These antihistamines will not be discussed further.) Antihistamines also may be used to treat motion sickness, insomnia (difficulty sleeping), and anxiety.
Antihistamines work by blocking the effects of a chemical called histamine that is responsible for many allergic symptoms.
Patients who experience significant allergic symptoms regularly may take daily antihistamines to keep their symptoms under control.
Some antihistamines are found in combination pills that contain other medications.
For example, antihistamines are commonly combined with decongestants (for example, Claritin-D, Zyrtec-D, Allegra-D), a class of medicine that is used to dry up the nasal passages and relieve head congestion.