Depending on what KING of back pain you have,
Cymbalta is an excellent choice. It is especially effective
for neurological related pain.
All doctors handle the transition from one med to another differently. I personally feel the most optimal way is to SLOWLY and gradually taper down the Effexor until you are on a fairly low dose, then start adding the Cymbalta (also at a low dose), then simultaneously taper the Cymbalta up, while tapering the Effexor down...