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An antihistamine is a drug that blocks the action of histamine, a naturally occurring chemical in the body. Histamine is responsible for various reactions, including sneezing, itching, and inflammation. Antihistamines are commonly used to treat allergies, hay fever, and other conditions that cause these symptoms.

Antihistamines work by blocking histamine receptors in cells in the body. This prevents histamine from binding to the cells and causing its typical reactions. By blocking these receptors, antihistamines can reduce or eliminate symptoms associated with allergies and other conditions. There are two main types of antihistamines:

First-generation antihistamines, such as diphenhydramine (Benadryl), are effective at relieving allergy symptoms but can cause drowsiness and other side effects.

Second-generation antihistamines, such as loratadine (Claritin) and cetirizine (Zyrtec), are better tolerated and less likely to cause drowsiness.

The most common side effects of antihistamines include drowsiness, dry mouth, dizziness, and blurred vision. Some antihistamines can also interact with other medications, so it is essential to talk to your doctor before taking any antihistamines.

In addition to treating allergies, antihistamines may also treat hives, itching, and other skin reactions. They may also be used to help prevent nausea and vomiting caused by motion sickness and to help treat insomnia.

Antihistamines are available over-the-counter and by prescription and come in various forms, such as tablets, capsules, liquids, nasal sprays, and eye drops. They should be used as directed by a healthcare professional and should not be taken in larger amounts or for longer than recommended.

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  • Allergy: Types of Antihistamines. (2020, June 24). Retrieved from
  • Antihistamines. (2020, June 15). Retrieved from
  • Antihistamines. (2020, June ). Retrieved from