According to the University of Iowa, antihistamines are commonly used to treat allergy symptoms, as a sleeping aid and to suppress nausea and vomiting. Antihistamines are sold over the counter and are available with a doctor's prescription. They are best known for their ability to prevent and treat allergic reaction symptoms such as a runny nose, nasal congestion, irritated eyes and hives. Before taking any medication, talk with a doctor.
Types--Sedating
Sedating antihistamines, or first generation antihistamines, are known for their ability to sedate the user, according to Net Doctor. Sedating antihistamines are older drugs that are commonly taken every four to six hours, according to FamilyDoctor.org. The most common OTC sedating antihistamines are diphenhydramine, dimehydrinate, chlorpheniramine, doxylamine and brompheniramine. These drugs are primarily marketed for allergy relief, and some are used for motion sickness or as a sleeping aid.
Types--Nonsedating
Nonsedating, or second generation, antihistamines are newer drugs that are taken in single, 24-hour doses and do not cause drowsiness in healthy adults, according to FamilyDoctor.org. Nonsedating antihistamines do not suppress the central nervous system, so they are not used to treat nausea or motion sickness. Two nonsedating antihistamines are available OTC: loratadine and cetirizine.
Allergen Function
According to the American Academy of Otolaryngology, antihistamines primary function is to block histamine, a chemical in the body that causes allergy symptoms. When an allergen enters a person's body the immune system tries to fight it off by releasing antibodies. Antibodies cause the cells in the body to produce histamines as a defense system. Histamine in turn causes harm to surrounding cells and affects mucus-producing membranes, according to Net Doctor.
Other Functions
Antihistamines are also used as a sleeping aid and treatment for nausea and vomiting, according to the University of Iowa. Sedating antihistamines work by suppressing the central nervous system, causing marked drowsiness. Nausea is not controlled by the stomach, but is a reaction in the brain. The suppression of the central nervous system causes the feeling of nausea to subside, which relieves the urge to vomit.
Considerations
Antihistamines should not be taken with alcohol, sleeping pills, sedatives or muscle relaxants, according to FamilyDoctor.org. People with thyroid disease, asthma, glaucoma, high blood pressure, heart disease or an enlarged prostate should not take antihistamines. Talk with a doctor before taking any medication and disclose family history and any health concerns.
