Antihistamines are medicines that may relieve allergy symptoms and itching. Many are available without a prescription. Nondrowsy antihistamines include fexofenadine (Allegra) and loratadine (Claritin). Antihistamines like diphenhydramine (Benadryl) and chlorpheniramine (Chlor-Trimeton) can make you feel sleepy and cause other side effects. They may not be safe for young children or people who have certain health problems.