Zyrtec has been available by prescription for years, but now, for the first time it's available over the counter. It provides prescription-strength, 24-hour, indoor and outdoor allergy relief. Get relief from sneezing, runny nose, itchy watery eyes and itchy throat or nose. Zyrtec is a fast acting, once-a-day medication that relieves symptoms of indoor and outdoor allergies. For most people, Zyrtec begins to work in as little as 1 hour and provides effective 24-hour relief.