hydroxyzine HCl oral Uses Hydroxyzine is used to treat itching caused by allergies. It is an antihistamine and works by blocking a certain natural substance (histamine) that your body makes during an allergic reaction. Hydroxyzine may also be used short-term to treat anxiety or to help you feel sleepy/relaxed before and after surgery. How to use hydroxyzine HCl oral Side Effects Drowsiness, dizziness, blurred vision, constipation, or dry mouth may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.