Antihistamine pills such as diphenhydramine hydrochloride (Benadryl) or chlorpheniramine maleate (Chlor-Trimeton) are included in allergy kits to stop or reduce itching, hives, sneezing and wheezing, and other symptoms caused by an allergic reaction. They are not a substitute for an epinephrine shot.

Many allergic symptoms, such as hives and wheezing, occur when a chemical called histamine is released as part of the allergic reaction to an allergen. Antihistamine medicines block the release of histamine.

Antihistamines can make people sleepy or make it harder for them to concentrate. These medicines should be used carefully by people who need to drive or operate heavy machinery. Other side effects include dry mouth, nausea and vomiting, restlessness or irritability (especially in children), inability to urinate, and blurred vision.

Don't give antihistamines to your child unless you've checked with the doctor first.