Tapentadol
"Unexpectedly found this page, and read other responses to see others experience with Nucynta. I have been on various doses ranging from 600mg per day (all 100's) to currently taking two 100 extended release tablets per day. My experience has lasted six years now. 
From the very start I loved it because it was effective for my neuropathy. The big bonus was that after a while, say month or two, I was completely confident in my ability to concentrate and do my very detailed work. Now that said, while on the max dose of 600mg I would definitely feel the effects every time I dropped a 100mg. This was the beginning. 
As the dose went down, the ability to concentrate got better and better. my biggest problem was finding a drug store that kept in stock."