- 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
Quick GuideBad Bugs: Identify Bug Bites From Mosquitos, Spiders and More
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.
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...
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....
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...
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...
Allergies Quiz: Symptoms & Home Remedies
What are the causes of allergies? This online quiz challenges your knowledge of common food and household allergens,...
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?...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
Sore throat usually is described as pain or discomfort in the throat area. A sore throat may be caused by bacterial...
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...
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...
Vulvodynia (Vaginal Pain)
Vulvodynia or vaginal pain, genital pain is a condition in which women have chronic vulvar pain with no known cause. There are...
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 sickness,...
Hay Fever (Allergic Rhinitis)
Hay fever (allergic rhinitis) is an irritation of the nose caused by pollen and is associated with the following allergic...
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...
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...
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...
Panic attacks are sudden feelings of terror that strike without warning. These episodes can occur at any time, even during sleep....
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...
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
- Allergies FAQs
- Sleep FAQs
- Summer Skin Hazards Pictures FAQs
- Skin FAQs
- Drugs: The Most Common Medication Errors
- Medication Disposal - What to Do with Old or Unusable Medication
- Dangers of Mixing Medications
- Generic Drugs, Are They as Good as Brand-Names?
- Drugs: Buying Prescription Drugs Online Safely
Medications & Supplements
- hydroxyzine (Vistaril)
- diphenhydramine, Benadryl
- loratadine, Claritin, Claritin RediTabs, Alavert, Claritin Hives Relief, Children's Claritin
- cetirizine, Zyrtec, Zyrtec Allergy, Zyrtec Hives
- fexofenadine, Allegra, Allegra Allergy, Allegra Hives, Children's Allegra, Mucinex Allergy
- loratadine and pseudoephedrine (Alavert Allergy & Sinus, Claritin-D, Claritin-D 24 hour)
- fexofenadine and pseudoephedrine, Allegra-D
- desloratadine, Clarinex, Clarinex Reditabs
Prevention & Wellness
Daily Health News
Subscribe to MedicineNet's Allergy and Asthma Newsletter
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.
Top antihistamines-oral Related Articles
Know Your Allergy TriggersAllergies are an overreaction of the immune system where the body's defenses react to substances such as pollen, food and more. Learn about common allergy triggers and how you can avoid an allergy attack.
Take the Allergies QuizWhat are the causes of allergies? This online quiz challenges your knowledge of common food and household allergens, environmental triggers, allergic diseases and conditions, and allergy symptoms and treatments.
AllergyAn allergy refers to a misguided reaction by our immune system in response to bodily contact with certain foreign substances. When these allergens come in contact with the body, it causes the immune system to develop an allergic reaction in people who are allergic to it. It is estimated that 50 million North Americans are affected by allergic conditions. The parts of the body that are prone to react to allergies include the eyes, nose, lungs, skin, and stomach. Common allergic disorders include hay fever, asthma, allergic eyes, allergic eczema, hives, and allergic shock.
Common ColdThe common cold (viral upper respiratory tract infection) is a contagious illness that may be caused by various viruses. Symptoms include a stuffy nose, headache, cough, sore throat, and maybe a fever. Antibiotics have no effect upon the common cold, and there is no evidence that zinc and vitamin C are effective treatments.
Eustachian Tube Problems
The Eustachian tube is a membrane lined tube that connects the middle ear space to the back of the nose. Symptoms of Eustachian tube dysfunction or blockage include popping and/or clicking in the ear, and ear fullness and/or pain.
Causes of Eustachian tube dysfunction or blockage include allergies, sinus infections, ear infections, and the common cold.
Treatment includes home remedies to relieve pain and several maneuvers (swallowing, chewing gum, yawning etc.), which can be done to improve Eustachian tube function. In severe cases surgery may be necessary.
Eye Allergies PictureSevere allergic eye symptoms can be very distressing and are a common reason for visits to the allergist or ophthalmologist. See a picture of Eye Allergies and learn more about the health topic.
