I don't have experience with dogs, but I'm on gabapentin. I know I was prescribed 900mg 3x a day. I now only take 600 1x a day. So you can go pretty high. As for side effects, the only one I've had is that when taken with my sleeping meds it helps me sleep a bit better. On it's own though I had no side effects. My father was on it to help with palliative care for fibrosarcoma. It was the only thing that helped, even morphine and other high power stuff weren'thelping him. It is really only good for nerve pain, if he isn't having nerve pain, I wouldn't bother giving it to him.