Why is my cat losing weight, weak, and lethargic after deworming?

The deworming pill and the symptoms you described have nothing to do with each other, if he is losing his fur and losing weight he is suffering from something serious. Sudden weight loss is always a very big warning light that should not be taken lightly, it's usually a sign of an internal disease that needs to be investigated, i strongly recommend taking him to the vet in order to get it checked, he will need to have a blood test done and possibly an xray as well in order to attempt to diagnose the reason for these symptoms.

Thanks for using Petco Pet Education Center, formerly Petcoach. I agree that a heavy worm burden can cause what you’re describing. In fact, it is the most likely reason. You can try an over the counter cat dewormer from a pet store. Follow the directions exactly in terms of amount and number of treatments. Hopefully, that’s all it takes to get her feeling better. Unfortunately, there are other (much less common) things that can cause large belly, weight loss, and lethargy including: FIP, heart failure, liver failure, cancer, protein problems, etc. So, if the dewormer doesn’t help, you may have to decide if you’d want to take her to the vet for further testing or if you’d like her humanely euthanized, etc. Best wishes and thank you so much for taking care of this stray!

I would call your vet with this update. I would not expect these symptoms in a normal cat with tapeworms. Occasionally, in pets with a really large worm burden, the dying worms can cause a blockage in the intestines. The vet should be able to help you decide if Christina needs to be re-evaluated.

Thanks for using Petco Pet Education Center, formerly Petcoach! Without seeing the cats, it is hard to say. I recommend taking them to the vet with a fresh stool sample to rule out other parasites. Not all deworming medications treat all intestinal parasites. If negative, I would have both cats tested for feline leukemia and FIV. These are infectious diseases that could cause poor growth. Good luck and kisses to the kittens!

It sounds like there could be an underlying issue. Tapeworms don't usually cause coughing and lethargy in cats. Your cat should be examined by a vet to determine the exact cause and treat the problem. Your vet can run labwork and take an xray, if needed, to help diagnose and then determine the best way to treat.

Intestinal parasites can be picked up from the environment. If this is a tapeworm you saw (looks similar to a grain of rice), fleas can transmit tapeworm to cats. I would recommend treating Venus with a product called Profender, which will treat intestinal parasites including tapeworm. I would also consider using a flea and tick preventative such as Revolution or Frontline. I would also consider bringing a stool sample to a veterinarian to help diagnose what kind of intestinal parasites these could be. I hope this helps! Please let me know if you have any other questions or concerns and I would be more than happy to help you further.

Sudden weight loss is always a very big warning light that should not be taken lightly, it's usually a sign of an internal disease that needs to be investigated, i strongly recommend taking Winter to the vet in order to get it checked, he will need to have a blood test done and possibly an xray as well in order to attempt to diagnose the reason for these symptoms.