Two cats ago, I adopted an older cat with arthritis and a tumor on his liver, who received Gabapentin for "pain and anxiety" which quite frankly I think was more for the anxiety, which he clearly did have. The thing is, we know that long-term constant stress leads to inflammation and that long term inflammation can damage our physiologies in a number of ways. Or the physiologies of our animal companions. This cat was already 13 years old when he was rescued from the streets, so who knows what kind of trauma he had endured. Proper care and a nice foster home made all the difference in the world, and in spite of the inoperable tumor on his liver, he outlasted his prognosis by almost 2 years (and was actually the best cat ever.)