
Our large breed dog who suffered with a degenerative condition with his spine was on a bit of a mix of drugs.
He didn't get on with metacam so that was changed to previcox. He was given tramadol for pain relief but rarely needed them as his condition wasn't one that came with any great deal of pain (he had slipped discs & hips dysplasia in his youth but the last couple of years he lost the use of his legs (other than in water) and ultimately had Degenerative Myelopathy, which is mostly a pain free ailment, so we only used the Tramadol if he seemed to be in pain at any time.
We also had him on Cosequin and Aktivait supplements as well as Green Lipped Mussel powder.
In the last years when he couldn't walk at all he used to get restless at night. That is when they added Gabapentin and Diazepam. However, the Gabapentin completely stopped any restlessness or discomfort at night (we never needed the Diazepam until the very end when he developed cancer).
I think the Gabapentin worked well dealing with generalised pain/discomfort, night anxiety or restlessness and the Tramadol was a handy pain killer which we could give as and when we saw any pain. I am pretty certain the gabapentin working so well is probably why we didn't need the tramadol or diazepam very often. The swimming also seemed to relax him afterwards as well as keeping his muscle tone up so he had no muscle wastage at any point.
We suffered no ill side-effects with Gabapentin but I can tell you - don't put it sprinkled into food or in anything the dog may bite into and detect & rupture the capsule because it tastes foul to them and they will spit it out - and if like our dog will also start wiping their tongue on the carpet to try to get rid of the taste.
I don't know anything about withdrawal from Gabapentin however as our dog only had it the last years of his life and did not have to stop taking them.