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Describe how antihistamines work.

1 year ago

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Saul Hettinger


20 Replies

Gurjeet C Profile Picture
Gurjeet C Best Answer!

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Histamine is a Monoamine Neurotransmitter, which is formed via the decarboxylation of the amino acid Histidine. Histamine acts on H1-Histamine receptors which are dispersed throughout the body, most prominently on endothelial cells of capillaries and in mucous membranes such as those found in the Nasal, Oral and Pharyngeal cavities. Histamine is produced by granulocytes such as Basophills as well as Mast cells, these cells secrete Histamine in response to IgE activation upon the binding of foreign bodies such as pollen or dust. This results in the production of nitrous oxide by endothelial cells causing capillary lumen dilation and increased capillary permeability. This mechanism is responsible for symptoms such as a stuffy nose, increased mucous production and inflammation around the eyes. Antihistamines such as Cetrizine, Loratidine, Chloramphenicol, and Fexofenadine act as H1 receptor antagonists which prevent the binding of Histamine to its target receptor which inhibits the immune response which causes the symptoms of hayfever. Older antihistamines such as Diphenhydramine and Promethazine are no longer used due to their ability to cross the blood-brain barrier and antagonise H1 receptors of the Reticular Activation Centre which is responsible for alertness and stimulation of the frontal cortex of the forebrain. These older generation antihistamines are now re-branded as sleeping aids for insomnia.


Histamine is not only responsible for the modulation of allergic immune responses, it also plays a key role in the secretion of HCL by the Parietal cells of the Gastric glands of the stomach mucosa. However, Parietal cells do not express H1 histamine receptors but rather H2 histamine receptors. H2 antagonists such as Ranitidine were used in the management of acid reflux and gastritis since they reduced Gastric acid production. In modern medicine proton pump inhibitors such as Omeprazole and Lansoprazole are used more commonly.

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Faiza Suleman Best Answer!

antihistamines block the effect of histamines in your body. histamine is released after the body encounters harmful substances such as an infection

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Selene Basso Best Answer!

Target mast cells and basophils (both a type of blood cells) that release histamine and trigger an allergic reaction.

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Kieron Brand Best Answer!

Hi saul!


Antihistamines work by blocking the histamine receptor on special cells called mast cells. Histamines cause something called "degranulation of mast cells". All this means is that the contents of the cell that cause inflammation are deposited into the blood and surrounding tissues.

Therefore if you block the histamine receptors then these substances that cause inflammation are not released from the cell.

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Toby Best Answer!

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Histamine is a molecule that binds to cell receptors, often causing "allergy" symptoms like sneezing and coughing. Antihistamine medications act as a competitive inhibitor - the antihistamine molecules will bind to the receptors instead of the histamine molecules, reducing the severity of symptoms.

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Danielle Best Answer!

Antihistamines effectively block the effects of a chemical called histamine. These effects are often characterised by inflammatory responses, such as urticaria (hives) or blocked sinuses. Histamine is released when the immune system is exposed to an allergen or a xenobiotic. Antihistamines will block released histamine from binding to receptors, thus reducing symptoms.

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Sofia Ali Best Answer!

Antihistamines are a drug class which work to treat a variety of medical issues. These include allergic rhinitis (runny nose), common cold, influenza and other allergens.


The mechanism of action for antihistamines is competitive receptor antagonism. Antihistamines prevent histamine from binding to H1 receptors and therefore preventing the outcome of the issues.

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Reem Agel Best Answer!

Antihistamines work by blocking the effects of histamine in the body. This substance is normally released when the body detects something that is potentially harmful such as an infection; histamine causes blood vessels to expand and swelling of the skin, which aids to protect the body.

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Diya Singh Best Answer!

Firstly, break down the process. Start with histamine. What is Histamine? It is a substance that your body produces when it detects something unusual/ harmful. So when this is released, the body reacts and produces an allergic reaction (Skin swelling, blood vessels expanding and all that). So then to counter that, us doctors prescribe a drug that contains antihistamines. These then go to the histamine "Channels" and block the effect of histamine so we do not have that "allergic reaction".

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Ernest Agyekum Wiafe Best Answer!

Antihistamines are drugs used to stop the allergic effect of histamine , a substance produced in the body as a result of the body contact with allergic substances such as pollen, bee sting etc

Jemimah M Profile Picture
Jemimah M Best Answer!

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Histamine is a chemical messenger involved in a number of complex biological actions. It occurs mainly in an inactive bound form in most body tissues. When released, it interacts with specific histamine receptors on the cell surface. There are four types of histamine receptors  H1, H2, H3, and H4.


Antihistamines are usually synthetically manufactured drugs that inhibit the effects of histamine by binding to the receptors.


H1 Antihistamines inhibit the action of histamine by competitively binding to the receptors and therefore blocking histamine from binding to H1 receptors. (these are usually used to relieve allergic reactions like hay fever)


Histamine also has a role in the regulation of the secretion of acid in the stomach. H2 antihistamines are very effective in the regulation of the secretion of acid and the hormone gastrin. They are therefore great for treatment of peptic ulcers (a condition caused by excessive secretion of gastric acid) .


Each antihistamines target the same receptor as the histamine thus inhibiting the effects of it e.g allergies or ulcers

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Andreea Luchian Best Answer!

First, we have to understand how histamines work. Histamines work by inducing an increased level of vascular permeability, which leads to fluid moving from capillaries into the surrounding tissues. This further leads to increased swelling and vessel dilation. This effect can be stopped by antihistamines by antagonising the H-1 receptors and this translates into a clinical benefit, namely a reduction in allergy symptoms


Hadiqa M Profile Picture
Hadiqa M Best Answer!

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During an allergic response white blood cells of the immune system, specifically mast cells, release a neurotransmitter called histamine. Histamine production in the body encourages inflammatory reactions to occur and this is what triggers the symptoms we experience during an allergic reaction or infection, such as itchy eyes, runny nose and sneezing.


Antihistamines are a group of medications that play a role as selective H-1 receptor antagonists. They work by blocking H-1 receptor sites; this leads to a blockage in histamine production. Additionally, the inflammatory response in the body is also then suppressed and this therefore allows us to control the symptoms we feel during an allergic response.

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Roshni R Profile Picture
Roshni R Best Answer!

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Anti-histamine work by inhibiting the effects of H1 receptors. They are a class of drugs commonly used to treat the symptoms of an allergic reaction such as swelling and itching etc.

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Dominika K Profile Picture
Dominika K Best Answer!

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Histamine is released in the body in response to harmful mediators, for example during an infection or an allergic response. It causes vasodilation and swelling. Antihistamines block histamine receptors and reduce swelling and are therefore taken to relieve symptoms of allergies, such as hay fever and reactions to bites or stings.

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