Hydroxyzine is a prescription medication known as a first-generation antihistamine. It is commonly used to treat conditions like anxiety, tension, and allergic itching. Motion sickness (kinetosis) is a common inner ear disturbance characterized by symptoms like nausea, vomiting, and dizziness, triggered by real or perceived motion.
Efficacy and Clinical Use for Motion Sickness
Hydroxyzine is not typically considered a first-line treatment for motion sickness, unlike dedicated anti-nausea drugs such as scopolamine or meclizine. However, its pharmacological profile makes it effective for this purpose, and it is sometimes prescribed off-label by healthcare providers. Its effectiveness stems from its properties as a sedating antihistamine and its ability to block certain chemical messengers in the central nervous system.
The antiemetic, or anti-vomiting, effects of hydroxyzine are well-established, leading to its historical use for managing nausea and vomiting from various causes. Its classification as a first-generation antihistamine is key because this class of drug can cross the blood-brain barrier, directly influencing the areas of the brain that process balance and trigger nausea.
A physician might opt to prescribe hydroxyzine for motion sickness when a patient also experiences significant anxiety related to travel or when a sedating effect is beneficial. The drug’s calming action can help manage the overall distress associated with severe kinetosis.
Mechanism of Action in Preventing Nausea
Hydroxyzine acts as a potent H1 receptor antagonist, blocking histamine activity at H1 receptors found throughout the body, including in the brain. The vestibular system in the inner ear, which regulates balance, communicates with the central nervous system using various neurotransmitters, including histamine.
Motion sickness occurs when the sensory input from the eyes, inner ear, and body do not match, leading to an over-stimulation of the vestibular nerves. These over-stimulated nerves send signals to the brain’s vomiting center and the chemoreceptor trigger zone (CTZ). By blocking H1 receptors in these central areas, hydroxyzine dampens the excessive nerve signals originating from the inner ear’s balance apparatus.
Hydroxyzine also possesses notable anticholinergic properties, blocking the action of acetylcholine, another neurotransmitter involved in transmitting signals from the vestibular system. This dual action, blocking both histamine and acetylcholine pathways, contributes significantly to its effectiveness in preventing nausea and vomiting caused by motion.
Dosing and Common Side Effects
Hydroxyzine is available in oral forms, such as tablets and capsules, and is only available with a prescription. For anti-nausea or anti-anxiety purposes, adult doses can range from 25 milligrams (mg) up to 100 mg, typically taken three to four times a day, though the specific dosage for motion sickness is determined individually. Since motion sickness prevention is most effective, the medication is generally taken shortly before the onset of travel.
The most common side effect of hydroxyzine is marked sedation and drowsiness, a direct result of its action in the central nervous system. This sedative effect can impair a person’s ability to safely operate a vehicle or heavy machinery and is a major consideration for use during travel. Patients should avoid consuming alcohol or taking other sedating medications while using hydroxyzine, as this can intensify the drowsiness.
Other common adverse effects are related to the drug’s anticholinergic properties and include dry mouth and blurred vision. Hydroxyzine should be used with caution in elderly individuals, who are more susceptible to confusion and excessive sleepiness. It is also contraindicated in patients with a history of heart rhythm issues, specifically a condition known as prolonged QT interval, due to a risk of serious cardiac side effects.