Allegra-D (fexofenadine / pseudoephedrine) can have more side effects (such as increased blood pressure and difficulty sleeping) than Allegra since it has pseudoephedrine in it. If you have severe high blood pressure or heart disease you can't take this medicine. Allegra D’s active antihistamine ingredient is fexofenadine, while Claritin D uses loratadine. Fexofenadine is not for everyone and should not be administered to children under 2 without a doctor’s recommendation, according to the National Library of Medicine. For example, while Claritin is effective for treating hay fever and hives, other antihistamines, such as Zyrtec and Allegra, work better and faster and last longer. For example, Zyrtec and Allegra work quickly for the treatment of allergic rhinitis and hives, typically within less than an hour. Claritin (loratadine) and Allegra are both new generation antihistamines while the d is pseudoephedrine, a decongestant. Typically one or the other medication should be sufficient, although there are no drug interactions or side effects. Allegra and Claritin interact with some of the same drugs. Specifically, each may interact with ketoconazole and erythromycin. But Allegra can also interact with antacids , and Claritin can also. Claritin-D is used to treat sneezing, runny nose, itchy eyes, hives, itching, and other symptoms of allergies and the common cold. Learn about side effects, interactions and indications. Learn about side effects, interactions and indications. Claritin-D® and Allegra-D® are available behind-the-counter because they contain pseudoephedrine. Check with a pharmacist or physician before using any new medication or drug. Check with a pharmacist or physician before using any new medication or drug. Clear, transparent answers from Doctors: Dr. Frasie delves into whether or not you should take Claritin and Allegra together for symptom relief. Clear, transparent answers from Doctors: Dr. Frasie delves into whether or not you should take Claritin and Allegra together for symptom relief. Compare Allegra D vs. Claritin D, which is better for uses like: Allergy, Cough and Sneezing. Compare head-to-head ratings, side effects, warnings, dosages, interactions and patient reviews. Patients rated Claritin D 3.5/5 over Allegra D 3.4/5 in overall satisfaction. Allegra-D (fexofenadine / pseudoephedrine) is a combination allergy medicine that's useful if you have congestion and runny nose. Claritin-D (loratadine / pseudoephedrine) relieves allergies and congestion without causing daytime sleepiness but it can keep you up at night.