Antihistamines are drugs that block histamine receptors, reducing allergic reactions. They come in over-the-counter (OTC) and prescription forms, including cetirizine, loratadine, and diphenhydramine.
Histamine is a chemical your immune system releases during an allergic reaction. It causes symptoms like sneezing, itching, and runny nose. Antihistamines bind to histamine receptors, preventing histamine from attaching and triggering these symptoms.
| Type | Examples | Sedation Level |
|---|---|---|
| First-generation | Diphenhydramine, chlorpheniramine | High |
| Second-generation | Cetirizine, loratadine, fexofenadine | Low |
| Third-generation | Desloratadine, levocetirizine | Very low |
Antihistamines treat allergies, hay fever, hives, and insect bites. Some also help with motion sickness and insomnia. For example, diphenhydramine is found in sleep aids like Unisom.
Many assume all antihistamines cause drowsiness. While first-generation antihistamines do, second- and third-generation options are less likely to. The FDA notes that second-generation antihistamines are generally safer for daytime use.
Another myth is that antihistamines cure allergies. They only relieve symptoms temporarily. Long-term allergy management may require other treatments, such as immunotherapy.
I once took a first-generation antihistamine before driving and felt excessively drowsy. Since then, I've opted for second-generation options during the day.
For more details on choosing the right antihistamine, see this guide.
Antihistamines are effective for allergy relief, with options available for both daytime and nighttime use. Understanding the differences between generations helps you pick the right medication.