Antihistamines work by restricting the body from producing a chemical called histamine. The release of histamine in the body causes common allergic reactions such as sneezing, hives and an itchy throat. While antihistamines are primarily used to prevent and treat allergic reactions and hay fever, there are a few other uses for which they are commonly recommended. A doctor should oversee any use of medication.
Allergy Treatment
By restricting the release of histamine in the blood stream, antihistamines are able to treat the common symptoms of an allergic reaction. MayoClinic.com states that histamine can cause a person to itch, sneeze or produce excess mucus. Histamine can also cause the airways to constrict in a patient with allergy-induced asthma, leading to an asthma attack. FamilyDoctor.org notes that the most common antihistamines used to prevent and treat seasonal allergies are second generation antihistamines, which, unlike first generation drugs, do not cross into the brain, causing significant drowsiness.
Sleeping Aid
First generation antihistamines are commonly marketed as sleeping pills, notes MayoClinic.com. The most common antihistamine used as a sleeping aid is diphenhydramine. First generation antihistamines cause sleepiness because histamine is a chemical that is produced by the central nervous system. When a person takes a first generation antihistamine, the central nervous system is suppressed, resulting in fatigue. MayoClinic.com warns that these medications are intended for use for a few days to help a person sleep but should not be used on a consistent basis. Trouble sleeping should be discussed with a doctor. Common side effects of these medications are dry mouth, dizziness and memory difficulties.
Antinausea
According to the Encyclopedia of Surgery, some antihistamines are used as an antinausea and motion sickness medication. Drugs.com notes that diphenhydramine is used as an allergy medication, sleeping aid and antinausea (or antiemetic) medication. Most antinausea and motion sickness medications are first generation antihistamines that lead to marked drowsiness. A person taking an antihistamine for nausea and motion sickness should talk to her doctor before using the medication over a long period of time. Nausea may be a sign of a more complicated or severe condition.
