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How Do Antihistamines Work?

 Find out the science behind these popular anti-allergy medications

By
Sanaz Majd, MD,

If you suffer from seasonal allergies, the first line of treatment for your symptoms is antihistamines. 

Antihistamines block the release of histamine (an inflammatory substance) from the white blood cells, and so can prevent all of the annoying allergy symptoms.  

Unfortunately, any medication taken by mouth is distributed all over the body, not just to where it is needed. So these medications can have significant side effects. Older antihistamines, like Benadryl, are significantly sedating. One study showed that people taking Benadryl were more impaired while driving than were those who had drunk too much. Fortunately, newer antihistamines like Claritin, Allegra, and Zyrtec are less sedating (although some people get side effects even with these medications). All antihistamines are best if taken regularly, as they prevent the release of histamine but don’t help much once it’s been released.

Sneezing image courtesy of Shutterstock.

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