- 10 Common Allergy Triggers Slideshow Pictures
- Take the Quiz on Allergies
- Nasal Allergy Relief Products Slideshow
- What are oral antihistamines?
- What are examples of oral antihistamines available in the US?
- What are the side effects of oral antihistamines?
- What drugs interact with oral antihistamines?
- What formulations of oral antihistamines are available?
- What about taking oral antihistamines during pregnancy or while breastfeeding?
What are oral antihistamines?
The term, antihistamine generally is used for medications used to treat various symptoms believed to be caused by histamine, for example, as part of the common cold, including:
(A second type of antihistamine is used primarily for suppressing acid production in the stomach and treating acid-related diseases such as ulcers of the stomach. 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. Antihistamines also can be used on an as needed basis for those who experience occasional symptoms or symptoms triggered by exposure to certain irritants such as animal hair, plants, medications, and food products. Some antihistamines also may be used occasionally to help with sleep.
Many different brands and forms of oral antihistamines are available over the counter (OTC). Oral antihistamines are available as pills, chewable tablets, orally disintegrating tablets, capsules, and liquid. 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.
Antihistamines are divided into two categories, first generation or older agents and second generation or newer agents. First generation antihistamines have many drawbacks including side effects of drowsiness and significant anticholinergic side effects that, for example, can cause difficulty urinating or constipation, and are therefore not used very often. The newer antihistamines (second generation) are less likely to cause these side effects.
Antihistamines also differ in how long they work. Long-acting antihistamines provide symptom relief for up to 8-12 hours, while shorter acting agents last for up to 4 hours but begin working faster.
What are examples of oral antihistamines available in the US?
First generation antihistamines include
- chlorpheniramine (Chlor-Trimeton)
- diphenhydramine (Benadryl)
- doxylamine (found in many OTC sleep aids including Unisom)
- carbinoxamine (Karbinal ER)
Second generation antihistamines include
What are the side effects of oral antihistamines?
First generation antihistamines are used less often to treat allergies because they cause significant sedation. First generation antihistamines also should be used cautiously in older adults as they are more susceptible to their anticholingeric side effects including
- dry mouth,
- decreased tear production,
- urinary retention (trouble urinating),
- blurred vision,
- constipation, and
Due to their significant side effect profile, special precautions should be used in patients with:
- Problems passing urine or men with prostate problems
- Thyroid disorders
- High blood pressure
Second generation antihistamines are less sedating than their first generation counterparts. Cetirizine can be sedating for some patients at normal recommended doses while sedation seems to only be a concern with loratadine at higher than normally recommended doses. Fexofenadine is the least sedating.
Side effects common to all antihistamines include:
What drugs interact with oral antihistamines?
Antihistamines may cause drowsiness. Taking antihistamines with other medicines that also are sedating may cause profound drowsiness. Examples include:
- Sleeping pills
- Seizure medications
- Some antidepressants (especially tricyclic antidepressants)
- Muscle relaxants
- Prescription narcotic pain medications
- Other antihistamines
- MAOIs (monoamine oxidase inhibitors), a class of medications used to treat mood disorders, may prolong or intensify the anticholinergic side effects of antihistamines. Generally, first generation antihistamines should not be used within two weeks of using a MAOI.
What formulations of oral antihistamines are available?
- Chewable tablets
- Orally disintegrating tablets
- In-combination with decongestants and pain relievers
What about taking oral antihistamines during pregnancy or while breastfeeding?
Non-drug interventions should always be considered first in pregnant women suffering from symptoms of allergic rhinitis. Nondrug therapies include saline or salt-water nasal sprays, exercise, and nasal strips.
If a daily antihistamine is needed during pregnancy, second generation agents are preferred because they are less sedating and have a better side effect profile (have fewer anticholingeric side effects). Loratadine and cetirizine are preferred second generation antihistamines for pregnant women because they have the most safety and efficacy data. Both agents are rated FDA category B, and are generally considered to be safe at recommended doses for the treatment of allergic rhinitis during pregnancy. Fexofenadine is less well-studied and is rated FDA pregnancy category C.
First generation antihistamines are usually used on an as-needed basis or before bedtime to occasionally help with sleep. Chlorpheniramine is the preferred first generation antihistamine for people who are pregnant because it has been studied the most.
Quick GuideBad Bugs: Identify Bug Bites From Mosquitos, Spiders and More
Oral antihistamines are medications used to treat symptoms of congestion, runny nose, the common cold, sneezing, itchy throat, skin rashes, hives, itching, and watery or itchy eyes. Some antihistamines also are used to treat anxiety, insomnia, and motion sickness. Side effects, drug interactions, dosing, storage, and pregnancy and breastfeeding safety information should be reviewed prior to taking this class of medication.
Multimedia: Slideshows, Images & Quizzes
Rosacea, Acne, Shingles: Common Adult Skin Diseases
Learn to spot and treat skin conditions commonly found in adults such as acne, eczema, shingles, psoriasis, rosacea, hives, cold...
Allergies Quiz: Symptoms & Home Remedies
What are the causes of allergies? This online quiz challenges your knowledge of common food and household allergens,...
Summer Skin Risks: Sunburn, Bug Bites & Poison Ivy
When it comes to summer, there plenty of hazards under the sun! Take the Summer Skin Hazards Quiz and clue in on the dangers to...
Skin Quiz: Acne, Dry Skin, Dandruff & More
What's that all over you? Skin, of course! Test your knowledge of your most amazing organ with the Skin Quiz!...
Sleep Quiz: Sleep Hygiene & Sleep Facts
Take our Sleeping Quiz to learn which sleep disorders, causes, and symptoms rule the night. Trouble falling or staying asleep?...
