedation, another side effect of Antihistamines is increased appetite which ultimately results in weight gain. This side effect may be as a result of the similar chemical structure of certain psychiatric medications and Antihistamines, like anti-depressants, known to increase users' appetite. As a matter of fact, Cyproheptadine (Periactin), an older form of Antihistamine, is usually prescribed for the main purpose of increasing the appetite of underweight children to result in weight gain.