Bay Area Medical Information
Antihistamines
Antihistamines help relieve allergy symptoms

Sneezing, coughing, watery eyes, runny nose, an itchy rash, or hives can all be symptoms of an allergic reaction. Allergy treatment usually starts with avoiding the substances (allergens) that cause the allergic symptoms but sometimes this is not possible and medication is necessary to help relieve symptoms. Allergy medication is available in pill, liquid, nasal spray, eyedrop and topical (applied to the skin) forms. Some allergy medications are over-the-counter and others are by prescription only. To find out what's best for you, get advice from your doctor.

Antihistamines usually cause severe drowsiness which can be a helpful side effect if sleep is needed. (A newer drug, loratadine is an exception and usually does not cause drowsiness.) Antihistamines are usually the main active ingredient in over-the-counter sleep aides, such as Tylenol PM. In general, as a sleep aid, antihistamines are not ideal. In many people, especially the elderly, they often last longer than needed for a good night's sleep and thus result in drowsiness that might last till noon the next day. Another disadvantage is that the side effect of drowsiness does wear off with continuous use. It's important to note that the individual response each of these medicines varies from person to person.

Oral antihistamines are often one of the active ingredients in cold preparations.

Motion Sickness: Some of the antihistamines are also used to prevent motion sickness, nausea, vomiting, and dizziness.

Examples of common antihistamines: There are a number of antihistamines available only by prescription but there also many effective antihistamines that you might see on a label in the grocery store or pharmacy:

  • brompheniramine maleate (Dimetapp)
  • loratadine (Alavert, Claritin)--not supposed to cause drowsiness, but this response can vary in different people
  • diphenhydramine HCl (Benadryl Allergy, Tylenol PM)
  • chlorpheniramine maleate (Chlor-trimeton)
  • clemastine (Tavist Allergy)

It's very important to read the label before using these products. Elderly should be particularly cautious in using antihistamines, especially on a regular basis.

  • An important consideration about the use of antihistamines is that sudden urinary retention is a significant problem than can occur in susceptible individuals, particularly men over 50 who have an enlarged prostate.

  • The following precautions usually apply to this category of medication: Asthma and lower respiratory disorders, glaucoma, hyperthyroidism, hypertension, cardiovascular disease, GI obstruction, urinary obstruction, children, pregnancy. Diphenhydramine interacts with: alcohol and other CNS depressants as well as MAOIs.

  • You shouldn't take prescription antihistamines if you are taking certain other prescription drugs -- ask your doctor or pharmacist if the medication will interact.

  • For a comprehensive list of contraindications, precautions, and side effects of antihistamines click here

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