Picture of Eye Allergies
Severe allergic eye symptoms can be very distressing and are a common reason for visits to the allergist or ophthalmologist. See...
Could I Be Allergic? Discover Your Allergy Triggers
Allergies are an overreaction of the immune system where the body's defenses react to substances such as pollen, food and more....
Sleep Disorders: Insomnia, Sleep Apnea, and More
Learn about the different types of sleep disorders such as insomnia and sleep apnea. Explore the symptoms, causes, tests and...
Sex-Drive Killers: The Causes of Low Libido
Noticing a lack of intimacy with your partner? Here we explore how stress, lack of sleep, weight gain, depression and low T can...
Nasal Irrigation: Natural Relief for Cold & Allergy Symptoms
Nasal irrigation can relieve sinus symptoms associated with colds & allergies. Learn how nasal irrigation can help unclog sinuses...
Pictures of Allergy Relief Tips at Home: AC Filters, Electronic Air Cleaners, and More
Learn how a combination of medication, preventing allergens, and allergy relief products can reduce allergy symptoms and help you...
Out-of-Control Allergy Symptoms: Treatment Relief in Pictures
Learn 10 signs your allergies are out of control. See these surprising allergy symptoms and find out how to get relief for...
Summer Skin-Hazard Pictures: Stings, Bites, Burns, and More
Don't let spider bites, sunburn, poison ivy, chigger bites, and jellyfish stings sabotage your healthy skin. Learn how you can...
Jobs That May Ruin Your Sleep
Some jobs can lead to sleep problems like insomnia, especially for graveyard and other shift work. Learn how work can disrupt...
20 Tips to Beat Insomnia and Sleep Better
Good sleep hygiene leads to better sleep. Avoid insomnia and sleep better by minimizing stress, exercising, and taking proper...
Home Allergy Quiz: Is Your Home Allergy-Proof?
Take this home allergy quiz and test your knowledge on allergens, dust mites, pollens and more to see how allergy-proof your home...
When Animal (Allergies) Attack: Pet Allergy Symptoms, Treatment
How do you control and relieve pet allergies? How do you prevent pet allergies? Learn dog and cat allergy symptoms, the cause of...
Nasal Allergy Attack: Causes, Triggers, Treatments
What causes allergies? What are your allergy triggers? Discover how allergies work, why our bodies react to them, whether...
10 Worst Cities for Spring Allergies With Pictures
See pictures of the top 10 "spring allergy capitals", according to the Asthma and Allergy Foundation of America (AAFA). From...
The Most Common Food Allergies for Kids and Adults
What common food allergens cause the most problems for adults and children? See this list of common food allergies and learn to...
Related Disease Conditions
The word "rash" means an outbreak of red bumps on the body. The way people use this term, "a rash" can refer to many different...
Eustachian Tube Problems (Ear Tube Dysfunction, Blockage)
The Eustachian tube is a membrane lined tube that connects the middle ear space to the back of the nose. Symptoms of Eustachian...
19 Tips on How to Stop a Cough
Coughing is a reflex that helps a person clear their airways of irritants. There are many causes of an excessive or severe...
Nosebleeds are common in dry climates during winter months, and in hot dry climates with low humidity. People taking blood...
Vulvodynia or vaginal pain, genital pain is a condition in which women have chronic vulvar pain with no known cause. There are...
Hives (Urticaria & Angioedema)
Hives, also called urticaria, is a raised, itchy area of skin that is usually a sign of an allergic reaction. The allergy may be...
What Is Mucus?
Mucus is a normal substance produced by lining tissues in the body. Excess mucus or mucus that is yellow, green, brown, or bloody...
Sore throat (throat pain) usually is described as pain or discomfort in the throat area. A sore throat may be caused...
The common cold (viral upper respiratory tract infection) is a contagious illness that may be caused by various viruses. Symptoms...
Motion sickness is a feeling of unwellness caused by the inner ear and balance systems. Motion sickness can include sea...
An allergy refers to a misguided reaction by our immune system in response to bodily contact with certain foreign substances. ...
Sleep Disorders (How to Get a Good Night's Sleep)
A number of vital tasks carried out during sleep help maintain good health and enable people to function at their best. Sleep...
Hay Fever (Allergic Rhinitis)
Hay fever (allergic rhinitis) is an irritation of the nose caused by pollen and is associated with the following allergic...
Insomnia (Symptoms, Causes, Remedies, and Cures)
Insomnia is the perception or complaint of inadequate or poor-quality sleep because of difficulty falling asleep; waking up...
Panic attacks are sudden feelings of terror that strike without warning. These episodes can occur at any time, even during sleep....
Cold, Flu, Allergy Treatments
Before treating a cold, the flu, or allergies with over-the-counter (OTC) medications, it's important to know what's causing the...
Insomnia Treatment (Sleep Aids and Stimulants)
Insomnia is difficulty in falling or staying asleep, the absence of restful sleep, or poor quality of sleep. Insomnia is a...
The allergic cascade refers to allergic reactions that happen in the body in response to allergens. A variety of immune cells and...
Treatment & Diagnosis
Medications & Supplements
- hydroxyzine (Vistaril)
- diphenhydramine, Benadryl
- fexofenadine, Allegra, Allegra Allergy, Allegra Hives, Children's Allegra, Mucinex Allergy
- cetirizine, Zyrtec, Zyrtec Allergy, Zyrtec Hives
- loratadine and pseudoephedrine (Alavert Allergy & Sinus, Claritin-D, Claritin-D 24 hour)
- loratadine, Claritin, Claritin RediTabs, Alavert, Claritin Hives Relief, Children's Claritin
- fexofenadine and pseudoephedrine, Allegra-D
- desloratadine, Clarinex, Clarinex Reditabs
Prevention & Wellness
Health Solutions From Our Sponsors
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.