Vistaril etc. (hydroxyzine) is a first generation (H1 blocker) antihistamine used to relieve itching caused by allergic conditions, to treat anxiety disorders and to treat insomnia. Histamine is a central nervous system neurotransmitter, and hydroxyzine works by blocking the H1 histamine receptors in the brain.
By blocking histamine, Hydroxyzine and other first generation antihistamines reduce anxiety, produce drowsiness and, in high dosages, impair psychomotor performance of complex tasks. Mild tolerance to the sedative effects may occur with long term use. The first generation antihistamines have anticholinergic properties, causing dry mouth, increased heart rate and decreased gastro intestinal activity.