Allergies Common Treatments Antihistamines and How They're Used By Daniel More, MD Daniel More, MD Daniel More, MD, is a board-certified allergist and clinical immunologist with a background in internal medicine. Learn about our editorial process Updated on June 14, 2022 Medically reviewed by Daniel More, MD Medically reviewed by Daniel More, MD Daniel More, MD, is a board-certified allergist and clinical immunologist with a background in internal medicine. Learn about our Medical Expert Board Print Table of Contents View All Table of Contents Common Uses Types of Antihistamines Common Side Effects Frequently Asked Questions Antihistamines are a class of drugs primarily used to relieve allergies. They do so by blocking a chemical known as histamine that is released by the immune system whenever the body is confronted by an allergy-causing substance (allergen). By preventing histamine from attaching to cellular receptors in the skin and mucus membranes of the eyes, nose, and respiratory tract, symptoms of allergy—such as sneezing, itchy eyes, postnasal drip, and, hives—can be temporarily relieved. Antihistamines may also be useful in treating motion sickness, nausea, sinusitis, and eczema. This article explains the different uses of antihistamine drugs and lists some of the more common over-the-counter (OTC) and prescription formulations. Mario Tama Collection / Getty Images Common Uses of Antihistamines Antihistamines are used to treat various allergic conditions and are available in oral, nasal, eyedrop, and injected formulations. Among the conditions they most commonly treat are allergic rhinitis, allergic conjunctivitis, and hives. Allergic Rhinitis (Hay Fever) Allergic rhinitis, also known as hay fever, is an allergic response that causes sneezing, runny nose, and itchy, watery eyes. It can occur seasonally or year-round, due primarily to tree or grass pollens. Oral antihistamines can generally improve hay fever symptoms within an hour or two. Newer oral antihistamines, such as Xyzal (levocetirizine), Zyrtec (cetirizine), Allegra (fexofenadine), and Clarinex (desloratadine), are very effective for the treatment of hay fever. Older antihistamines, like Benadryl (diphenhydramine), Chlor-Trimeton (chlorpheniramine), and Vistaril (hydroxyzine) work well but can be sedating and cause other side effects. There are also nasal sprays like Astelin (azelastine) and Patanase (olopatadine) that are used to treat allergic rhinitis (nasal allergy). How Hay Fever Is Treated Allergic Conjunctivitis Many of the same allergens that cause hay fever can also cause allergic conjunctivitis. an allergic reaction involving the covering of the eye (known as the conjunctiva). These include airborne allergens (like pollen, dust, perfume, and pet dander) but also substances placed in or around the eye (like makeup and contact lens solution). Oral antihistamines can help treat symptoms of eye allergies. There are also antihistamine eye drops such as Optivar (azelastine), Emadine (emedastine), Visine-A (pheniramine), and Alaway (ketotifen). Urticaria (Hives) Urticaria, better known as hives, is a raised, itchy rash triggered by a reaction to food, medicine, or other irritants. In some cases, the cause of an outbreak is unknown. Oral antihistamines are the main treatment for hives. Newer "non-drowsy" antihistamines, such as Zyrtec or Claritin, are preferred over the older antihistamines like Benadryl or Vistaril. With that said, if the itchiness of hives is keeping you up at night, older-generation antihistamines may help you sleep soundly. Topical antihistamines, present in many over-the-counter anti-itch creams, should not be used with oral antihistamines. Certain ones, such as Benadryl cream, have been known to trigger contact dermatitis when taken with its oral version. Other Uses Antihistamines are used for the treatment of other allergic conditions. Some of the approved uses of antihistamines include: Allergic skin reactions Sinusitis (sinus inflammation) Angioedema (the generalized swelling of deeper tissues) Eczema (atopic dermatitis) Allergic drug reactions Bronchitis (inflammation of the bronchial tubes of the lungs) Motion sickness Nausea and vomiting OTC and Prescription Antihistamines There are both OTC and prescription antihistamines used for the treatment of allergies. The choice varies by the type and severity of allergy you have, as well as whether the condition is acute (rapidly developing) or chronic (persistent or recurrent). Not all antihistamines work equally well for all allergic conditions. If buying an OTC antihistamine, speak with your healthcare provider or pharmacist to determine whether it is the best option for you as well as the potential risks. OTC Alaway (ketotifen) Allegra (fexofenadine) Benadryl (diphenhydramine) Claritin (loratadine) Chlor-Trimeton (chlorpheniramine) Dimetane (brompheniramine) Tavist (clemastine) Visine-A (pheniramine eyedrops) Xyzal Allergy 24HR (levocetirizine) Zyrtec (cetirizine) Prescription Astelin (azelastine nasal spray) Clarinex (desloratadine) Emadine (emedastine eyedrops) Livostin (levocabastine eyedrops) Optiva (azelastine eyedrops) Palgic (carbinoxamine) Patanase (olopatadine nasal spray) Periactin (cyproheptadine) Vistaril (hydroxyzine) Common Side Effects Second-generation antihistamines (like Allegra, Claritin, Tavist, Xyzal, and Zyrtec) tend to have far fewer side effects than older-generation versions. Common side effects include: HeadacheStomach painFatigueNervousnessDiarrhea First-generation antihistamines (such as Benadryl, Chlor-Trimeton, and Vistaril) also have these side effects but can cause additional ones as well, including: DrowsinessConstipationDifficulty urinatingDry mouth Because first-generation drugs are more sedating, they are generally avoided for daytime use. They can also diminish your ability to operate motor vehicles or heavy machinery. Of the second-generation antihistamines, Allegra is the only one that is truly considered to be non-sedating. Certain antihistamines may also cause weight gain. According to the American Academy of Asthma, Allergy & Immunology, both older drugs like Periactan and newer ones like Allegra and Zyrtec are linked to an increased risk of obesity. It is thought that the suppression of histamine, which is known to reduce appetite, can increase appetite in people on chronic antihistamine treatment. When Your Allergy Medicine Doesn't Work Anymore Summary Antihistamines are used to treat allergies. They work by suppressing a chemical called histamine that triggers allergy symptoms like rash, runny nose, watery eyes, and sneezing. They may also be useful in treating motion sickness, nausea, sinusitis, and eczema. Antihistamines are available over the counter and by prescription in oral, topical, nasal, eyedrop, and injected formulations. Newer-generation antihistamines like Allegra (fexofenadine) and Claritin (loratadine) tend to cause less drowsiness than older-generation ones like Benadryl (diphenhydramine). A Word From Verywell As useful antihistamines are in treating allergy symptoms, they can cause problems if overused. This includes the risk of dependency if antihistamine eyedrops are overused. If you suffer from chronic allergies and find that you need to take antihistamines every day, it may be time to ask your healthcare provider for a referral to a specialist known as an allergist. An allergist can perform tests to see which allergens you are reacting to. They may then be able to reduce your sensitivity to these allergens with allergy shots and other forms of allergy immunotherapy. Do Allergy Shots Really Work? Frequently Asked Questions What are antihistamines used for? Antihistamines are most often used to treat allergy symptoms. Histamine is a chemical the body releases in response to an allergen that causes itchiness, sneezing, congestion, and watery eyes. Antihistamines work by blocking the action of histamine. What are the different types of antihistamines? Antihistamines can be either H1 blockers or H2 blockers, named for the histamine receptor they block. H1 blockers like Allegra (fexofenadine) and Zyrtec (cetirizine) are typically used to treat seasonal or environmental allergies. H2 blockers like Pepcid (famotidine) and Tagamet HB (cimetidine) are commonly used to reduce stomach acid. Can you become addicted to antihistamines? Antihistamines generally have a low risk of abuse. However, there have been reports of people becoming dependent on older antihistamines like Benadryl (diphenhydramine) if taken at high doses for extended periods of time. Withdrawal may occur once the drug is stopped. 9 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Scadding GK. Optimal management of allergic rhinitis. Arch Dis Child. 2015;100(6):576-82. doi:10.1136/archdischild-2014-306300 Church MK, Church DS. Pharmacology of antihistamines. Indian J Dermatol. 2013;58(3):219-24. doi:10.4103/0019-5154.110832 Ross A, Fleming D. Hayfever--practical management issues. Br J Gen Pract. 2004;54(503):412-4. PMID: 15186559 Rathi VM, Murthy SI. Allergic conjunctivitis. Community Eye Health. 2017;30(99):S7–S10. Bernstein JA, Lang DM, Khan DA, et al. The diagnosis and management of acute and chronic urticaria: 2014 update. J Allergy Clin Immunol. 2014;133(5):1270-7. doi:10.1016/j.jaci.2014.02.036 University of Maryland Center of Excellence in Regulatory Science and Innovation. Diphenhydramine chloride. American Academy of Asthma, Allergy & Immunology. Antihistamines and weight gain. MedlinePlus. H2 blockers. Gracious B, Abe N, Sundberg J. The importance of taking a history of over-the-counter medication use: a brief review and case illustration of "PRN" antihistamine dependence in a hospitalized adolescent. J Child Adolesc Psychopharmacol. 2010;20(6):521–4. doi:10.1089/cap.2010.0031 Additional Reading Seresirikachorn K, Khattiyawittayakun L, Chitsuthipakorn W, Snidvongs K. Antihistamines for treating rhinosinusitis: systematic review and meta-analysis of randomised controlled studies. J Laryngol Otol. 2018;132(2):105-10. doi:10.1017/S002221511700192X. By Daniel More, MD Daniel More, MD, is a board-certified allergist and clinical immunologist. He is an assistant clinical professor at the University of California, San Francisco School of Medicine and currently practices at Central Coast Allergy and Asthma in Salinas, California. See Our Editorial Process Meet Our Medical Expert Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit