I understand xyzal (levocetirizine) and dallergy are both antihistamines, but what is the difference between the two?

Side effects: Dallergy (http://www.Drugs.Com/cdi/dallergy.Html) is a brand name product composed of 2 different drugs, one of which is a 1st generation antihistamine, which can make you sleepy among other side effects, plus a decongestant, which can raise your blood pressure. Xyzal (http://www.Drugs.Com/xyzal.Html) is a brand name for levocetirizine which is a left mirror image of zyrtec which contains l&r.

Drowsiness: D'allergy is one of the older antihistamines that are more likely to cause drowsiness. Also, xyzal (levocetirizine) lasts much longer; you will control your symptoms better over time xyzal (levocetirizine).