I took Allegra for the first time in many many years yesterday due to acute chronic rhinitis and a serious asthma attack. I stopped taking Claritin after many years because it became ineffective. The same happened with Zyrtec. I do not tolerate decongestants. I live in south Florida, and my symptoms started with the colder than usual weather last week, and lots of blooming trees and plants. Windows and sliding doors have been open to let in fresh air. I had severe chills and the sweats all last night. However, the histamine blocker is working,so I am going to take another dose today. I used Flonase Sensimist last night too. In combination, they worked pretty well. I hope I don't get the chills again. If I do, I'll stop taking Allegra.