Polyphagia is a medical term for excessive or ravenous hunger. It can be caused by a medical condition, such as diabetes, but can also be a symptom of mental health disorders like anxiety and depression. In cats, polyphagia is often caused by hyperthyroidism, which is a hormonal imbalance that causes the body to overproduce thyroid hormone. This excess hormone speeds up the metabolism, which in turn increases appetite. Polyphagia can also be caused by certain types of cancer, such as lymphoma. If your cat is eating more than usual and you cannot find an underlying medical cause, it's important to talk to your veterinarian or a behavioral specialist about possible psychological causes.