where to purchase Depakote Since allergy season is ramping up, it is important to know which oral antihistamine is best for you based on side effects of the drugs and your symptoms. All antihistamines work by reducing your symptoms of itching, sneezing, and runny nose. Keep in mind that these drugs will have little effect on nasal congestion. Antihistamines, such as, diphenhydramine, or Benadryl, can cause sedation, cognitive impairments, dry mouth, constipation, and blurry vision. Other antihistamines, such as cetirizine (Zyrtec), loratidine (Claritin), and fexofenadine (Allegra), cause less sedation. When taking Allegra, avoid taking it with juices and multivitamins. If you are pregnant and need to use one of these agents, Zyrtec and Claritin are considered low risk medications. And as always, ask your pharmacist to help you select the best drug for you! We are happy to help!