Hi, I'm Dr. Nenad. Cat vomiting. An occasional hairball or upset stomach can cause your cat to vomit. However, frequent vomiting is never something to ignore . It can be caused by hairballs , eating too quickly, dietary changes, parasites, or more serious conditions affecting the stomach, kidneys, or liver. If your cat is vomiting more than once a week, repeatedly in one day, or you notice blood, lethargy, or loss of appetite, it's time to see a veterinarian. Early diagnosis can make all the difference. So, don't wait if your cat's vomiting seems unusual.