Why is my cat sleeping and not eating after an anti-nausea shot?

I am guessing the injection given was Cerenia. Side effects are uncommon with the use of this medication, but the most commonly noted side effects were: drooling, drowsiness, diarrhea, and appetite loss. I would be worried and I think he needs to get back to the vet. Were any x-rays or blood testing done? If not, that needs to be done to figure out what is going on. This sounds like it could be something more serious going on. If it was just a simple upset stomach he should be feeling MUCH better after that injection and not sleeping for 10 hours. I would be worried.

He may not feel like eating just yet as it is common it can take a day for his appetite to come back. I would let him rest today and let the medication start working. Try his food or even a little tuna in the morning. If he is still uninterested then you might want to get him rechecked for further testing

Cerenia is an anti-nausea medication, not a true appetite stimulant. A decrease in appetite is not a common side effect but was occasionally noted in safety studies. I think it’s more likely that Trixie’s decreased appetite is due to her disease rather than the medication. If you’re concerned you could ask your vet about other anti-nausea options but Cerenia is usually the most effective medication in cats.

Poor Sansa! It is possible these clinical signs are related to the injections. Steroids can make pets have many side effects and upset stomach is one of them. The antibiotic is typically better tolerated but it can also make pets have a upset stomach as well. It’s also possible this is coincidental. I recommend to call the veterinarian and alert them as to what you were seeing. They may ask to see Sansa to check her for a fever or other evidence of illness. Make sure Sansa eats and drinks today. You may try offering her some palatable canned cat food with some extra water added. If she continues to be a lethargic or not eating or drinking for 24 hours, she should be seen by the veterinarian as dehydration can settle in quickly. I hope she starts feeling better quickly and please feel free to post any additional questions.

No, this isn't normal behavior. While you can see a decrease in appetite and some lethargy, it's an unusual reaction to have a cat refusing to eat and drink, as well as not want to move. I would try to tempt her to eat by offering her some boiled white meat chicken (no bones) or soaking her food in tuna juice. If she still refuses to eat, then I would have her seen by a vet.

These are not side effects of the medications, these are symptoms related directly to the medical condition that caused the vomiting in the first place. if by tomorrow you see no improvement you will need to take her back to the vet.

I suspect Cleo is not feeling well and may be nauseous. Just like people, there are many conditions that can make pets feel sick. This could range from bacterial over growth to intestinal blockage. Also like us, diseases are best addressed early and this may result in a better prognosis. You need to monitor Cleo closely. If she is not eating or drinking well for 24 hours, if there is vomiting/diarrhea/coughing or signs of pain, I recommend to have her examined by the veterinarian today. If the lethargy lasts for 24 hours, your kitty also needs to be examined. The doctor will need to learn the underlying cause in order to give appropriate treatment. Bring in a stool sample in case the doctor needs to test it. At home, Cleo should continue resting. Encourage eating and drinking. Bring her the food and water. Fluid intake is very important when pets and people don't feel good. You may try offering her some boiled white meat chicken or canned tuna (in water not oil). Hopefully this will pass quickly. I hope Cleo starts feeling better quickly! Please feel free to post any additional questions.