How to Know When to Take Antihistamines

Three Parts:Understanding AntihistaminesChoosing an Antihistamine For Your SymptomsTaking Preventive Steps

Antihistamines work by blocking histamine, a substance produced by your cells to prevent infection.[1] If your body detects a foreign substance, your cells will make histamine, which causes inflammation of blood vessels. Usually this is useful. But when your body mistakes a non-harmful substance, like pollen, for a harmful one, it can cause what we call seasonal allergies.[2] Antihistamines are commonly known for treating seasonal allergies, but there are several other uses for both over-the-counter antihistamines and those prescribed by a doctor. Before taking antihistamines, understand how antihistamines work and what symptoms they treat.

Part 1
Understanding Antihistamines

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    Know the common side effects. Common side effects include drowsiness, dizziness, dry mouth, feelings of excitement or nervousness, decreased appetite, abdominal pain, constipation, and blurry vision.[3][4]
    • Side effects, particularly drowsiness, are more pronounced with “first generation” antihistamines such as chlorpheniramine, diphenhydramine, promethazine, and hydroxyzine. The most common over-the-counter first generation antihistamine is diphenhydramine, the active ingredient in Benadryl.
    • Second and third generation antihistamines generally have fewer side effects. Second generation antihistamines include cetirizine (Zyrtec) and loratadine (Claritin). Third generation antihistamines include desloratadine (Clarinex) and fexofenadine (Allegra). These medications cause less drowsiness than other antihistamines.[5][6]
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    Be aware of interactions. Antihistamines may cause reaction with other medications or substances. For example, you should avoid alcohol when taking antihistamines. Antihistamines can also interact with muscle relaxants (such as carisoprodol and cyclobenzaprine), sleeping pills (such as zolpidem), and sedatives (such as benzodiazepines) so avoid taking antihistamines with these medications.[7]
    • If you have glaucoma, overactive bladder or trouble urinating, respiratory issues such as asthma, heart issues or high blood pressure, kidney or liver issues, or thyroid disease, make sure to ask your doctor before taking antihistamines.[8]
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    Choose between over-the-counter (OTC) and prescription antihistamines. Try taking over the counter antihistamines if you have predictable, intermittent, short-term (few weeks) mild to moderate symptoms of an allergy such as sneezing, itchy, watery eyes or runny nose, or mild hives. If these don't work or you experience side effects, prescription medications may be a better option.[9]
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    Correctly take antihistamines. Follow the directions on the label for the particular medication you are taking. Most of the oral antihistamines should be taken everyday during the time you are experiencing allergy symptoms. If allergies are severe, uncontrolled by the medication, last longer than the common allergy season, or chronic contact your doctor.[10]
    • If you are elderly, have other health conditions, are taking medications or supplements or treating a child for allergies contact a doctor before taking an over the counter antihistamine. Your doctor may determine that other medications or treatments may be a better option for you.
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    Choose a child-strength antihistamine for children. Several antihistamines are available in child-strength formulations. Your pediatrician or pharmacist can advise you which is right for your child. Never give a young child adult-strength antihistamines.[11]
    • Children’s antihistamine is available in caplets, syrups, chewables, and melt-away tabs for easy dosing.
    • Follow the directions on the label. Generally, child-strength antihistamines are approved for use in children 2 and older. Some are approved for as young as 6 months. Consult your pediatrician if your child is younger than 2.[12][13]
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    Know when to go to the doctor. Once you've started taking antihistamines, talk to your doctor if your symptoms are severe or get worse. You should also call your doctor if you develop a nosebleed or other nasal symptoms. Tell your doctor if the symptoms don't lessen or go away. Common symptoms include:[14]
    • Dizziness
    • Dry mouth
    • Feeling irritable, jittery, or excited
    • Changes in vision, including blurred vision
    • Loss of appetite
    • If you start having shortness of breath or trouble breathing, contact emergency services right away. You may be having an anaphylactic reaction.
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    Recognize emergency symptoms in children. Children are particularly prone to medication overdose. If you notice any of the following symptoms after giving your child antihistamines, call the Poison Help line at 1-800-222-1222[15] and seek emergency medical attention for your child:[16][17][18]
    • Extreme drowsiness
    • Confusion
    • Agitation
    • Muscle weakness
    • Convulsions
    • Hallucination

