It also causes small blood vessels, or capillaries, in your mucus membranes to expand (dilate), which can cause nasal congestion.
An antihistamine relieves these symptoms by preventing histamine from attaching to cells’ histamine receptors.
The newer generation antihistamines, such as loratadine (Claritin), fexofenadine (Allegra), and cetirizine (Zyrtec), are generally a better choice since they’re less sedating than the older, “first-generation” antihistamines, such as diphenhydramine (sold under the brand name Benadryl).
Once available by prescription only, all three of the newer antihistamines are now sold over-the-counter, and you can save money by buying the store-brand (generic) version rather than the name-brand one.
If you’re among the many people who suffer from seasonal allergies, an antihistamine can be a key tool for relieving uncomfortable symptoms.
But not all antihistamines are created equal, and while they’re sometimes confused with decongestants, the two work very differently.
And some allergic reactions are too serious to treat with an antihistamine, though that’s a commonly made mistake, even in ERs.
Here are answers to help you sort the facts from the fiction on these important but sometimes misunderstood drugs.
(Your immune system perceives the substance as an invader and responds by releasing inflammatory chemicals.) Histamine triggers the classic, irritating symptoms of allergies: sneezing, itching, runny nose, and watery eyes.A shot of epinephrine acts rapidly (less than 10 minutes), compared with an hour or more for an antihistamine—too long to be effective in this emergency situation.Plus an antihistamine won't adequately treat the life threatening respiratory and blood pressure complications of anaphylaxis.We don’t recommend them because they can increase the risk of side effects, and because you often pay more for the combined drug when you could buy each separately.Note that people who have diabetes, prostate enlargement, uncontrolled hypertension, heart disease, or thyroid disease should generally avoid oral decongestants as they can cause adverse effects—including increased blood pressure or blood sugar, heart arrhythmias, and urinary problems—to which those groups are especially susceptible.That means you can control your symptoms with only 1 or 2 doses each day compared with older medications, which usually require doses every 4 to 6 hours to maintain their effectiveness.