Antihistamines are a class of medications that are commonly used to treat symptoms associated with allergies, such as sneezing, itching, watery eyes, and runny nose. Histamines are chemicals released by the body’s immune system during an allergic reaction. They cause inflammation and other symptoms associated with allergies.
Antihistamines work by blocking the effects of histamines, thereby reducing or preventing allergic symptoms. They can be taken orally, applied to the skin (topical), or administered through injections, depending on the specific formulation and intended use.
There are two main types of antihistamines:
- First-generation antihistamines: These antihistamines tend to cause more drowsiness and can have a sedative effect, which can be beneficial for treating insomnia or allergic reactions at night. However, their sedating effects can impair daytime functioning. Examples include diphenhydramine (Benadryl), chlorpheniramine (Chlor-Trimeton), and hydroxyzine (Vistaril).
- Second-generation antihistamines: These antihistamines are less likely to cause drowsiness because they are designed to be less sedating and have a longer duration of action. They are often preferred for daytime use. Examples include loratadine (Claritin), cetirizine (Zyrtec), fexofenadine (Allegra), and desloratadine (Clarinex).
Antihistamines are generally safe when used as directed, but they can cause side effects such as drowsiness, dry mouth, dizziness, and constipation. It’s essential to follow the dosage instructions provided by a healthcare professional and to avoid combining antihistamines with alcohol or other sedating medications without consulting a doctor.