Part 2
Choosing an Antihistamine For Your Symptoms

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    Take an oral antihistamine for allergy symptoms like sneezing, itchy and watery eyes, or runny nose. If you have allergic rhinitis or hay fever, you can take first or second generation antihistamines. First generation antihistamines, like diphenhydramine (Benadryl) or chlorpheniramine, can cause drowsiness and other side effects. These are available over the counter. Second or third generation antihistamines may be a better option for ongoing symptoms of hay fever.
    • Second and third generation antihistamines usually require only once or twice daily dosing, which is easier to comply with.
    • Second generation antihistamines like cetirizine (Zyrtec), fexofenadine (Allegra), or loratadine (Claritin) cause significantly less drowsiness and fewer other side effects.
    • Prescription third-generation antihistamines include desloratadine (Clarinex) and levocetirizine dihydrochloride (Xyzal) and may be a better option if you have side effects with over the counter antihistamines.
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    Use an antihistamine nasal spray for symptoms such as itchy or runny nose, sneezing, sinus congestion or postnasal drip. Antihistamine nasal sprays are used to directly treat cold and allergy-related nasal symptoms. These are available by prescription and include azelastine (Astelin, Astepro) and olopatadine (Patanase).[19]
    • Side effect of these antihistamines slightly differ from the oral ones and include bitter taste, fatigue and weight gain, burning sensation in nostrils, and possible drowsiness.[20] Use as directed by your doctor.
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    Consider antihistamine eye drops to relieve itchy, watery red eyes. You can get them over the counter or as a prescription. For example, you could try azelastine (Optivar) or olopatadine (Pataday, Patanol) by prescription. Or, try ketotifen (Alaway, Zaditor) or pheniramine (Visine-A, Opcon-A) over the counter.[21] Side effects can include headache, burning sensation and dry eyes.
    • To insert eye drops properly, wash your hands with soap and warm water. Next, remove your contact lenses, tilt your head back, look up and pull down the lower eyelid. Apply the prescribed number of drops. Keep your eyes closed for 1 to 2 minutes. Place one finger at the inside corner of your eye and apply gentle pressure. This will prevent the medication from draining out. Wait 10 minutes before reinserting your contacts.
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    Use a cold medication with an antihistamine for symptoms such as congestion, sneezing and runny nose associated with the cold.[22] The antihistamine in cold medications may help symptoms associated with your cold and improve recovery,[23] although they are more effective for older children and adults, and not all studies show a significant benefit.[24] Many cold medications offer an antihistamine and decongestant combination.
    • Take the medication with a glass of water. Do not crush or chew the tablets.[25]
    • Examples include fexofenadine and pseudoephedrine (Allegra-D) or loratadine and pseudoephedrine (Claritin-D). Both are available as a 12 or 24 hour treatment taken twice or once a day respectively.
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    Try an antihistamine for a dry cough. If you have a dry cough, an antihistamine can be a good first option to treat it.[26] Most antihistamines are effective to treat cough.[27]
    • Try diphenhydramine (Benadryl) at night or something like cetirizine (Zyrtec) or fexofenadine (Allegra), which don’t cause as much drowsiness, during the day.
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    Find an antihistamine to prevent nausea, dizziness or vomiting associated with motion sickness. Certain OTC antihistamines sold can be used to treat nausea and vomiting associated with motion sickness. Many products act on the part of the brain that prevents nausea, which is why some people take antihistamines before traveling on an airplane or by boat. You should usually take them one hour before the activity or departure.
