However, high doses can still induce the central nervous system drowsiness.
Antihistamines are a class of agents that block histamine release from histamine-1 receptors and are used to treat the symptoms of an allergic reaction, such as edema (swelling), itch, inflammation (redness), sneezing, or a runny nose or watery eyes.
They do, however, have the potential for negative effects if taken with other drugs, so let your doctor know if you are taking more than one medication.
Also called histamine antagonists, antihistamines are administered to fight allergic reactions, in which cases sleepiness is considered a possibly undesirable side effect.
Antihistamines make your sleepy by antagonizing central histimine-1 (H-1) receptors in the brain.
The ones you see in over-the-counter sleep aids are usually diphenhydramine and hydroxyzine.
In common use, the term "antihistamine" refers only to H In type I hypersensitivity allergic reactions, an allergen (a type of antigen) interacts with and cross-links surface Ig E antibodies on mast cells and basophils.
Once the mast cell-antibody-antigen complex is formed, a complex series of events occurs that eventually leads to cell degranulation and the release of histamine (and other chemical mediators) from the mast cell or basophil.