 [ Symptoms ] my doctor said to give benedryl to my son for his hives and the babysitter gave him zyrtec is this an issue  he has an appointment with the allergy doctor tomorrow to possibly do allergy testing is it going to cause an issue he is 4 years old and weighs 34 8lbs they gave him 34 tsp [ Disease ] both are antihistamines and both are safe for children of his age if the proper dose is given zyrtec lasts much longer benadryl lasts only about four hours