Chances are you’ve taken an antihistamine this week. Antihistamines are common drugs that can be purchased without a prescription and are used to treat short-lived allergic reactions, like a sneezing fit or an itch.
As the name suggests, an antihistamine drug acts against the activity of the histamine receptor — proteins that bind to a compound in the body called histamine. This compound consists of two attached to each other: ethylamine (CH3CH2NH2) and imidazole (C2N2H4), the latter being a ring.
Depending on its location, histamine performs broadly four types of functions, each involving different histamine receptors called H1, H2, H3, and H4. The H1 receptor is found mostly in the inner surface of blood and lymphatic vessels, neurons, and smooth muscle cells. H1 antihistamines are used to block the effects of minor allergies. Certain cells in the gastric glands release histamine, which encourage nearby parietal cells with H2 receptors to release gastric acid for digestion.