Hay FeverHay fever (allergic rhinitis) is an irritation of the nose caused by pollen and is associated with the following allergic symptoms: nasal congestion, runny nose, sneezing, eye and nose itching, and tearing eyes. Avoidance of known allergens is the recommended treatment, but if this is not possible, antihistamines, decongestants, and nasal sprays may help alleviate symptoms.
HivesHives, also called urticaria, is a raised, itchy area of skin that is usually a sign of an allergic reaction. The allergy may be to food or medications, but usually the cause of the allergy (the allergen) is unknown.
How to Stop Coughing
Coughing is a reflex that helps a person clear their airways of irritants. There are many causes of an excessive or severe cough including irritants like cigarette and secondhand smoke, pollution, air fresheners, medications like beta blockers and ACE inhibitors, the common cold, GERD, lung cancer, and heart disease.
Natural and home remedies to help cure and soothe a cough include stay hydrated, gargle saltwater, use cough drops or lozenges, use herbs and supplements like ginger, mint, licorice, and slippery elm, and don't smoke.
Over-the-counter products (OTC)to cure and soothe a cough include cough suppressants and expectorants, and anti-reflux drugs.
Prescription drugs that help cure a cough include narcotic medications, antibiotics, inhaled steroids, and anti-reflux drugs like proton pump inhibitors or PPIs, for example, omeprazole (Prilosec), rabeprazole (Aciphex), and pantoprazole (Protonix).
Motion Sickness (Sea Sickness, Car Sickness)Motion sickness is a feeling of unwellness caused by the inner ear and balance systems. Motion sickness can include sea sickness, car sickness, and train or plane sickness. Symptoms include:
- cold sweats, and
- pale skin.
RashThe word "rash" means an outbreak of red bumps on the body. The way people use this term, "a rash" can refer to many different skin conditions. The most common of these are scaly patches of skin and red, itchy bumps or patches all over the place.
Sex-Drive KillersNoticing a lack of intimacy with your partner? Here we explore how stress, lack of sleep, weight gain, depression and low T can cause low sex drive in men and women.
Skin Problems SlideshowLearn to spot and treat skin conditions commonly found in adults such as acne, eczema, shingles, psoriasis, rosacea, hives, cold sores, razor bumps, athlete's foot, and more.
Take the Skin QuizWhat's that all over you? Skin, of course! Test your knowledge of your most amazing organ with the Skin Quiz!
Sleep DisordersLearn about the different types of sleep disorders such as insomnia and sleep apnea. Explore the symptoms, causes, tests and treatments of sleep disorders.
Take the Sleep QuizTake our Sleeping Quiz to learn which sleep disorders, causes, and symptoms rule the night. Trouble falling or staying asleep? Find out which medical treatments fight sleep deprivation, apnea, insomnia, and more!
Sore Throat (Pharyngitis)
Sore throat usually is described as pain or discomfort in the throat area. A sore throat may be caused by bacterial infections, viral infections, toxins, irritants, trauma, or injury to the throat area. Common symptoms of a sore throat include a fever, cough, runny nose, hoarseness, earaches, sneezing, and body aches. Home remedies for a sore throat include warm soothing liquids and throat lozenges. OTC remedies for a sore throat include OTC pain relievers such as ibuprofen or acetaminophen. Antibiotics may be necessary for some cases of sore throat.
Vaginal Pain (Vulvodynia)
Vulvodynia or vaginal pain, genital pain is a condition in which women have chronic vulvar pain with no known cause. There are two types of vulvodynia, generalized vulvodynia and vulvar vestibulitis. Researchers are trying to find the causes of vulvodynia, for example, nerve irritation, genetic factors, hypersensitivity to yeast infections, muscle spasms, and hormonal changes.The most common symptoms of vaginal pain (vulvodynia) is burning, rawness, itching, stinging, aching, soreness, and throbbing. There are a variety of treatments that can ease the symptoms of vulvodynia (vaginal pain).