    • Long-lasting, low drowsy options include: dimenhydrinate (Dramamine, Gravol, Driminate), meclizine (Bonine, Bonamine, Antivert, Postafen, and Sea Legs), and cyclizine (Marezine, Bonine For Kids, Cyclivert). Promethazine (Phenergan) is prescribed for treating nausea or vomiting, motion sickness, and allergic reactions, but can cause more drowsiness.[28]
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    Take an oral antihistamine for itchy rashes or hives. Rashes and hives may be caused by the production of too much histamine, and second or third generation antihistamines can help block your body’s release of histamine.[29] Talk with your doctor about taking one of the following daily:
    • Cetirizine (Zyrtec)
    • Fexofenadine (Allegra)
    • Loratadine (Claritin, Alavert)
    • Levocetirizine (Xyzal)
    • Desloratadine (Clarinex)
    • If the newer-generation antihistamines do not appear to work, your doctor may recommend that you take a first generation antihistamine such as diphenhydramine (Benadryl). Take these before bed each night, as they cause drowsiness.
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    Apply a topical antihistamine if you have itching or a rash from bug bites or inflammation. Topical antihistamines come in lotion or cream form and can be applied directly to the affected area as needed, up to 4 times a day. They usually contain diphenhydramine, often in combination with a skin protectant like calamine.[30] If you develop pain, redness, swelling, hives, or difficulty breathing after an insect bite, contact emergency services right away. These are signs that you are having an allergic reaction to the bite.[31]
    • If you have pus, swelling, or if your rash gets bigger, changes color, or does not go away in a couple days contact your doctor. This may be a sign of a different skin condition or infection that may need prescription medication.
    • Don't use topical antihistamines with oral antihistamines which can increase the concentration of antihistamine in your body. Make sure not to apply topical antihistamines to a very large area of your skin or skin that is broken or blistered.[32]
    • If you have insect bites or a rash over a large area of your body, try an oral antihistamine instead. Contact your doctor if your bites or rash is very severe.
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    Look for an antihistamine that can cause drowsiness if you have trouble sleeping. Some over the counter antihistamine products are marketed as sleeping aids because of the side effect of drowsiness. But, you can develop tolerance to the drowsiness caused by antihistamines. So the more or longer you use them, the less effective they will be. Be aware that they can also cause drowsiness and grogginess the next day.[33]
    • Options include diphenhydramine (Benadryl, Unisom SleepGels) or doxylamine succinate (Unisom SleepTabs).
    • Only take drowsiness-inducing antihistamines before you go to bed. Do not drive or operate machinery after taking drowsiness-inducing antihistamines.
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    Discuss using antihistamines to help with anxiety with your doctor. Some antihistamines may help with anxiety because they can cause sedation. The most common antihistamine prescribed for anxiety or preoperative sedation is hydroxyzine.
    • This is usually given as 50-100 mg by mouth every 6 hours. Side effects include dry mouth, drowsiness and tremors.[34]
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    Ask your doctor about antihistamine use for Parkinson's. Antihistamines may help with abnormal movements in patients with Parkinson's. Diphenhydramine can sometimes be used since it blocks the neurotransmitters. This helps control abnormal movements associated with early stage Parkinson’s or as a side effect of medication.[35]

