Cats that are depressed and not eating are sick and should be seen promptly by a veterinarian. These nonspecific signs are commonly caused by fever. Fevers will turn off a cat's appetite and energy. No safe over-the-counter treatment for fever is available for cats. Aspirin, acetaminophen and ibuprofen are toxic to cats.
When examining a cat with symptoms such as a loss of appetite or depression, a veterinarian will try to localize a site of infection or location of a problem. Further diagnostic testing may be needed to assess the cat's condition. Often the cat may receive symptomatic treatment after an initial examination. This treatment is aimed at relieving the symptoms and making the pet feel better. Symptomatic treatment can involve fluids, antibiotics, appetite stimulants, force-feeding or an anti-inflammatory drug.
If a cat does not respond to supportive care within a couple of days, it is vital to follow up. Cats that do not eat can develop secondary health problems, such as hepatic lipidosis, or fatty liver disease, that can be more life threatening than the original problem if the cat's metabolic functions are compromised.