Can antibiotics make cats sleepy

Amoxicillin is not known to cause sleepiness or lethargy as a common side-effect, but all cats respond to antibiotics differently. The most common side-effect for this drug is diarrhoea and perhaps vomiting. It could be that the infection itself is making the cat lethargic, but only a vet will be able to tell you.

If you are worried about your cat, even if it is on antibiotics, call your vet.