Not medical advice: Hydroxyzine may take a number of days to be completely eliminated from your system. There are many variables that will affect the duration. These factors include how healthy your kidneys are (hydroxyzine is metabolized in the kidneys) as well as the health and functioning of everything from your biliary ducts through your lower intestine since hydroxyzine is excreted from the body through feces.
In general the effects of hydroxyzine are felt within 30-60 minutes of being administered. Methods of administration are either orally or intramuscular. The half-life of hydroxyzine is three hours in adults, meaning in three hours its effect or presence is halved.
According to Drugs.com, Vistaril (hydroxyzine) reduces activity in the central nervous system. It also acts as an antihistamine that reduces the natural chemical histamine in the body. Histamine can produce symptoms of sneezing and runny nose, or hives on the skin.
It is used as a sedative to treat anxiety and tension. It is also used together with other medications given for anesthesia. Vistaril may also be used to control nausea and vomiting.