Allegra-d, zyrtec-d, claritin-d: what do they have in common? Pseudoephedrine, brand name sudafed. This is a decongestant that relieves sinus headaches and pressure. The antihistamine is what makes the three different. Allegra is fexofenadine, which is a newer antihistamine that is considered nondrowsy, while zyrtec and claritin (certirizine and loratadine, respectively) are considered "drowsy" like benadryl (diphenhydramine). Zyrtec and claritin shouldn't make you drowsy, but they can. Anywho, the antihistamine is what helps the sneezing, itchy nose/eyes, runny nose, etc. The decongestant helps the sinuses clear, which will help the headaches. If you have not taken a medication that specifies the d, you havent taken one for your symptoms. I've been on allegra-d for about 18 months and have only had one sinus infection since starting it. Before I had several a year.