Antihistamine Ingredients

The Centers for Disease Control and Prevention report as much as 7.6 percent of adults and 16.9 percent of children in the United States suffered from some form of allergy in 2007. Fortunately, the symptoms that accompany allergies are treatable. Antihistamines are the most commonly used drugs to treat allergy disorders. The ingredients that make up these drugs can vary, with each causing a different effect.

Allergic Reactions

• The symptoms most associated with allergies--constant congestion, sneezing, and watery eyes--are the body's way of responding to a perceived threat in the system. Certain individuals have an immune system that's programmed to attack particles like pollen and dust, also known as allergens. When an allergen attaches itself to cells inside the respiratory tract, the immune system reacts by secreting histamines to attack these allergens. In effect, histamine secretions are the cause for the sneezing, congestion and watery eyes. Antihistamines contain ingredients designed to suppress histamine secretions and eliminate allergy symptoms.

Antihistamines

• Antihistamines were first developed in the 1930s, and the formulas created then are still sold as over-the-counter remedies today. These are categorized as first generation antihistamines. The main active ingredient in first generation formulas is diphenhydramine, which is effective in treating allergy symptoms, but there is a high potential for side effects. Drowsiness, agitation, insomnia, dizziness and dry mouth are all known side effects of taking antihistamine medications. Histamine sites reside in the respiratory tract and in the brain. Diphenhydramine acts on histamine sites in both areas, which accounts for the side effects experienced from these drugs.

Nondrowsy Formulas

• Second and third generation antihistamines were developed in the 1980s in an attempt to eliminate the side effects caused by the first generation formulas. These are labeled as the "nondrowsy formulas." The active ingredients are pain relievers and decongestants, and some brands may contain varying amounts of antihistamine agents. They come in both regular and extended-release formulas, but most brands are available only by prescription. Possible side effects associated with regular-release formulas include drowsiness, dry mouth, headache and dry nose. Possible side effects associated with extended-release formulas include insomnia, restlessness, and nervousness.

Anticholinergics

• Anticholinergics are medications that prevent acetylcholine from being secreted by receptor sites located in the brain and all throughout the body. Acetylcholine is an essential brain neurotransmitter that's involved with sending messages between the motor nerves and muscles. First generation antihistamines contain anticholinergic agents that make them so effective at treating allergy symptoms. Brompheniramine maleate, chlorcyclizine hydrochloride, chlorpheniramine maleate and dexbrompheniramine maleate are some of the anticholinergic ingredients found in over-the-counter antihistamine medications.

Brand Types

• Antihistamines which contain anticholinergic ingredients include Dimetapp Cold & Allergy Elixir, Robitussin Allergy & Cough Liquid, Vicks NyQuil, and Benadryl Allergy. Nondrowsy formula medications requiring a prescription include Clarinex, Claritin D, and Allegra. Prescription-only formulas are more effective at treating symptoms, but they are also more expensive than over-the-counter remedies. Over-the-counter nondrowsy medications include Claritin and Zyrtec. Claritin and Zyrtec are classified as second generation antihistamines, but both contain a combination of antihistamine and decongestant ingredients. Over-the-counter decongestant medications used to treat allergy symptoms include Dimetapp, Robitussin and Sudafed.