Q. what causes a cat to gag continually
DESTINI R. HOLLOWAY, DVM
A. Gagging is a pretty broad symptom but this is a sign of either nausea of the pet trying to get something to come back up that is causing irritation to the GI tract. So some things that can cause this are gastritis (inflamed stomach due to dietary indiscretion or parasites), foreign body ingestion, hair balls.
If your pet is attempting to vomit continuously for over 12 hrs unsuccessfully then he needs to be seen. Especially if this is accompanied by vomiting, lethargy or inappetance. This is highly suspicious of a foreign body if he fits the criteria. A vet should examine him by palpating his stomach and potentially doing an abdominal x-ray to look for any foreign body's, so that they can recommend the next best treatment for your pet's care.
DAVID ELBEZE, DVM, MRCVS
A. Usually nausea or hairballs. nausea happens as a result of wanting to throw up, this can be caused by a gastrointestinal condition, a tumor or renal failure.
Hairballs happens as a result of grooming, it's more common in long haired cat but can also occur in short haired cats.
If your cat gags constantly you should take him to your veterinarian and get him checked.