I hate to admit how much experience I have with Prozac cats.
Anyway, Leopold is on Prozac for spraying. It's been effective. The biggest side effect is the lack of spraying, honestly. There's no other obvious behavior, attitude, or energy level difference with or without the Prozac. For the first week or two, he did have a noticeably decreased appetite, but that is typical and temporary. He eats well now.
It does take awhile to start working. In some cats, you see no change at all in the first month or so. In others (like Leopold), you might see ups and downs over the course of the first few weeks, finally leveling out and proving effective after 6 weeks or so. After a few weeks, the spraying was cut down by 50% I would say. Now, at 6-7 weeks I hardly see him even thinking about doing it.
Far too often, I hear that people tried it for "a month" and it "didn't work". Trying it for only a month is not worth the effort, in my experience. From what I've read, Prozac is effective for spraying 90% of the time. From what I understand, the long term success rate is much better if it's used for at least several months, maybe 6.
Prozac has a very long elimination half life, which is the reason for the lapse before it works. That also means that it could be stopped abruptly...as it would naturally take at least a few weeks to be out of their system. I was told to taper off, though - when the time comes.
I think the concern re. the blood work is to do it before hand, to make sure there are no underlying liver (or kidney) issues that could be aggravated by the meds.
My vet has it in gel caps, just a small amount of powder that even picky Leopold will eat in wet food. It's about $18/month. I have picked up the solid pills from Walgreen's for $12/month too (works if the cat likes pill pockets). He's on 2.5mg, once a day.
The veterinary patient info sheets for both...http://www.drsfostersmith.com/Rx_Inf..._buspirone.pdfhttp://www.drsfostersmith.com/Rx_Inf...fluoxetine.pdf