Antihistamines are a class of drugs that help treat conditions caused by too much histamine, a chemical created by your body’s immune system. They are most commonly used to relieve symptoms of allergies, such as hay fever, hives, conjunctivitis, and reactions to insect bites or stings. Antihistamines work by blocking some of what histamine does, which helps to alleviate a wide range of symptoms such as congestion, sneezing, runny nose, itchy or watery eyes, itching, skin rashes, hives, and nausea.

Antihistamines are divided into two major subtypes: H-1 receptor antagonists or H-1 blockers, which are used to treat allergy symptoms, and H-2 receptor antagonists or H-2 blockers, which are used to treat gastrointestinal conditions, including acid reflux, peptic ulcers, and motion sickness.

There are several different forms of antihistamines, including tablets, capsules, liquids, syrups, creams, lotions, gels, eyedrops, and nasal sprays. Non-drowsy antihistamines are generally the best option, as they are less likely to make you feel sleepy. However, types that make you feel sleepy may be better if your symptoms stop you from sleeping.

It is important to note that antihistamines may interact with other medications you are taking, so it is essential to check the leaflet that comes with your medication or ask your pharmacist for advice if you are unsure which medicine to try. Some antihistamines cause less sleepiness than others, such as cetirizine (Zyrtec), desloratadine (Clarinex), fexofenadine (Allegra), levocetirizine (Xyzal), and loratadine (Alavert, Claritin) . Pregnant women should speak with their doctor before taking antihistamines, and people with certain medical conditions should also check with their doctor before taking them.