Antihistamine tablets 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 medications block the release of histamine.
Antihistamines can make people sleepy or make it harder for them to
concentrate. These medications 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.