General Question

El_Cadejo's avatar

How do allergy medicines work?

Asked by El_Cadejo (33966 points ) October 7th, 2009

I got thinking about this the other day after i accidentally ate something with peanuts in it and had to have some benadryl to stop me from having a bad reaction. yay allergies. So i thought, i’ve been taking benadryl my whole life and it always cures me, but i really have no clue how it works.I mean my body for some reason thinks peanuts are bad, what is it in benadryl that tells my body “nahhhh its all cool”

How do preventative allergy medicines work too? (claritin, allegra ect…) Why are we able to make preventative allergy medicines for some allergens, but not others? What is different about them?

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3 Answers

Dr_C's avatar

Antihistamines block the effects of histamine by “coating” receptors, which prevents binding. This, in turn, prevents nasal allergy symptoms.

Histamine works quickly once released. By the time your symptoms appear, the histamine has already attached to cell receptors, and the allergic reaction is well under way. That’s why you need to take antihistamines 2 to 5 hours before exposure to allergens. Or you need to take them on a regular basis.

Some antihistamines go to work 15 to 30 minutes after they’re taken. They reach their peak effectiveness in 1 to 2 hours. If you take an antihistamine before you’re exposed to your allergens, the allergic reaction can be stopped.

Edit: Per Shilolo’s request… source

La_chica_gomela's avatar

Great question! I don’t have an answer. I’m also curious, especially how Nasonex works. It works for me like a thousand times better than any other allergy medicine I’ve ever taken.

shilolo's avatar

The non-sedating antihistamines (claritin, allegra, zyrtec) and the more treatment oriented ones (like benadryl) both work by inhibiting the activity of the chemical histamine at the histamine receptors known as H1 receptors. However, the major difference is that the non-sedating ones only act at peripheral receptors whereas benadryl acts peripherally and in the central nervous system. The central nervous system effects are what lead to the drowsiness.

As for the preventative ones, like Nasonex and Flonase, those are nasal steroids that suppress the activity of T and B-cells in the nasal mucosa. Thus, the cells are less reactive to allergens, fewer antibodies are produced, and mast cells degranulate less frequently, leading to fewer symptoms. A little known fact is that studies show that the preventative nasal steroids are superior to treatment with antihistamines during episodes. Furthermore, they can also help with itchy eyes, if that is a symptom too, though patanol eye drops help with that as well.

Also, there are some newer types of anti-allergy and asthma medications such as leukotriene inhibitors that act via a different mechanism altogether.

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