See also: The long-lasting effects of Allegra D
Allegra is an effective antihistamine. However, Allegra D is nearly worthless. Allegra D is 60 mg fexofenadine combined with a time released dose of pseudoephedrine. The problem is, a 60 mg fexofenadine dose only reduces histamine levels when applied directly to cells. For the average person, it takes around 160 mg for the chemical to work when actually ingested.
Thus, one must consume 3 Allegra D's to make fexofenadine produce anything noticable, thereby also tripling the dose of pseudoephedrine. This will certainly cause many nasty side effects (anxiety, increased heart rate, and a nasty crash when the stimulant effects wear off). In other words, the drug companies messed up the ratios when combining these two chemicals, rendering the medication impractical for its intended use.
All information was acquired from a certified allergist