Such properties have been attributed to hydroxyzine in several cases, particularly in patients treated for neuropsychological disorders, as well as in cases where overdoses have been observed. While there are reports of the "hallucinogenic" or "hypnotic" properties of hydroxyzine, several clinical data trials have not reported such side effects from the sole consumption of hydroxyzine, but rather, have described its overall calming effect described through the stimulation of areas within the reticular formation. The hallucinogenic or hypnotic properties have been described as being an additional effect from overall central nervous system suppression by other CNS agents, such as lithium or ethanol.Hydroxyzine exhibits anxiolytic and sedative properties in many psychiatric patients. One study showed that patients reported very high levels of subjective sedation when first taking the drug, but that levels of reported sedation decreased markedly over 5-7 days, likely due to CNS receptor desensitization. Other studies have suggested that hydroxyzine acts as an acute hypnotic, reducing sleep onset latency and increasing sleep duration — also showing that some drowsiness did occur. This was observed more in female patients, who also had greater hypnotic response. The use of sedating drugs alongside hydroxyzine can cause oversedation and confusion if administered at high doses—any form of hydroxyzine treatment alongside sedatives should be done under supervision of a doctor.Because of the potential for more severe side effects, this drug is on the list to avoid in the elderly.In 2015, the European Medicines Agency (EMA) announced a small but definite risk of QT prolongation associated with the use of hydroxyzine.
These have also been confirmed in both recent and past studies to have no adverse effects on the liver, blood, nervous system, or urinary tract.Use of hydroxyzine for premedication as a sedative has no effects on tropane alkaloids, such as atropine, but may, following general anesthesia, potentiate meperidine and barbiturates, and use in pre-anesthetic adjunctive therapy should be modified depending upon the state of the individual.Hydroxyzine is used as a non-barbiturate tranquilizer and for the treatment of neurological disorders, such as psychoneurosis and other forms of anxiety or tension states.Doses of hydroxyzine hydrochloride used for sleep range from 25 to 100 mg. As with other antihistamine sleep aids, hydroxyzine is usually only prescribed for short term or "as-needed" use since tolerance to the CNS effects of hydroxyzine can develop in as little as a few days. Contraindications
The administration of hydroxyzine in large amounts by ingestion or intramuscular administration during the onset of pregnancy can cause fetal abnormalities. When administered to pregnant rats, mice and rabbits, hydroxyzine caused abnormalities such as hypogonadism with doses significantly above that of the human therapeutic range.In humans, a significant dose has not yet been established in studies and, by default, the Food and Drug Administration (FDA) has introduced contraindication guidelines in regard to hydroxyzine. Use by those at risk for or showing previous signs of hypersensitivity is also contraindicated. Hydroxyzine is contraindicated for intravenous (IV) injection, as it has shown to cause hemolysis.