My healthy 5 yr old cat had a bad reaction to this, my other cat seemed fine, so no connection was made until it was too late, she suffered for 9 months, with vets having no clue until I foolishly gave her the last dose. She was a ginger shorthair, her symptoms were a dry cough, lots of moulting, greasy coat, weight loss, and tiredness, it cost me £100's trying to find out what was wrong. And I will never forgive myself for giving this poison to her. I found her with big pupils fitting and whimpering like she was having terrible halucinations, the vet put her to sleep, but honestly, I think she only had minutes left. If you have used this, please watch for these symptoms and make sure treatment is stopped. RIP Marceline.