Antihistamine (aka histamine antagonist) inhibits the action of histamine, used to relieve allergies.
Histamine H1-receptor antagonist, used to Tx allergic reactions in the nose (e.g. itching, runny nose, and sneezing), which are used off-label for insomnia. They are also used to Tx motion sickness or vertigo caused by problems w/ the inner ear, by binding to H1 receptors in mast cells, smooth muscle, and endothelium in the body and tuberomamillary nucleus in the brain. Examples include:
3rd generation antihistamine, as it is less able to pass the BBB and cause sedation:
Fexofenadine (Allegra, Telfast)
2nd generation antihistamines, as they are less able to cross the BBB and thus have diminished effects on the CNS, thus less likely to induce drowsiness or interfere w/ memory formation:
1st generation antihistamines:
Quetiapine (an antipsychotic, Seroquel)
Histamine H2-receptor antagonist, used to Tx gastric acid conditions (e.g. peptic ulcers and acid reflux), by binding to H2 receptors in the upper GI tract, primarily in the stomach