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What is a Histamine Blocker?

Karyn Maier
Updated Mar 03, 2024
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A histamine blocker is a type of medication that modifies the activity of histamine, a specialized amine that functions as a neurotransmitter and an inflammatory mediator. Histamine blockers are often referred to as antihistamines. However, this term is misleading. For one thing, these medications do not block the synthesis of histamine from the amino acid histidine as the term implies, nor do they prevent its release from mast cells. Instead, a histamine blocker is designed to prevent targeted receptor sites from accepting the chemical’s attachment, as well as the instructions it’s programmed to deliver.

There are two types of histamine receptors that receive histamine, but they respond differently. H1 receptors are involved in inflammatory reactions and produce symptoms commonly seen in allergic reactions, such as swelling, sneezing, and increased nasal secretions. Therefore, an H1 histamine blocker, also known as an H1 antagonist, is given to treat allergies. H2 receptors, on the other hand, are involved in regulating the secretion of gastric acid from parietal cells located in the lining of the stomach. So, an H2 histamine blocker, or H2 antagonist, is used to prevent excess production of stomach acid and is intended for the treatment of peptic ulcers and gastroesophageal reflux disease (GERD).

Examples of common blockers that act upon H1 receptor sites include diphenhydramine (Benadryl®), loratadine (Claritin®), and chlorpheniramine (Chlor-Trimeton®). Some of these medications, particularly first generation drugs like diphenhydramine and chlorpheniramine, also impact H1 receptors in the brain, which triggers a sedative effect. However, some of the newer medications, like loratadine, produce far less drowsiness because these drugs cannot pass though the blood-brain barrier as well as their predecessors. The most commonly used H2 blockers are cimetadine (Tagamet®) and ranitidine (Zantac®). These medications are available without a prescription.

While these medications are very effective and considered safe, they are not without risk and side effects. For example, some of these drugs produce drowsiness and may interfere with the ability to drive or operate machinery, an effect enhanced with alcohol consumption. In contrast, non-sedating blockers may produce insomnia in some people. Other common side effects include dry mouth, dizziness, hyperactivity, irregular heartbeat, flushing of the skin, and stomach cramps. In addition, the prescription-based drug cimetidine is contraindicated with warfarin (Coumadin®) and other blood thinners due to an increased risk of bleeding, increases serum levels of many other medications, such as calcium channel blockers and cholesterol-lowering drugs, and is known to pass through breast milk.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Karyn Maier
By Karyn Maier
Contributing articles to The Health Board is just one of Karyn Maier's many professional pursuits. Based in New York's Catskill Mountain region, Karyn is also a magazine writer, columnist, and author of four books. She specializes in topics related to green living and botanical medicine, drawing from her extensive knowledge to create informative and engaging content for readers.
Discussion Comments
By anon332853 — On May 01, 2013

Quercetin, which is a natural antihistamine, as well as a bio-flavenoid works extremely well with seasonal allergies. One 500mg. capsule will help you sail through without having to take H1 blockers.

By indigomoth — On Jun 28, 2011

@umbra21 - I agree it is better to get them from a doctor. If you have chronic allergies though, you might want to ask about getting a more permanent fix than just taking antihistamines.

There are some therapies now which use a kind of slow process of getting you used to an allergen in small amounts over time. I'm not sure how widely available this treatment is but it might be worth asking about.

Or you could try the natural histamine blocker, which is vitamin C.

It's not as effective as the medication but if you are in a pinch it's better than nothing.

By umbra21 — On Jun 28, 2011

I have to use histamine blockers all the time because of my allergies. I have a dust allergy which I can usually control just by making sure my surroundings are clean, but if I'm staying overnight somewhere, or in a place with a particular kind of pollen, I start sneezing and wheezing and can't stop.

I find them incredibly expensive to buy, considering you need to take one every day.

But, if you go to the doctor and ask him to prescribe you some antihistamine tablets they are a lot cheaper, more effective and you can get them in more bulk.

I'm not sure if the drug store price is because they can be used in making drugs or what, but if you need them regularly, get the prescription.

Karyn Maier
Karyn Maier
Contributing articles to The Health Board is just one of Karyn Maier's many professional pursuits. Based in New York's...
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