Part 3
Taking Preventive Steps

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    Avoid allergens. Avoid things that you have noticed trigger allergies. Common allergy triggers include certain foods, dust, insect bites, pet dander, drugs, latex, mold, and cockroaches.[36]
    • When you eat out, tell your server about any food allergies you have. Restaurants usually have strict policies in place to help avoid allergic reactions.
    • Stay indoors between 5AM to 10AM if you have pollen allergies. Pollen counts are usually highest during these hours.[37]
    • Wear a face mask and eye protection if you do yardwork. Shower immediately afterward to remove any dust or pollen.
    • Apply insect repellant when you go outside to avoid insect bites.
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    Manage allergens in your home. It’s more difficult to avoid allergens out in public, but there are several things you can do to make your home more allergy-friendly.[38][39]
    • Dust and vacuum regularly. Get a vacuum with a HEPA filter to filter out minute allergy-causing particles.
    • Cover your pillows and mattresses with dust mite covers. You can buy these online or at many home or department stores.
    • Look for cleaning products, such as Febreze Allergen Reducer, that you can use on things such as upholstery, carpet, and curtains.
    • Never smoke inside your home.
    • Use antibacterial cleaners for your kitchen and bathroom. Ventilate your kitchen and bathroom by running vent hoods and fans to avoid mold growth.
    • Bathe pets once a week to reduce dander. If you have bad pet allergies, don’t sleep with your pet.
    • Wash bedding in hot water every week or two. This will help kill dust mites.[40]
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    See an allergist for an allergy test. If you have reduced allergens in your home and used antihistamines and you’re still not seeing relief, see an allergist and ask for an allergy test. These tests allow your allergist and physician to determine your precise allergies and come up with a treatment plan for you.[41]
    • You may experience an allergic reaction to some tests. It’s important to have an allergy specialist perform any allergy test. The American College of Allergy, Asthma & Immunology has a “Find an Allergist” feature on their website.[42]
    • Allergy tests can be done as either skin tests or blood tests. Skin tests are fast and allow many allergens to be tested at the same time. Blood tests are often used if you have a severe skin condition or are likely to have a severe allergic reaction to a skin test.[43]
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    Try natural remedies. Certain natural treatments may help reduce allergy symptoms. You should always consult your doctor before trying any treatment, including ones that are natural or herbal. Even natural treatments can interfere with medical conditions and prescription medications.[44]
    • Vitamin C supplements (2,000 mg daily) may help improve allergy symptoms.[45][46]
    • Spirulina, a type of blue-green algae, may help reduce symptoms such as nasal discharge, sneezing, and congestion. It may also improve immune response, although more study is needed. take 4-6 500mg tablets a day.[47][48]
    • Butterbur (Petasites hybridus) has been shown to be effective at reducing allergy symptoms such as itchy eyes. It may also relieve nasal allergies.[49][50] Pregnant and breastfeeding women and young children should not use butterbur. Take 500mg a day or as directed by your doctor.[51]
    • Biminne is an herbal formulation in traditional Chinese medicine. It has been shown to be effective at improving allergy symptoms.[52] Speak with your doctor before taking biminne.[53]
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    Consider acupuncture. Some studies suggest that acupuncture can help relieve allergy symptoms, although more study is needed.[54][55] Talk with your doctor to see whether acupuncture is a good option for you.
    • The regulatory body for acupuncturists in the US is the National Certification Commission for Acupuncture and Oriental Medicine. Always make sure that you get treated by a licensed acupuncturist.[56]
    • Acupuncture is not commonly covered under most health insurance plans. Check with your insurance provider.


  • Some antihistamines can also work in a part of the brain that controls nausea and vomiting.[57]
  • As with any eye drop, avoid touching the container to your eye since this can cause contamination.[58]
  • Good sleep hygiene includes:[59] going to bed and getting up the same time each day, avoiding stimulation before sleeping, avoiding activities like exercise, watching TV, computer work, avoiding alcohol and caffeine before bed. You should associate your bed with sleep. Don’t read or do other work in bed.


  • Never take antihistamines over long periods of time without consulting a doctor. An underlying health condition can be masked by the antihistamine's ability to control symptoms.
  • Because antihistamines (especially first generation ones) can cause severe drowsiness, you should avoid driving or operating machinery when taking them.
  • Watch for negative side effects of antihistamines, including headaches, stomach pain, dry eyes and mouth.
  • Do not take antihistamines without first consulting with a doctor if you are taking any other prescription or non-prescription medications (including vitamins or herbal supplements).
  • Antihistamines are not the primary treatment for an anaphylactic reaction. Only Epinephrine will interrupt anaphylaxis.

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Categories: Allergies and Immunization