07/02/2026
Swipe through this post if your cat has been losing weight and you are not sure why. It is one of the questions we hear most often, and it deserves a straight answer.
Weight loss in cats can have many causes, but when it keeps happening alongside other signs like a swollen belly, labored breathing, a persistent low fever, or sudden changes in behavior, it is worth taking seriously right now, not in a few weeks.
One condition that can show up this way is FIP, or Feline Infectious Peritonitis (FIP). It tends to come on gradually, which is part of why owners sometimes wait before calling the vet. Please do not wait.
The good news is that FIP is no longer the dead end it once was. Cats diagnosed today have a real path forward, and your vet can walk you through what that looks like for your cat specifically.
If your cat is being treated with an antiviral approach, you may hear the compound GS-441524 mentioned. Any decision about treatment, timing, and monitoring should be made entirely by your veterinarian.
Your first step is to get your cat seen and tested. Early diagnosis gives your vet more to work with.
For guidance on FIP, what to ask your vet, and how to find support in the GCC, visit curefipgcc.com.