Antihistamine Drugs

Antihistamine drugs are medications that counteract the effects of histamine, a chemical released by the body during allergic reactions. Histamine plays a key role in allergic symptoms such as itching, swelling, runny nose, and hives by binding to histamine receptors in the body. Antihistamines are primarily used to treat allergic conditions like hay fever, allergic rhinitis, urticaria (hives), and certain types of itching.

Uses of Antihistamine Drugs

Allergic Rhinitis: Antihistamines are commonly used to relieve symptoms such as sneezing, runny nose, and itching due to hay fever and other allergic reactions.

Urticaria (Hives): Both first- and second-generation antihistamines are effective in treating hives and itching.

Motion Sickness: First-generation antihistamines, like diphenhydramine and promethazine, are often used for their anti-nausea and sedative effects.

Insomnia: Some first-generation antihistamines are used as over-the-counter sleep aids due to their sedative properties.

Anaphylaxis: In cases of severe allergic reactions, antihistamines are used in conjunction with other treatments like epinephrine, although they are not sufficient on their own.

Side Effects

Sedation: First-generation antihistamines are known for causing drowsiness and are often avoided during daytime use unless sedation is desired.

Anticholinergic Effects: These can include dry mouth, blurred vision, constipation, and urinary retention, especially with first-generation antihistamines.

CNS Effects: First-generation antihistamines can impair cognitive function, reaction time, and coordination.

Minimal Side Effects with Second- and Third-Generation Antihistamines: These are generally well-tolerated and are preferred for long-term use due to fewer CNS effects.

Senior Black woman holding a tissue, wiping her nose

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First-Generation Antihistamines

These are older antihistamines that are effective at blocking the H1 histamine receptor but tend to cause sedation because they easily cross the blood-brain barrier.

Second-Generation Antihistamines

These are newer antihistamines designed to minimize sedation and other central nervous system (CNS) effects. They are preferred for long-term treatment of allergies.