- 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:
Latest Allergies News
Daily Health News
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.
Multimedia: Slideshows, Images & Quizzes
Rosacea, Acne, Shingles, Covid-19 Rashes: Common Adult Skin Diseases
Learn to spot and treat skin conditions commonly found in adults such as acne, Covid-19 rashes, eczema, shingles, psoriasis,...
Sleep Disorders: Insomnia, Sleep Apnea, and More
Learn about the different types of sleep/wake disorders such as insomnia, narcolepsy, and sleep apnea. Explore the symptoms,...
Common Allergies: Symptoms and Signs
What are allergies? Pollen, food, perfumes, and many more things can provoke allergy symptoms. Allergies are an overreaction of...
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?...
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...
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...
Nasal Irrigation: Natural Relief for Cold & Allergy Symptoms
Clogged sinuses and congestion bothering you? Nasal irrigation can relieve sinus symptoms associated with colds and allergies....
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...
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...
Night Shift: Jobs That Can Ruin Your Sleep
Some jobs can lead to sleep problems like insomnia, especially for graveyard and other shift work. Learn how work can disrupt...
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
Nasal allergies are a common problem that affects millions of people. An allergist can recommend the best allergy nasal sprays...
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...
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...
Summer Skin Dangers: Burns, Bites, Stings, and More
Summer can be hazardous to your skin if you come in contact with jellyfish, stingrays, henna tattoos, poison ivy, oak, sumac,...
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...
Related Disease Conditions
Cough: 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 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).
Tonsil stones are small clusters of calcifications that form when food, dead cells, mucus, and bacteria get stuck in the nooks and crannies of the tonsils. Tonsil stones are hard, appear as white or yellowish formations on the tonsils, and usually smell bad due to bacteria. If symptoms occur, they may include persistent bad breath, sore throat, difficulty swallowing, ear pain, and cough.
Hives, 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.
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 skin conditions. The most common of these are scaly patches of skin and red, itchy bumps or patches all over the place.
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 may indicate a problem. Mucus production may increase when allergies, a cold, flu, cough, or sore throat are present. Antihistamines and cold and flu medications may help alleviate excess mucus. A neti pot may be used to decrease nasal congestion and clear mucus.
Nosebleeds are common in dry climates during winter months, and in hot dry climates with low humidity. People taking blood clotting medications, aspirin, or anti-inflammatory medications may be more prone to nosebleeds. Other factors that contribute to nosebleed are trauma (including nose picking, especially in children), rhinitis (both allergic and nonallergic), and high blood pressure. First-aid treatments for a nosebleed generally do not need medical care. Frequent or chronic nosebleeds may require medical treatment such as over-the-counter (OTC) medication, and prevention of nose picking.
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).
Sore throat (throat pain) 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.
The 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.
An 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.
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 needs vary from individual to individual and change throughout your life. The National Institutes of Health recommend about 7-9 hours of sleep each night for older, school-aged children, teens, and most average adults; 10-12 for preschool-aged children; and 16-18 hours for newborns. There are two stages of sleep; 1) REM sleep (rapid-eye movement), and 2) NREM sleep (non-rapid-eye movement). The side effects of lack of sleep or insomnia include: Irritability Tiredness Feeling sleepy during the day Concentration or memory problems Lack of sleep and insomnia can be caused by medical conditions or diseases, medications, stress, or pain. The treatment for lack of sleep and insomnia depends upon the cause.
Panic attacks are sudden feelings of terror that strike without warning. These episodes can occur at any time, even during sleep. A person experiencing a panic attack may believe that he or she is having a heart attack or that death is imminent. The fear and terror that a person experiences during a panic attack are not in proportion to the true situation and may be unrelated to what is happening around them. Most people with panic attacks experience several of the following symptoms: racing heartbeat, faintness, dizziness, numbness or tingling in the hands and fingers, chills, chest pains, difficulty breathing, and a feeling of loss or control. There are several treatments for panic attacks.
Eustachian Tube Dysfunction
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.
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, headache, nausea, vomiting, fatigue, dizziness, cold sweats, and pale skin. Treatment for motion sickness includes home remedies such as ginger, avoiding large or fatty meals prior to traveling, and OTC and prescription medications.
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 symptoms, which symptoms one wishes to relieve, and the active ingredients in the OTC product. Taking products that only contain the medications needed for relieving your symptoms prevents ingestion of unnecessary medications and reduces the chances of side effects.
Lice vs. Fleas
Lice and fleas are small wingless insects. Lice are parasites that can crawl and infest the human skin and scalp. Although they can bite people, fleas are parasites that mainly feed on non-human hosts and can jump from one host to another. Lice infestations and fleabites are treatable and typically do not cause long-term problems with proper treatments for home, people, and pets.
Hay Fever (Allergic Rhinitis)
Hay 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.
Insomnia is the perception or complaint of inadequate or poor-quality sleep because of difficulty falling asleep; waking up frequently during the night with difficulty returning to sleep; waking up too early in the morning; or unrefreshing sleep. Secondary insomnia is the most common type of insomnia. Treatment for insomnia include lifestyle changes, cognitive behavioral therapy, and medication.
Peanut allergies causes signs and symptoms that include hives, itching, redness, and a rash. Severe reactions may cause decreased blood pressure, lightheadedness, difficulty breathing, nausea, and behavioral changes. Someone with a peanut allergy should have an EpiPen with them at all times.
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 symptom and not a disease. The most common causes of insomnia are medications, psychological conditions, environmental changes and stressful events. Treatments may include non-drug treatments, over-the-counter medicines, and/or prescription medications.
What Is Allergic Cascade?
The allergic cascade refers to allergic reactions that happen in the body in response to allergens. A variety of immune cells and chemical messengers participate in the allergic cascade. Symptoms of the allergic cascade range from mild swelling and itching to full-blown anaphylactic shock. Allergen avoidance and medications are used to prevent or treat allergies.
Treatment & Diagnosis
Medications & Supplements
- hydroxyzine (Vistaril)
- diphenhydramine, Benadryl
- fexofenadine and pseudoephedrine (Allegra-D)
- cetirizine (Zyrtec, Zyrtec Allergy, Zyrtec Hives)
- loratadine, Claritin, Claritin RediTabs, Alavert, Claritin Hives Relief, Children's Claritin
- loratadine and pseudoephedrine (Alavert Allergy & Sinus, Claritin-D, Claritin-D 24 hour)
- Cold Medicine and Cough Syrup for Adults
- fexofenadine (Allegra, Mucinex Allergy)
- Side Effects of Phenergan with Codeine (promethazine and codeine)
- desloratadine (Clarinex, Clarinex Reditabs)
Prevention & Wellness
- Antihistamines Linked to Delayed Care for Severe Allergic Reaction: Study
- Aspirin, Antihistamines: Kids Often Use OTC Drugs in Suicide Attempts
- Are Too Many Kids Prescribed Antihistamines?
- Health Tip: Effects of Allergy Medication
- Overdose Attempts Skyrocket Among Teens, Young Adults: Study
- Immune-Targeted Treatment Might Help Prevent Peanut Allergy Crises
- Spring Is the Sneezing Season
- After Peanut Allergy Rx, Eating Small Bits of Peanut Might Help: Study
- Everyday Medications That Can Ruin Your Sex Life
- Health Tip: Understanding Dry Eye
- Health Tip: What Causes Memory Loss?
- Seniors on Multiple Meds a Driving Hazard
- 4 Ways to Protect Your Child From Allergic Reactions at School
- Health Tip: Grapefruit May Interact With Medication
- Antihistamines Adding to Drug Pollution in Streams
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.
U.S. Food and Drug Administration