It's not the way I would do it, especially since they're different classes of medication, cymbalta being an snri and Paxil an ssri. Further, if you take both at the same time, you won't know if something you feel is a side effect of Cymbalta or of withdrawal from Paxil. Both are very difficult for many to quit. If it were me, I'd want to quit the Paxil slowly, tapering down, getting through any withdrawal before starting another strong med like cymbalta.