There are two generations of antihistamines on the market.

The first generation includes the ones that cause drowsiness. These enter brain and have central effects besides the antihistamine ones. They are derived chemically from the phenothiazines (antipsychotics). This is why some like Vistaril, are used as sedatives. Dramamine orig formula, Benadryl, ChlorTrimeton, and Antivert (meclizine for dizziness) and Atarax belong to this class. All of these have multiple effects on various neurotransmitters, and are used for other things besides allergies. Benadryl is used for some forms of dyskinesia in fact.

Histamine is a neurotransmitter in the brain...it precedes release of serotonin and other neurotransmitters, and is considered a signaling molecule. So the first generation antihistamines affect many things, because they block histamine's job of initiating actions.

Claritin and Allegra, are second generation antihistamines, and much less potent or useful for allergies. And they do not cross into the brain, and have limited usefulness. In fact there are studies showing Claritin is equal to placebo in effectiveness!

Zyrtec (cetirizine is sort is inbetween the generations. It is a cousin of Atarax which is considered the most potent antihistamine for itching. It has some sedative actions but not as strong as Atarax.

Xyzal (levocetirizine) is related to Zyrtec and does not cross into the brain at all.

As the affinity to cross into the brain, is lost, so are the other actions that are common to the first generation drugs lost. So one would not expect Allegra or Claritin or Xyzal to work on drying things up like Benadryl does. If the runny nose is a Mast cell allergic response, they may work. But for all other causes, they would be ineffective.

A lot of good info. I see my Dr. again today and I will ask him what I should take or talk to him about some of these.
The Allegra D is a joke. The shot did nothing. My eyes water a lot too. I noticed that when I get out in the cold but my nose runs all of the time.

Mrs. D. I am on Metformin, Amitiza, and Nexium for my stomach. I only use the lidoderm patches when I am at my worst,same as the Methadone. I also have lidocaine gel around. I haven't taken the Methadone for awhile now. It really causes my stomach issues to be worse.

I also have a breathing problem. It's related to something else though besides the allergy. He diagnosed me with one last year. I don't breath deep enough.

Thanks,
Ada

thank you Mrs. D for that great information. My Lindsay has been on a lot of those with only the Benedryl really helping lately. She also was on Singular which is another one that is used for allergies. They put her on this for her Asthma.

Thank you again for your great information.

Sandy