Antihistamines

What are antihistamines?

Antihistamines are a class of medication that commonly treat allergy symptoms, like runny nose, sneezing and itchy eyes. They can also treat some digestive conditions.

Most antihistamines are over-the-counter (OTC) medications, but they also come in prescription form. Antihistamines are also common ingredients in the following OTC medications:

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• Cold and flu products.
• Decongestants.
• Cough suppressants.
• Pain relievers.

Antihistamines work by blocking histamine receptors. “Anti-” means “against.” Histamine is a chemical your immune system releases to send messages between different cells. Histamine has several functions, but it’s mainly known for its role in causing allergic and anaphylactic symptoms. Allergic reactions can happen due to several substances (allergens), including:

• Environmental allergens, like pollen, dust, mold and pet dander.
• Insect bites and stings.
• Foods.
• Medications.

Antihistamines can help manage all these allergies.

What are the types of antihistamines?

Healthcare providers divide antihistamines into two major subtypes based on which histamine receptors they block:

• H1 receptors.
• H2 receptors.

H1 receptor antihistamines

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You have H1 receptors throughout your body, including in neurons (brain cells), smooth muscle cells of your airways and blood vessels. Activation of the H1 receptors causes the well-known allergy and anaphylaxis symptoms. So, H1 receptor antihistamines mainly treat allergy symptoms.

The U.S. Food and Drug Administration (FDA) has approved the use of H1 antihistamines to help treat the following conditions:

• Allergic rhinitis (hay fever).
• Allergic conjunctivitis (pink eye).
• Allergic skin reactions, like atopic dermatitis (a condition that causes skin rashes and itchiness).
• Sinus infection (sinusitis).
• Hives.
• Angioedema (skin swelling that often happens from an allergic reaction).
• Bronchitis.
• Motion sickness.
• Nausea.
• Vomiting.

Healthcare providers may also use H1 antihistamines to treat insomnia. This is an off-label use of the medication.

The H1 antihistamines further break down into two groups:

• First-generation antihistamines.
• Second-generation antihistamines.

First-generation antihistamines generally have more side effects than second-generation antihistamines because of how they work. First-generation antihistamines more easily cross your blood-brain barrier into your central nervous system. This causes drowsiness. Second-generation antihistamines are generally safer because they don’t cause drowsiness and interact with fewer medications.

List of first-generation antihistamines for allergies

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A few examples of first-generation H1 antihistamines include:

• Brompheniramine chewable tablets (BroveX CT®).
• Chlorpheniramine tablets (like Ahist®,Aller-Chlor® and Chlor-Trimeton®).
• Clemastine tablets (Dayhist®, Tavist Allergy®).
• Cyproheptadine oral liquid (Periactin®).
• Dimenhydrinate chewable tablets (Dramamine®).
• Diphenhydramine capsules or tablets (like Alka-Seltzer Plus Allergy®, Benadryl® and Vicks ZzzQuil Nighttime Sleep-Aid®).
• Doxylamine tablets (Unisom®).
• Hydroxyzine capsules or tablets (Atarax®, Rezine® and Vistaril®).

List of second-generation (non-drowsy) antihistamines for allergies

A few examples of non-drowsy H1 antihistamines include:

• Azelastine eye solution (Optivar®)
• Azelastine nasal spray (Astelin®, Astepro®).
• Cetirizine tablets (Zyrtec®).
• Desloratadine (Clarinex®).
• Fexofenadine (Allegra®).
• Loratadine capsules or tablets (Claritin®).

H2 receptor antihistamines

You have H2 receptors mainly in the cells in your stomach that release acid, smooth muscle cells and heart cells. So, H2 antihistamines treat certain gastrointestinal (GI) conditions.

The FDA approves H2 antihistamines to help treat the following conditions:

• Peptic ulcer disease.
• GERD (chronic acid reflux).
• Gastritis.
• Zollinger-Ellison syndrome.

Healthcare providers may also use H2 antihistamines to treat indigestion. This is an off-label use of the medication.

List of antihistamines for digestive conditions

If you’re taking an antihistamine to help with stomach issues, you’re likely taking an H2 antihistamine. A few examples include:

• Cimetidine (Acid Reducer®, Tagamet®).
• Famotidine (Pepcid®).
• Nizatidine (Axid®).

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